diff options
Diffstat (limited to 'manual')
| -rw-r--r-- | manual/Makefile | 4 | ||||
| -rw-r--r-- | manual/chapters.texi | 3 | ||||
| -rw-r--r-- | manual/charset.texi | 2846 | ||||
| -rw-r--r-- | manual/ctype.texi | 521 | ||||
| -rw-r--r-- | manual/filesys.texi | 4 | ||||
| -rw-r--r-- | manual/intro.texi | 2 | ||||
| -rw-r--r-- | manual/lang.texi | 2 | ||||
| -rw-r--r-- | manual/libc.texinfo | 4 | ||||
| -rw-r--r-- | manual/locale.texi | 6 | ||||
| -rw-r--r-- | manual/memory.texi | 3 | ||||
| -rw-r--r-- | manual/stdio.texi | 8 | ||||
| -rw-r--r-- | manual/string.texi | 2 | ||||
| -rw-r--r-- | manual/texis | 2 | ||||
| -rw-r--r-- | manual/top-menu.texi | 70 |
14 files changed, 3432 insertions, 45 deletions
diff --git a/manual/Makefile b/manual/Makefile index e0dad4792c..8eb4d5b69e 100644 --- a/manual/Makefile +++ b/manual/Makefile @@ -49,7 +49,7 @@ endif mkinstalldirs = $(..)scripts/mkinstalldirs chapters = $(addsuffix .texi, \ - intro errno memory ctype string mbyte locale \ + intro errno memory ctype string charset locale \ message search pattern io stdio llio filesys \ pipe socket terminal math arith time setjmp \ signal startup process job nss users sysinfo conf) @@ -74,7 +74,7 @@ libc.dvi: texinfo.tex # Generate the summary from the Texinfo source files for each chapter. summary.texi: stamp-summary ; stamp-summary: summary.awk $(filter-out summary.texi, $(texis)) - $(AWK) -f $^ | sort -t'^L' -df +0 -1 | tr '\014' '\012' > summary-tmp + $(AWK) -f $^ | sort -t' ' -df +0 -1 | tr '\014' '\012' > summary-tmp $(move-if-change) summary-tmp summary.texi touch $@ diff --git a/manual/chapters.texi b/manual/chapters.texi index a5a8a57903..bf7c4c01e0 100644 --- a/manual/chapters.texi +++ b/manual/chapters.texi @@ -3,7 +3,7 @@ @include memory.texi @include ctype.texi @include string.texi -@include mbyte.texi +@include charset.texi @include locale.texi @include message.texi @include search.texi @@ -27,6 +27,7 @@ @include users.texi @include sysinfo.texi @include conf.texi +@include ../crypt/crypt.texi @include ../linuxthreads/linuxthreads.texi @include lang.texi @include header.texi diff --git a/manual/charset.texi b/manual/charset.texi new file mode 100644 index 0000000000..6179128e3c --- /dev/null +++ b/manual/charset.texi @@ -0,0 +1,2846 @@ +@node Character Set Handling, Locales, String and Array Utilities, Top +@c %MENU% Support for extended character sets +@chapter Character Set Handling + +@ifnottex +@macro cal{text} +\text\ +@end macro +@end ifnottex + +Character sets used in the early days of computers had only six, seven, +or eight bits for each character. In no case more bits than would fit +into one byte which nowadays is almost exclusively @w{8 bits} wide. +This of course leads to several problems once not all characters needed +at one time can be represented by the up to 256 available characters. +This chapter shows the functionality which was added to the C library to +overcome this problem. + +@menu +* Extended Char Intro:: Introduction to Extended Characters. +* Charset Function Overview:: Overview about Character Handling + Functions. +* Restartable multibyte conversion:: Restartable multibyte conversion + Functions. +* Non-reentrant Conversion:: Non-reentrant Conversion Function. +* Generic Charset Conversion:: Generic Charset Conversion. +@end menu + + +@node Extended Char Intro +@section Introduction to Extended Characters + +To overcome the limitations of character sets with a 1:1 relation +between bytes and characters people came up with a variety of solutions. +The remainder of this section gives a few examples to help understanding +the design decision made while developing the functionality of the @w{C +library} to support them. + +@cindex internal representation +A distinction we have to make right away is between internal and +external representation. @dfn{Internal representation} means the +representation used by a program while keeping the text in memory. +External representations are used when text is stored or transmitted +through whatever communication channel. + +Traditionally there was no difference between the two representations. +It was equally comfortable and useful to use the same one-byte +representation internally and externally. This changes with more and +larger character sets. + +One of the problems to overcome with the internal representation is +handling text which were externally encoded using different character +sets. Assume a program which reads two texts and compares them using +some metric. The comparison can be usefully done only if the texts are +internally kept in a common format. + +@cindex wide character +For such a common format (@math{=} character set) eight bits are certainly +not enough anymore. So the smallest entity will have to grow: @dfn{wide +characters} will be used. Here instead of one byte one uses two or four +(three are not good to address in memory and more than four bytes seem +not to be necessary). + +@cindex Unicode +@cindex ISO 10646 +As shown in some other part of this manual +@c !!! Ahem, wide char string functions are not yet covered -- drepper +there exists a completely new family of functions which can handle texts +of this kinds in memory. The most commonly used character set for such +internal wide character representations are Unicode and @w{ISO 10646}. +The former is a subset of the later and used when wide characters are +chosen to by 2 bytes (@math{= 16} bits) wide. The standard names of the +@cindex UCS2 +@cindex UCS4 +encodings used in these cases are UCS2 (@math{= 16} bits) and UCS4 +(@math{= 32} bits). + +To represent wide characters the @code{char} type is certainly not +suitable. For this reason the @w{ISO C} standard introduces a new type +which is designed to keep one character of a wide character string. To +maintain the similarity there is also a type corresponding to @code{int} +for those functions which take a single wide character. + +@comment stddef.h +@comment ISO +@deftp {Data type} wchar_t +This data type is used as the base type for wide character strings. +I.e., arrays of objects of this type are the equivalent of @code{char[]} +for multibyte character strings. The type is defined in @file{stddef.h}. + +The @w{ISO C89} standard, where this type was introduced, does not say +anything specific about the representation. It only requires that this +type is capable to store all elements of the basic character set. +Therefore it would be legitimate to define @code{wchar_t} and +@code{char}. This might make sense for embedded systems. + +But for GNU systems this type is always 32 bits wide. It is therefore +capable to represent all UCS4 value therefore covering all of @w{ISO +10646}. Some Unix systems define @code{wchar_t} as a 16 bit type and +thereby follow Unicode very strictly. This is perfectly fine with the +standard but it also means that to represent all characters fro Unicode +and @w{ISO 10646} one has to use surrogate character which is in fact a +multi-wide-character encoding. But this contradicts the purpose of the +@code{wchar_t} type. +@end deftp + +@comment wchar.h +@comment ISO +@deftp {Data type} wint_t +@code{wint_t} is a data type used for parameters and variables which +contain a single wide character. As the name already suggests it is the +equivalent to @code{int} when using the normal @code{char} strings. The +types @code{wchar_t} and @code{wint_t} have often the same +representation if their size if 32 bits wide but if @code{wchar_t} is +defined as @code{char} the type @code{wint_t} must be defined as +@code{int} due to the parameter promotion. + +@pindex wchar.h +This type is defined in @file{wchar.h} and got introduced in the second +amendment to @w{ISO C 89}. +@end deftp + +As there are for the @code{char} data type there also exist macros +specifying the minimum and maximum value representable in an object of +type @code{wchar_t}. + +@comment wchar.h +@comment ISO +@deftypevr Macro wint_t WCHAR_MIN +The macro @code{WCHAR_MIN} evaluates to the minimum value representable +by an object of type @code{wint_t}. + +This macro got introduced in the second amendment to @w{ISO C89}. +@end deftypevr + +@comment wchar.h +@comment ISO +@deftypevr Macro wint_t WCHAR_MAX +The macro @code{WCHAR_MIN} evaluates to the maximum value representable +by an object of type @code{wint_t}. + +This macro got introduced in the second amendment to @w{ISO C89}. +@end deftypevr + +Another special wide character value is the equivalent to @code{EOF}. + +@comment wchar.h +@comment ISO +@deftypevr Macro wint_t WEOF +The macro @code{WEOF} evaluates to a constant expression of type +@code{wint_t} whose value is different from any member of the extended +character set. + +@code{WEOF} need not be the same value as @code{EOF} and unlike +@code{EOF} it also need @emph{not} be negative. I.e., sloppy code like + +@smallexample +@{ + int c; + ... + while ((c = getc (fp)) < 0) + ... +@} +@end smallexample + +@noindent +has to be rewritten to explicitly use @code{WEOF} when wide characters +are used. + +@smallexample +@{ + wint_t c; + ... + while ((c = wgetc (fp)) != WEOF) + ... +@} +@end smallexample + +@pindex wchar.h +This macro was introduced in the second amendment to @w{ISO C89} and is +defined in @file{wchar.h}. +@end deftypevr + + +These internal representations present problems when it comes to storing +and transmitting them. Since a single wide character consists of more +than one byte they are effected by byte-ordering. I.e., machines with +different endianesses would see different value accessing the same data. +This also applies for communication protocols which are all byte-based +and therefore the sender has to decide about splitting the wide +character in bytes. A last but not least important point is that wide +characters often require more storage space than an customized byte +oriented character set. + +@cindex multibyte character +This is why most of the time an external encoding which is different +from the internal encoding is used if the later is UCS2 or UCS4. The +external encoding is byte-based and can be chosen appropriately for the +environment and for the texts to be handled. There exists a variety of +different character sets which can be used which is too much to be +handled completely here. We restrict ourself here to a description of +the major groups. All of the ASCII-based character sets fulfill one +requirement: they are ``filesystem safe''. This means that the +character @code{'/'} is used in the encoding @emph{only} to represent +itself. Things are a bit different for character like EBCDIC but if the +operation system does not understand EBCDIC directly the parameters to +system calls have to be converted first anyhow. + +@itemize @bullet +@item +The simplest character sets are one-byte character sets. There can be +only up to 256 characters (for @w{8 bit} character sets) which is not +sufficient to cover all languages but might be sufficient to handle a +specific text. Another reason to choose this is because of constraints +from interaction with other programs. + +@cindex ISO 2022 +@item +The @w{ISO 2022} standard defines a mechanism for extended character +sets where one character @emph{can} be represented by more than one +byte. This is achieved by associating a state with the text. Embedded +in the text can be characters which can be used to change the state. +Each byte in the text might have a different interpretation in each +state. The state might even influence whether a given byte stands for a +character on its own or whether it has to be combined with some more +bytes. + +@cindex EUC +@cindex SJIS +In most uses of @w{ISO 2022} the defined character sets do not allow +state changes which cover more than the next character. This has the +big advantage that whenever one can identify the beginning of the byte +sequence of a character one can interpret a text correctly. Examples of +character sets using this policy are the various EUC character sets +(used by Sun's operations systems, EUC-JP, EUC-KR, EUC-TW, and EUC-CN) +or SJIS (Shift JIS, a Japanese encoding). + +But there are also character sets using a state which is valid for more +than one character and has to be changed by another byte sequence. +Examples for this are ISO-2022-JP, ISO-2022-KR, and ISO-2022-CN. + +@item +@cindex ISO 6937 +Early attempts to fix 8 bit character sets for other languages using the +Roman alphabet lead to character sets like @w{ISO 6937}. Here bytes +representing characters like the acute accent do not produce output on +there on. One has to combine them with other characters. E.g., the +byte sequence @code{0xc2 0x61} (non-spacing acute accent, following by +lower-case `a') to get the ``small a with acute'' character. To get the +acute accent character on its on one has to write @code{0xc2 0x20} (the +non-spacing acute followed by a space). + +This type of characters sets is quite frequently used in embedded +systems such as video text. + +@item +@cindex UTF-8 +Instead of converting the Unicode or @w{ISO 10646} text used internally +it is often also sufficient to simply use an encoding different then +UCS2/UCS4. The Unicode and @w{ISO 10646} standards even specify such an +encoding: UTF-8. This encoding is able to represent all of @w{ISO +10464} 31 bits in a byte string of length one to seven. + +@cindex UTF-7 +There were a few other attempts to encode @w{ISO 10646} such as UTF-7 +but UTF-8 is today the only encoding which should be used. In fact, +UTF-8 will hopefully soon be the only external which has to be +supported. It proofs to be universally usable and the only disadvantage +is that it favor Latin languages very much by making the byte string +representation of other scripts (Cyrillic, Greek, Asian scripts) longer +than necessary if using a specific character set for these scripts. But +with methods like the Unicode compression scheme one can overcome these +problems and the ever growing memory and storage capacities do the rest. +@end itemize + +The question remaining now is: how to select the character set or +encoding to use. The answer is mostly: you cannot decide about it +yourself, it is decided by the developers of the system or the majority +of the users. Since the goal is interoperability one has to use +whatever the other people one works with use. If there are no +constraints the selection is based on the requirements the expected +circle of users will have. I.e., if a project is expected to only be +used in, say, Russia it is fine to use KOI8-R or a similar character +set. But if at the same time people from, say, Greek are participating +one should use a character set which allows all people to collaborate. + +A general advice here could be: go with the most general character set, +namely @w{ISO 10646}. Use UTF-8 as the external encoding and problems +about users not being able to use their own language adequately are a +thing of the past. + +One final comment about the choice of the wide character representation +is necessary at this point. We have said above that the natural choice +is using Unicode or @w{ISO 10646}. This is not specified in any +standard, though. The @w{ISO C} standard does not specify anything +specific about the @code{wchar_t} type. There might be systems where +the developers decided differently. Therefore one should as much as +possible avoid making assumption about the wide character representation +although GNU systems will always work as described above. If the +programmer uses only the functions provided by the C library to handle +wide character strings there should not be any compatibility problems +with other systems. + +@node Charset Function Overview +@section Overview about Character Handling Functions + +A Unix @w{C library} contains three different sets of functions in two +families to handling character set conversion. The one function family +is specified in the @w{ISO C} standard and therefore is portable even +beyond the Unix world. + +The most commonly known set of functions, coming from the @w{ISO C89} +standard, is unfortunately the least useful one. In fact, these +functions should be avoided whenever possible, especially when +developing libraries (as opposed to applications). + +The second family o functions got introduced in the early Unix standards +(XPG2) and is still part of the latest and greatest Unix standard: +@w{Unix 98}. It is also the most powerful and useful set of functions. +But we will start with the functions defined in the second amendment to +@w{ISO C89}. + +@node Restartable multibyte conversion +@section Restartable Multibyte Conversion Functions + +The @w{ISO C} standard defines functions to convert strings from a +multibyte representation to wide character strings. There are a number +of peculiarities: + +@itemize @bullet +@item +The character set assumed for the multibyte encoding is not specified +as an argument to the functions. Instead the character set specified by +the @code{LC_CTYPE} category of the current locale is used; see +@ref{Locale Categories}. + +@item +The functions handling more than one character at a time require NUL +terminated strings as the argument. I.e., converting blocks of text +does not work unless one can add a NUL byte at an appropriate place. +The GNU C library contains some extensions the standard which allow +specifying a size but basically they also expect terminated strings. +@end itemize + +Despite these limitations the @w{ISO C} functions can very well be used +in many contexts. In graphical user interfaces, for instance, it is not +uncommon to have functions which require text to be displayed in a wide +character string if it is not simple ASCII. The text itself might come +from a file with translations and of course to user should decide about +the current locale which determines the translation and therefore also +the external encoding used. In such a situation (and many others) the +functions described here are perfect. If more freedom while performing +the conversion is necessary take a look at the @code{iconv} functions +(@pxref{Generic Charset Conversion}) + +@menu +* Selecting the Conversion:: Selecting the conversion and its properties. +* Keeping the state:: Representing the state of the conversion. +* Converting a Character:: Converting Single Characters. +* Converting Strings:: Converting Multibyte and Wide Character + Strings. +* Multibyte Conversion Example:: A Complete Multibyte Conversion Example. +@end menu + +@node Selecting the Conversion +@subsection Selecting the conversion and its properties + +We already said above that the currently selected locale for the +@code{LC_CTYPE} category decides about the conversion which is performed +by the functions we are about to describe. Each locale uses its own +character set (given as an argument to @code{localedef}) and this is the +one assumed as the external multibyte encoding. The wide character +character set always is UCS4. So we can see here already where the +limitations of these conversion functions are. + +A characteristic of each multibyte character set is the maximum number +of bytes which can be necessary to represent one character. This +information is quite important when writing code which uses the +conversion functions. In the examples below we will see some examples. +The @w{ISO C} standard defines two macros which provide this information. + + +@comment limits.h +@comment ISO +@deftypevr Macro int MB_LEN_MAX +This macro specifies the maximum number of bytes in the multibyte +sequence for a single character in any of the supported locales. It is +a compile-time constant and it is defined in @file{limits.h}. +@pindex limits.h +@end deftypevr + +@comment stdlib.h +@comment ISO +@deftypevr Macro int MB_CUR_MAX +@code{MB_CUR_MAX} expands into a positive integer expression that is the +maximum number of bytes in a multibyte character in the current locale. +The value is never greater than @code{MB_LEN_MAX}. Unlike +@code{MB_LEN_MAX} this macro need not be a compile-time constant and in +fact, in the GNU C library it is not. + +@pindex stdlib.h +@code{MB_CUR_MAX} is defined in @file{stdlib.h}. +@end deftypevr + +Two different macros are necessary since strictly @w{ISO C89} compiles +do not allow variable length array definitions but still it is desirable +to avoid dynamic allocation. This incomplete piece of code shows the +problem: + +@smallexample +@{ + char buf[MB_LEN_MAX]; + ssize_t len = 0; + + while (! feof (fp)) + @{ + fread (&buf[len], 1, MB_CUR_MAX - len, fp); + /* @r{... process} buf */ + len -= used; + @} +@} +@end smallexample + +The code in the inner loop is expected to have always enough bytes in +the array @var{buf} to convert one multibyte character. The array +@var{buf} has to be sized statically since many compilers do not allow a +variable size. The @code{fread} call makes sure that always +@code{MB_CUR_MAX} bytes are available in @var{buf}. Note that it is no +problem if @code{MB_CUR_MAX} is not a compile-time constant. + + +@node Keeping the state +@subsection Representing the state of the conversion + +@cindex stateful +In the introduction of this chapter it was said that certain character +sets use a @dfn{stateful} encoding. I.e., the encoded values depend in +some way on the previous byte in the text. + +Since the conversion functions allow converting a text in more than one +step we must have a way to pass this information from one call of the +functions to another. + +@comment wchar.h +@comment ISO +@deftp {Data type} mbstate_t +@cindex shift state +A variable of type @code{mbstate_t} can contain all the information +about the @dfn{shift state} needed from one call to a conversion +function to another. + +@pindex wchar.h +This type is defined in @file{wchar.h}. It got introduced in the second +amendment to @w{ISO C89}. +@end deftp + +To use objects of this type the programmer has to define such objects +(normally as local variables on the stack) and pass a pointer to the +object to the conversion functions. This way the conversion function +can update the object if the current multibyte character set is +stateful. + +There is no specific function or initializer to put the state object in +any specific state. The rules are that the object should always +represent the initial state before the first use and this is achieved by +clearing the whole variable with code such as follows: + +@smallexample +@{ + mbstate_t state; + memset (&state, '\0', sizeof (state)); + /* @r{from now on @var{state} can be used.} */ + ... +@} +@end smallexample + +When using the conversion functions to generate output it is often +necessary to test whether current state corresponds to the initial +state. This is necessary, for example, to decide whether or not to emit +escape sequences to set the state to the initial state at certain +sequence points. Communication protocols often require this. + +@comment wchar.h +@comment ISO +@deftypefun int mbsinit (const mbstate_t *@var{ps}) +This function determines whether the state object pointed to by @var{ps} +is in the initial state or not. If @var{ps} is no null pointer or the +object is in the initial state the return value is nonzero. Otherwise +it is zero. + +@pindex wchar.h +This function was introduced in the second amendment to @w{ISO C89} and +is declared in @file{wchar.h}. +@end deftypefun + +Code using this function often looks similar to this: + +@smallexample +@{ + mbstate_t state; + memset (&state, '\0', sizeof (state)); + /* @r{Use @var{state}.} */ + ... + if (! mbsinit (&state)) + @{ + /* @r{Emit code to return to initial state.} */ + fputs ("@r{whatever needed}", fp); + @} + ... +@} +@end smallexample + +@node Converting a Character +@subsection Converting Single Characters + +The most fundamental of the conversion functions are those dealing with +single characters. Please note that this does not always mean single +bytes. But since there is very often a subset of the multibyte +character set which consists of single byte sequences there are +functions to help with converting bytes. One very important and often +applicable scenario is where ASCII is a subpart of the multibyte +character set. I.e., all ASCII characters stand for itself and all +other characters have at least a first byte which is beyond the range +@math{0} to @math{127}. + +@comment wchar.h +@comment ISO +@deftypefun wint_t btowc (int @var{c}) +The @code{btowc} function (``byte to wide character'') converts a valid +single byte character in the initial shift state into the wide character +equivalent using the conversion rules from the currently selected locale +of the @code{LC_CTYPE} category. + +If @code{(unsigned char) @var{c}} is no valid single byte multibyte +character or if @var{c} is @code{EOF} the function returns @code{WEOF}. + +Please note the restriction of @var{c} being tested for validity only in +the initial shift state. There is no @code{mbstate_t} object used from +which the state information is taken and the function also does not use +any static state. + +@pindex wchar.h +This function was introduced in the second amendment of @w{ISO C89} and +is declared in @file{wchar.h}. +@end deftypefun + +Despite the limitation that the single byte value always is interpreted +in the initial state this function is actually useful most of the time. +Most character are either entirely single-byte character sets or they +are extension to ASCII. But then it is possible to write code like this +(not that this specific example is useful): + +@smallexample +wchar_t * +itow (unsigned long int val) +@{ + static wchar_t buf[30]; + wchar_t *wcp = &buf[29]; + *wcp = L'\0'; + while (val != 0) + @{ + *--wcp = btowc ('0' + val % 10); + val /= 10; + @} + if (wcp == &buf[29]) + *--wcp = btowc ('0'); + return wcp; +@} +@end smallexample + +The question is why is it necessary to use such a complicated +implementation and not simply cast L'0' to a wide character. The answer +is that there is no guarantee that the compiler knows about the wide +character set used at runtime. Even if the wide character equivalent of +a given single-byte character is simply the equivalent to casting a +single-byte character to @code{wchar_t} this is no guarantee that this +is the case everywhere. + +There also is a function for the conversion in the other direction. + +@comment wchar.h +@comment ISO +@deftypefun int wctob (wint_t @var{c}) +The @code{wctob} function (``wide character to byte'') takes as the +paremeter a valid wide character. If the multibyte representation for +this character in the initial state is exactly one byte long the return +value of this function is this character. Otherwise the return value is +@code{EOF}. + +@pindex wchar.h +This function was introduced in the second amendment of @w{ISO C89} and +is declared in @file{wchar.h}. +@end deftypefun + +There are more general functions to convert single character from +multibyte representation to wide characters and vice versa. These +functions pose no limit on the length of the multibyte representation +and they also do not require it to be in the initial state. + +@comment wchar.h +@comment ISO +@deftypefun size_t mbrtowc (wchar_t *restrict @var{pwc}, const char *restrict @var{s}, size_t @var{n}, mbstate_t *restrict @var{ps}) +@cindex stateful +The @code{mbrtowc} function (``multibyte restartable to wide +character'') converts the next multibyte character in the string pointed +to by @var{s} into a wide character and stores it in the wide character +string pointed to by @var{pwc}. The conversion is performed according +to the locale currently selected for the @code{LC_CTYPE} category. If +the character set for the locale is stateful the multibyte string is +interpreted in the state represented by the object pointed to by +@var{ps}. If @var{ps} is a null pointer an static, internal state +variable used only by the @code{mbrtowc} variable is used. + +If the next multibyte character corresponds to the NUL wide character +the return value of the function is @math{0} and the state object is +afterwards in the initial state. If the next @var{n} or fewer bytes +form a correct multibyte character the return value is the number of +bytes starting from @var{s} which form the multibyte character. The +conversion state is updated according to the bytes consumed in the +conversion. In both cases the wide character (either the @code{L'\0'} +or the one found in the conversion) is stored in the string pointer to +by @var{pwc} iff @var{pwc} is not null. + +If the first @var{n} bytes of the multibyte string possibly form a valid +multibyte character but there are more than @var{n} bytes needed to +complete it the return value of the function is @code{(size_t) -2} and +no value is stored. Please note that this can happen even if @var{n} +has a value greater or equal to @code{MB_CUR_MAX} since the input might +contain redundant shift sequences. + +If the first @code{n} bytes of the multibyte string cannot possibly +form a valid multibyte character also no value is stored, the global +variable i set to the value @code{EILSEQ} and the function return +@code{(size_t) -1}. The conversion state is afterwards undefined. + +@pindex wchar.h +This function was introduced in the second amendment to @w{ISO C89} and +is declared in @file{wchar.h}. +@end deftypefun + +Using this function is straight forward. A function which copies a +multibyte string into a wide character string while at the same time +converting all lowercase character into uppercase could look like this +(this is not the final version, just an example; it has no error +checking and leaks sometimes memory): + +@smallexample +wchar_t * +mbstouwcs (const char *s) +@{ + size_t len = strlen (s); + wchar_t *result = malloc ((len + 1) * sizeof (wchar_t)); + wchar_t *wcp = result; + wchar_t tmp[1]; + mbstate_t state; + memset (&state, '\0', sizeof (state)); + size_t nbytes; + while ((nbytes = mbrtowc (tmp, s, len, &state)) > 0) + @{ + if (nbytes >= (size_t) -2) + /* Invalid input string. */ + return NULL; + *result++ = towupper (tmp[0]); + len -= nbytes; + s += nbytes; + @} + return result; +@} +@end smallexample + +The use of @code{mbrtowc} should be clear. A single wide character is +stored in @code{@var{tmp}[0]} and the number of consumed bytes is stored +in the variable @var{nbytes}. In case the the conversion was successful +the uppercase variant of the wide character is stored in the +@var{result} array and the pointer to the input string and the number of +available bytes is adjusted. + +The only non-obvious thing about the function might be the way memory is +allocated for the result. The above code uses the fact that there can +never be more wide characters in the converted results than there are +bytes in the multibyte input string. This method yields to a +pessimistic guess about the size of the result and if many wide +character strings have to be constructed this way or the strings are +long, the extra memory required to store the wide character strings +might be significant. It would of course be possible to resize the +allocated memory block to the correct size before returning it. A +better solution might be to allocate just the right amount of space for +the result right away. Unfortunately there is no function to compute +the length of the wide character string directly from the multibyte +string. But there is a function which does part of the work. + +@comment wchar.h +@comment ISO +@deftypefun size_t mbrlen (const char *restrict @var{s}, size_t @var{n}, mbstate_t *@var{ps}) +The @code{mbrlen} function (``multibyte restartable length'') computes +the number of at most @var{n} bytes starting at @var{s} which form the +next valid and complete multibyte character. + +If the next multibyte character corresponds to the NUL wide character +the return value is @math{0}. If the next @var{n} bytes form a valid +multibyte character the number of bytes belonging to this multibyte +character byte sequence is returned. + +If the the first @var{n} bytes possibly form a valid multibyte +character but it is incomplete the return value is @code{(size_t) -2}. +Otherwise the multibyte character sequence is invalid and the return +value is @code{(size_t) -1}. + +The multibyte sequence is interpreted in the state represented by the +object pointer to by @var{ps}. If @var{ps} is a null pointer an state +object local to @code{mbrlen} is used. + +@pindex wchar.h +This function was introduced in the second amendment to @w{ISO C89} and +is declared in @file{wchar.h}. +@end deftypefun + +The tentative reader now will of course note that @code{mbrlen} can be +implemented as + +@smallexample +mbrtowc (NULL, s, n, ps != NULL ? ps : &internal) +@end smallexample + +This is true and in fact is mentioned in the official specification. +Now, how can this function be used to determine the length of the wide +character string created from a multibyte character string? It is not +directly usable but we can define a function @code{mbslen} using it: + +@smallexample +size_t +mbslen (const char *s) +@{ + mbstate_t state; + size_t result = 0; + size_t nbytes; + memset (&state, '\0', sizeof (state)); + while ((nbytes = mbrlen (s, MB_LEN_MAX, &state)) > 0) + @{ + if (nbytes >= (size_t) -2) + /* @r{Something is wrong.} */ + return (size_t) -1; + s += nbytes; + ++result; + @} + return result; +@} +@end smallexample + +This function simply calls @code{mbrlen} for each multibyte character +in the string and counts the number of function calls. Please note that +we here use @code{MB_LEN_MAX} as the size argument in the @code{mbrlen} +call. This is OK since a) this value is larger then the length of the +longest multibyte character sequence and b) because we know that the +string @var{s} ends with a NIL byte which cannot be part of any other +multibyte character sequence but the one representing the NIL wide +character. Therefore the @code{mbrlen} function will never read invalid +memory. + +Now that this function is available (just to make this clear, this +function is @emph{not} part of the GNU C library) we can compute the +number of wide character required to store the converted multibyte +character string @var{s} using + +@smallexample +wcs_bytes = (mbslen (s) + 1) * sizeof (wchar_t); +@end smallexample + +Please note that the @code{mbslen} function is quite inefficient. The +implementation of @code{mbstouwcs} implemented using @code{mbslen} would +have to perform the conversion of the multibyte character input string +twice and this conversion might be quite expensive. So it is necessary +to think about the consequences of using the easier but inprecise method +before doing the work twice. + +@comment wchar.h +@comment ISO +@deftypefun size_t wcrtomb (char *restrict @var{s}, wchar_t @var{wc}, mbstate_t *restrict @var{ps}) +The @code{wcrtomb} function (``wide character restartable to +multibyte'') converts a single wide character into a multibyte string +corresponding to that wide character. + +If @var{s} is a null pointer the resets the the state stored in the +objects pointer to by @var{ps} to the initial state. This can also be +achieved by a call like this: + +@smallexample +wcrtombs (temp_buf, L'\0', ps) +@end smallexample + +@noindent +since when @var{s} is a null pointer @code{wcrtomb} performs as if it +writes into an internal buffer which is guaranteed to be large enough. + +If @var{wc} is the NUL wide character @code{wcrtomb} emits, if +necessary, a shift sequence to get the state @var{ps} into the initial +state followed by a single NUL byte is stored in the string @var{s}. + +Otherwise a byte sequence (possibly including shift sequences) is +written into the string @var{s}. This of course only happens if +@var{wc} is a valid wide character, i.e., it has a multibyte +representation in the character set selected by locale of the +@code{LC_CTYPE} category. If @var{wc} is no valid wide character +nothing is stored in the strings @var{s}, @code{errno} is set to +@code{EILSEQ}, the conversion state in @var{ps} is undefined and the +return value is @code{(size_t) -1}. + +If no error occurred the function returns the number of bytes stored in +the string @var{s}. This includes all byte representing shift +sequences. + +One word about the interface of the function: there is no parameter +specifying the length of the array @var{s}. Instead the function +assumes that there are at least @code{MB_CUR_MAX} bytes available since +this is the maximum length of any byte sequence representing a single +character. So the caller has to make sure that there is enough space +available, otherwise buffer overruns can occur. + +@pindex wchar.h +This function was introduced in the second amendment to @w{ISO C} and is +declared in @file{wchar.h}. +@end deftypefun + +Using this function is as easy as using @code{mbrtowc}. The following +example appends a wide character string to a multibyte character string. +Again, the code is not really useful, it is simply here to demonstrate +the use and some problems. + +@smallexample +char * +mbscatwc (char *s, size_t len, const wchar_t *ws) +@{ + mbstate_t state; + char *wp = strchr (s, '\0'); + len -= wp - s; + memset (&state, '\0', sizeof (state)); + do + @{ + size_t nbytes; + if (len < MB_CUR_LEN) + @{ + /* @r{We cannot guarantee that the next} + @r{character fits into the buffer, so} + @r{return an error.} */ + errno = E2BIG; + return NULL; + @} + nbytes = wcrtomb (wp, *ws, &state); + if (nbytes == (size_t) -1) + /* @r{Error in the conversion.} */ + return NULL; + len -= nbytes; + wp += nbytes; + @} + while (*ws++ != L'\0'); + return s; +@} +@end smallexample + +First the function has to find the end of the string currently in the +array @var{s}. The @code{strchr} call does this very efficiently since a +requirement for multibyte character representations is that the NUL byte +never is used except to represent itself (and in this context, the end +of the string). + +After initializing the state object the loop is entered where the first +task is to make sure there is enough room in the array @var{s}. We +abort if there are not at least @code{MB_CUR_LEN} bytes available. This +is not always optimal but we have no other choice. We might have less +than @code{MB_CUR_LEN} bytes available but the next multibyte character +might also be only one byte long. At the time the @code{wcrtomb} call +returns it is too late to decide whether the buffer was large enough or +not. If this solution is really unsuitable there is a very slow but +more accurate solution. + +@smallexample + ... + if (len < MB_CUR_LEN) + @{ + mbstate_t temp_state; + memcpy (&temp_state, &state, sizeof (state)); + if (wcrtomb (NULL, *ws, &temp_state) > len) + @{ + /* @r{We cannot guarantee that the next} + @r{character fits into the buffer, so} + @r{return an error.} */ + errno = E2BIG; + return NULL; + @} + @} + ... +@end smallexample + +Here we do perform the conversion which might overflow the buffer so +that we are afterwards in the position to make an exact decision about +the buffer size. Please note the @code{NULL} argument for the +destination buffer in the new @code{wcrtomb} call; since we are not +interested in the result at this point this is a nice way to express +this. The most unusual thing about this piece of code certainly is the +duplication of the conversion state object. But think about it: if a +change of the state is necessary to emit the next multibyte character we +want to have the same shift state change performed in the real +conversion. Therefore we have to preserve the initial shift state +information. + +There are certainly many more and even better solutions to this problem. +This example is only meant for educational purposes. + +@node Converting Strings +@subsection Converting Multibyte and Wide Character Strings + +The functions described in the previous section only convert a single +character at a time. Most operations to be performed in real-world +programs include strings and therefore the @w{ISO C} standard also +defines conversions on entire strings. The defined set of functions is +quite limited, though. Therefore contains the GNU C library a few +extensions which are necessary in some important situations. + +@comment wchar.h +@comment ISO +@deftypefun size_t mbsrtowcs (wchar_t *restrict @var{dst}, const char **restrict @var{src}, size_t @var{len}, mbstate_t *restrict @var{ps}) +The @code{mbsrtowcs} function (``multibyte string restartable to wide +character string'') converts an NUL terminated multibyte character +string at @code{*@var{src}} into an equivalent wide character string, +including the NUL wide character at the end. The conversion is started +using the state information from the object pointed to by @var{ps} or +from an internal object of @code{mbsrtowcs} if @var{ps} is a null +pointer. Before returning the state object to match the state after the +last converted character. The state is the initial state if the +terminating NUL byte is reached and converted. + +If @var{dst} is not a null pointer the result is stored in the array +pointed to by @var{dst}, otherwise the conversion result is not +available since it is stored in an internal buffer. + +If @var{len} wide characters are stored in the array @var{dst} before +reaching the end of the input string the conversion stops and @var{len} +is returned. If @var{dst} is a null pointer @var{len} is never checked. + +Another reason for a premature return from the function call is if the +input string contains an invalid multibyte sequence. In this case the +global variable @code{errno} is set to @code{EILSEQ} and the function +returns @code{(size_t) -1}. + +@c XXX The ISO C9x draft seems to have a problem here. It says that PS +@c is not updated if DST is NULL. This is not said straight forward and +@c none of the other functions is described like this. It would make sense +@c to define the function this way but I don't think it is meant like this. + +In all other cases the function returns the number of wide characters +converted during this call. If @var{dst} is not null @code{mbsrtowcs} +stores in the pointer pointed to by @var{src} a null pointer (if the NUL +byte in the input string was reached) or the address of the byte +following the last converted multibyte character. + +@pindex wchar.h +This function was introduced in the second amendment to @w{ISO C} and is +declared in @file{wchar.h}. +@end deftypefun + +The definition of this function has one limitation which has to be +understood. The requirement that @var{dst} has to be a NUL terminated +string provides problems if one wants to convert buffers with text. A +buffer is normally no collection of NUL terminated strings but instead a +continuous collection of lines, separated by newline characters. Now +assume a function to convert one line from a buffer is needed. Since +the line is not NUL terminated the source pointer cannot directly point +into the unmodified text buffer. This means, either one inserts the NUL +byte at the appropriate place for the time of the @code{mbsrtowcs} +function call (which is not doable for a read-only buffer or in a +multi-threaded application) or one copies the line in an extra buffer +where it can be terminated by a NUL byte. Note that it is not in +general possible to limit the number of characters to convert by setting +the parameter @var{len} to any specific value. Since it is not known +how many bytes each multibyte character sequence is in length one always +could do only a guess. + +@cindex stateful +There is still a problem with the method of NUL-terminating a line right +after the newline character which could lead to very strange results. +As said in the description of the @var{mbsrtowcs} function above the +conversion state is guaranteed to be in the initial shift state after +processing the NUL byte at the end of the input string. But this NUL +byte is not really part of the text. I.e., the conversion state after +the newline in the original text could be something different than the +initial shift state and therefore the first character of the next line +is encoded using this state. But the state in question is never +accessible to the user since the conversion stops after the NUL byte. +Fortunately most stateful character sets in use today require that the +shift state after a newline is the initial state but this is no +guarantee. Therefore simply NUL terminating a piece of a running text +is not always the adequate solution. + +The generic conversion +@comment XXX reference to iconv +interface does not have this limitation (it simply works on buffers, not +strings) but there is another way. The GNU C library contains a set of +functions why take additional parameters specifying maximal number of +bytes which are consumed from the input string. This way the problem of +above's example could be solved by determining the line length and +passing this length to the function. + +@comment wchar.h +@comment ISO +@deftypefun size_t wcsrtombs (char *restrict @var{dst}, const wchar_t **restrict @var{src}, size_t @var{len}, mbstate_t *restrict @var{ps}) +The @code{wcsrtombs} function (``wide character string restartable to +multibyte string'') converts the NUL terminated wide character string at +@code{*@var{src}} into an equivalent multibyte character string and +stores the result in the array pointed to by @var{dst}. The NUL wide +character is also converted. The conversion starts in the state +described in the object pointed to by @var{ps} or by a state object +locally to @code{wcsrtombs} in case @var{ps} is a null pointer. If +@var{dst} is a null pointer the conversion is performed as usual but the +result is not available. If all characters of the input string were +successfully converted and if @var{dst} is not a null pointer the +pointer pointed to by @var{src} gets assigned a null pointer. + +If one of the wide characters in the input string has no valid multibyte +character equivalent the conversion stops early, sets the global +variable @code{errno} to @code{EILSEQ}, and returns @code{(size_t) -1}. + +Another reason for a premature stop is if @var{dst} is not a null +pointer and the next converted character would require more than +@var{len} bytes in total to the array @var{dst}. In this case (and if +@var{dest} is not a null pointer) the pointer pointed to by @var{src} is +assigned a value pointing to the wide character right after the last one +successfully converted. + +Except in the case of an encoding error the return value of the function +is the number of bytes in all the multibyte character sequences stored +in @var{dst}. Before returning the state in the object pointed to by +@var{ps} (or the internal object in case @var{ps} is a null pointer) is +updated to reflect the state after the last conversion. The state is +the initial shift state in case the terminating NUL wide character was +converted. + +@pindex wchar.h +This function was introduced in the second amendment to @w{ISO C} and is +declared in @file{wchar.h}. +@end deftypefun + +The restriction mentions above for the @code{mbsrtowcs} function applies +also here. There is no possibility to directly control the number of +input characters. One has to place the NUL wide character at the +correct place or control the consumed input indirectly via the available +output array size (the @var{len} parameter). + +@comment wchar.h +@comment GNU +@deftypefun size_t mbsnrtowcs (wchar_t *restrict @var{dst}, const char **restrict @var{src}, size_t @var{nmc}, size_t @var{len}, mbstate_t *restrict @var{ps}) +The @code{mbsnrtowcs} function is very similar to the @code{mbsrtowcs} +function. All the parameters are the same except for @var{nmc} which is +new. The return value is the same as for @code{mbsrtowcs}. + +This new parameter specifies how many bytes at most can be used from the +multibyte character string. I.e., the multibyte character string +@code{*@var{src}} need not be NUL terminated. But if a NUL byte is +found within the @var{nmc} first bytes of the string the conversion +stops here. + +This function is a GNU extensions. It is meant to work around the +problems mentioned above. Now it is possible to convert buffer with +multibyte character text piece for piece without having to care about +inserting NUL bytes and the effect of NUL bytes on the conversion state. +@end deftypefun + +A function to convert a multibyte string into a wide character string +and display it could be written like this (this is no really useful +example): + +@smallexample +void +showmbs (const char *src, FILE *fp) +@{ + mbstate_t state; + int cnt = 0; + memset (&state, '\0', sizeof (state)); + while (1) + @{ + wchar_t linebuf[100]; + const char *endp = strchr (src, '\n'); + size_t n; + + /* @r{Exit if there is no more line.} */ + if (endp == NULL) + break; + + n = mbsnrtowcs (linebuf, &src, endp - src, 99, &state); + linebuf[n] = L'\0'; + fprintf (fp, "line %d: \"%S\"\n", linebuf); + @} +@} +@end smallexample + +There is no more problem with the state after a call to +@code{mbsnrtowcs}. Since we don't insert characters in the strings +which were not in there right from the beginning and we use @var{state} +only for the conversion of the given buffer there is no problem with +mixing the state up. + +@comment wchar.h +@comment GNU +@deftypefun size_t wcsnrtombs (char *restrict @var{dst}, const wchar_t **restrict @var{src}, size_t @var{nwc}, size_t @var{len}, mbstate_t *restrict @var{ps}) +The @code{wcsnrtombs} function implements the conversion from wide +character strings to multibyte character strings. It is similar to +@code{wcsrtombs} but it takes, just like @code{mbsnrtowcs}, an extra +parameter which specifies the length of the input string. + +No more than @var{nwc} wide characters from the input string +@code{*@var{src}} are converted. If the input string contains a NUL +wide character in the first @var{nwc} character to conversion stops at +this place. + +This function is a GNU extension and just like @code{mbsnrtowcs} is +helps in situations where no NUL terminated input strings are available. +@end deftypefun + + +@node Multibyte Conversion Example +@subsection A Complete Multibyte Conversion Example + +The example programs given in the last sections are only brief and do +not contain all the error checking etc. Therefore here comes a complete +and documented example. It features the @code{mbrtowc} function but it +should be easy to derive versions using the other functions. + +@smallexample +int +file_mbsrtowcs (int input, int output) +@{ + /* @r{Note the use of @code{MB_LEN_MAX}.} + @r{@code{MB_CUR_MAX} cannot portably be used here.} */ + char buffer[BUFSIZ + MB_LEN_MAX]; + mbstate_t state; + int filled = 0; + int eof = 0; + + /* @r{Initialize the state.} */ + memset (&state, '\0', sizeof (state)); + + while (!eof) + @{ + ssize_t nread; + ssize_t nwrite; + char *inp = buffer; + wchar_t outbuf[BUFSIZ]; + wchar_t *outp = outbuf; + + /* @r{Fill up the buffer from the input file.} */ + nread = read (input, buffer + filled, BUFSIZ); + if (nread < 0) + @{ + perror ("read"); + return 0; + @} + /* @r{If we reach end of file, make a note to read no more.} */ + if (nread == 0) + eof = 1; + + /* @r{@code{filled} is now the number of bytes in @code{buffer}.} */ + filled += nread; + + /* @r{Convert those bytes to wide characters--as many as we can.} */ + while (1) + @{ + size_t thislen = mbrtowc (outp, inp, filled, &state); + /* @r{Stop converting at invalid character;} + @r{this can mean we have read just the first part} + @r{of a valid character.} */ + if (thislen == (size_t) -1) + break; + /* @r{We want to handle embedded NUL bytes} + @r{but the return value is 0. Correct this.} */ + if (thislen == 0) + thislen = 1; + /* @r{Advance past this character.} */ + inp += thislen; + filled -= thislen; + ++outp; + @} + + /* @r{Write the wide characters we just made.} */ + nwrite = write (output, outbuf, + (outp - outbuf) * sizeof (wchar_t)); + if (nwrite < 0) + @{ + perror ("write"); + return 0; + @} + + /* @r{See if we have a @emph{real} invalid character.} */ + if ((eof && filled > 0) || filled >= MB_CUR_MAX) + @{ + error (0, 0, "invalid multibyte character"); + return 0; + @} + + /* @r{If any characters must be carried forward,} + @r{put them at the beginning of @code{buffer}.} */ + if (filled > 0) + memmove (inp, buffer, filled); + @} + + return 1; +@} +@end smallexample + + +@node Non-reentrant Conversion +@section Non-reentrant Conversion Function + +The functions described in the last chapter are defined in the second +amendment to @w{ISO C89}. But the original @w{ISO C89} standard also +contained functions for character set conversion. The reason that they +are not described in the first place is that they are almost entirely +useless. + +The problem is that all the functions for conversion defined in @w{ISO +C89} use a local state. This does not only mean that multiple +conversions at the same time (not only when using threads) cannot be +done. It also means that you cannot first convert single characters and +the strings since you cannot say the conversion functions which state to +use. + +These functions are therefore usable only in a very limited set of +situation. One most complete converting the entire string before +starting a new one and each string/text must be converted with the same +function (there is no problem with the library itself; it is guaranteed +that no library function changes the state of any of these functions). +For these reasons it is @emph{highly} requested to use the functions +from the last section. + +@menu +* Non-reentrant Character Conversion:: Non-reentrant Conversion of Single + Characters. +* Non-reentrant String Conversion:: Non-reentrant Conversion of Strings. +* Shift State:: States in Non-reentrant Functions. +@end menu + +@node Non-reentrant Character Conversion +@subsection Non-reentrant Conversion of Single Characters + +@comment stdlib.h +@comment ISO +@deftypefun int mbtowc (wchar_t *@var{result}, const char *@var{string}, size_t @var{size}) +The @code{mbtowc} (``multibyte to wide character'') function when called +with non-null @var{string} converts the first multibyte character +beginning at @var{string} to its corresponding wide character code. It +stores the result in @code{*@var{result}}. + +@code{mbtowc} never examines more than @var{size} bytes. (The idea is +to supply for @var{size} the number of bytes of data you have in hand.) + +@code{mbtowc} with non-null @var{string} distinguishes three +possibilities: the first @var{size} bytes at @var{string} start with +valid multibyte character, they start with an invalid byte sequence or +just part of a character, or @var{string} points to an empty string (a +null character). + +For a valid multibyte character, @code{mbtowc} converts it to a wide +character and stores that in @code{*@var{result}}, and returns the +number of bytes in that character (always at least @code{1}, and never +more than @var{size}). + +For an invalid byte sequence, @code{mbtowc} returns @code{-1}. For an +empty string, it returns @code{0}, also storing @code{0} in +@code{*@var{result}}. + +If the multibyte character code uses shift characters, then +@code{mbtowc} maintains and updates a shift state as it scans. If you +call @code{mbtowc} with a null pointer for @var{string}, that +initializes the shift state to its standard initial value. It also +returns nonzero if the multibyte character code in use actually has a +shift state. @xref{Shift State}. +@end deftypefun + +@comment stdlib.h +@comment ISO +@deftypefun int wctomb (char *@var{string}, wchar_t @var{wchar}) +The @code{wctomb} (``wide character to multibyte'') function converts +the wide character code @var{wchar} to its corresponding multibyte +character sequence, and stores the result in bytes starting at +@var{string}. At most @code{MB_CUR_MAX} characters are stored. + +@code{wctomb} with non-null @var{string} distinguishes three +possibilities for @var{wchar}: a valid wide character code (one that can +be translated to a multibyte character), an invalid code, and @code{0}. + +Given a valid code, @code{wctomb} converts it to a multibyte character, +storing the bytes starting at @var{string}. Then it returns the number +of bytes in that character (always at least @code{1}, and never more +than @code{MB_CUR_MAX}). + +If @var{wchar} is an invalid wide character code, @code{wctomb} returns +@code{-1}. If @var{wchar} is @code{0}, it returns @code{0}, also +storing @code{0} in @code{*@var{string}}. + +If the multibyte character code uses shift characters, then +@code{wctomb} maintains and updates a shift state as it scans. If you +call @code{wctomb} with a null pointer for @var{string}, that +initializes the shift state to its standard initial value. It also +returns nonzero if the multibyte character code in use actually has a +shift state. @xref{Shift State}. + +Calling this function with a @var{wchar} argument of zero when +@var{string} is not null has the side-effect of reinitializing the +stored shift state @emph{as well as} storing the multibyte character +@code{0} and returning @code{0}. +@end deftypefun + +Similar to @code{mbrlen} there is also a non-reentrant function which +computes the length of a multibyte character. It can be defined in +terms of @code{mbtowc}. + +@comment stdlib.h +@comment ISO +@deftypefun int mblen (const char *@var{string}, size_t @var{size}) +The @code{mblen} function with a non-null @var{string} argument returns +the number of bytes that make up the multibyte character beginning at +@var{string}, never examining more than @var{size} bytes. (The idea is +to supply for @var{size} the number of bytes of data you have in hand.) + +The return value of @code{mblen} distinguishes three possibilities: the +first @var{size} bytes at @var{string} start with valid multibyte +character, they start with an invalid byte sequence or just part of a +character, or @var{string} points to an empty string (a null character). + +For a valid multibyte character, @code{mblen} returns the number of +bytes in that character (always at least @code{1}, and never more than +@var{size}). For an invalid byte sequence, @code{mblen} returns +@code{-1}. For an empty string, it returns @code{0}. + +If the multibyte character code uses shift characters, then @code{mblen} +maintains and updates a shift state as it scans. If you call +@code{mblen} with a null pointer for @var{string}, that initializes the +shift state to its standard initial value. It also returns nonzero if +the multibyte character code in use actually has a shift state. +@xref{Shift State}. + +@pindex stdlib.h +The function @code{mblen} is declared in @file{stdlib.h}. +@end deftypefun + + +@node Non-reentrant String Conversion +@subsection Non-reentrant Conversion of Strings + +For convenience reasons the @w{ISO C89} standard defines also functions +to convert entire strings instead of single characters. These functions +suffer from the same problems as their reentrant counterparts from the +second amendment to @w{ISO C89}; see @xref{Converting Strings}. + +@comment stdlib.h +@comment ISO +@deftypefun size_t mbstowcs (wchar_t *@var{wstring}, const char *@var{string}, size_t @var{size}) +The @code{mbstowcs} (``multibyte string to wide character string'') +function converts the null-terminated string of multibyte characters +@var{string} to an array of wide character codes, storing not more than +@var{size} wide characters into the array beginning at @var{wstring}. +The terminating null character counts towards the size, so if @var{size} +is less than the actual number of wide characters resulting from +@var{string}, no terminating null character is stored. + +The conversion of characters from @var{string} begins in the initial +shift state. + +If an invalid multibyte character sequence is found, this function +returns a value of @code{-1}. Otherwise, it returns the number of wide +characters stored in the array @var{wstring}. This number does not +include the terminating null character, which is present if the number +is less than @var{size}. + +Here is an example showing how to convert a string of multibyte +characters, allocating enough space for the result. + +@smallexample +wchar_t * +mbstowcs_alloc (const char *string) +@{ + size_t size = strlen (string) + 1; + wchar_t *buf = xmalloc (size * sizeof (wchar_t)); + + size = mbstowcs (buf, string, size); + if (size == (size_t) -1) + return NULL; + buf = xrealloc (buf, (size + 1) * sizeof (wchar_t)); + return buf; +@} +@end smallexample + +@end deftypefun + +@comment stdlib.h +@comment ISO +@deftypefun size_t wcstombs (char *@var{string}, const wchar_t *@var{wstring}, size_t @var{size}) +The @code{wcstombs} (``wide character string to multibyte string'') +function converts the null-terminated wide character array @var{wstring} +into a string containing multibyte characters, storing not more than +@var{size} bytes starting at @var{string}, followed by a terminating +null character if there is room. The conversion of characters begins in +the initial shift state. + +The terminating null character counts towards the size, so if @var{size} +is less than or equal to the number of bytes needed in @var{wstring}, no +terminating null character is stored. + +If a code that does not correspond to a valid multibyte character is +found, this function returns a value of @code{-1}. Otherwise, the +return value is the number of bytes stored in the array @var{string}. +This number does not include the terminating null character, which is +present if the number is less than @var{size}. +@end deftypefun + +@node Shift State +@subsection States in Non-reentrant Functions + +In some multibyte character codes, the @emph{meaning} of any particular +byte sequence is not fixed; it depends on what other sequences have come +earlier in the same string. Typically there are just a few sequences +that can change the meaning of other sequences; these few are called +@dfn{shift sequences} and we say that they set the @dfn{shift state} for +other sequences that follow. + +To illustrate shift state and shift sequences, suppose we decide that +the sequence @code{0200} (just one byte) enters Japanese mode, in which +pairs of bytes in the range from @code{0240} to @code{0377} are single +characters, while @code{0201} enters Latin-1 mode, in which single bytes +in the range from @code{0240} to @code{0377} are characters, and +interpreted according to the ISO Latin-1 character set. This is a +multibyte code which has two alternative shift states (``Japanese mode'' +and ``Latin-1 mode''), and two shift sequences that specify particular +shift states. + +When the multibyte character code in use has shift states, then +@code{mblen}, @code{mbtowc} and @code{wctomb} must maintain and update +the current shift state as they scan the string. To make this work +properly, you must follow these rules: + +@itemize @bullet +@item +Before starting to scan a string, call the function with a null pointer +for the multibyte character address---for example, @code{mblen (NULL, +0)}. This initializes the shift state to its standard initial value. + +@item +Scan the string one character at a time, in order. Do not ``back up'' +and rescan characters already scanned, and do not intersperse the +processing of different strings. +@end itemize + +Here is an example of using @code{mblen} following these rules: + +@smallexample +void +scan_string (char *s) +@{ + int length = strlen (s); + + /* @r{Initialize shift state.} */ + mblen (NULL, 0); + + while (1) + @{ + int thischar = mblen (s, length); + /* @r{Deal with end of string and invalid characters.} */ + if (thischar == 0) + break; + if (thischar == -1) + @{ + error ("invalid multibyte character"); + break; + @} + /* @r{Advance past this character.} */ + s += thischar; + length -= thischar; + @} +@} +@end smallexample + +The functions @code{mblen}, @code{mbtowc} and @code{wctomb} are not +reentrant when using a multibyte code that uses a shift state. However, +no other library functions call these functions, so you don't have to +worry that the shift state will be changed mysteriously. + + +@node Generic Charset Conversion +@section Generic Charset Conversion + +The conversion functions mentioned so far in this chapter all had in +common that they operate on character sets which are not directly +specified by the functions. The multibyte encoding used is specified by +the currently selected locale for the @code{LC_CTYPE} category. The +wide character set is fixed by the implementation (in the case of GNU C +library it always is @w{ISO 10646}. + +This has of course several problems when it comes to general character +conversion: + +@itemize @bullet +@item +For every conversion where neither the source or destination character +set is the character set of the locale for the @code{LC_CTYPE} category, +one has to change the @code{LC_CTYPE} locale using @code{setlocale}. + +This introduces major problems for the rest of the programs since +several more functions (e.g., the character classification functions, +@xref{Classification of Characters}) use the @code{LC_CTYPE} category. + +@item +Parallel conversions to and from different character sets are not +possible since the @code{LC_CTYPE} selection is global and shared by all +threads. + +@item +If neither the source nor the destination character set is the character +set used for @code{wchar_t} representation there is at least a two-step +process necessary to convert a text using the functions above. One +would have to select the source character set as the multibyte encoding, +convert the text into a @code{wchar_t} text, select the destination +character set as the multibyte encoding and convert the wide character +text to the multibyte (=destination) character set. + +Even if this is possible (which is not guaranteed) it is a very tiring +work. Plus it suffers from the other two raised points even more due to +the steady changing of the locale. +@end itemize + + +The XPG2 standard defines a completely new set of functions which has +none of these limitations. They are not at all coupled to the selected +locales and they but no constraints on the character sets selected for +source and destination. Only the set of available conversions is +limiting them. The standard does not specify that any conversion at all +must be available. It is a measure of the quality of the implementation. + +In the following text first the interface will be described. It is here +shortly named @code{iconv}-interface after the name of the conversion +function. Then the implementation is described as far as interesting to +the advanced user who wants to extend the conversion capabilities. +Comparisons with other implementations will show what trapfalls lie on +the way of portable applications. + +@menu +* Generic Conversion Interface:: Generic Character Set Conversion Interface. +* iconv Examples:: A complete @code{iconv} example. +* Other iconv Implementations:: Some Details about other @code{iconv} + Implementations. +* glibc iconv Implementation:: The @code{iconv} Implementation in the GNU C + library. +@end menu + +@node Generic Conversion Interface +@subsection Generic Character Set Conversion Interface + +This set of functions follows the traditional cycle of using a resource: +open--use--close. The interface consists of three functions, each of +which implement one step. + +Before the interfaces are described it is necessary to introduce a +datatype. Just like other open--use--close interface the functions +introduced here work using a handles and the @file{iconv.h} header +defines a special type for the handles used. + +@comment iconv.h +@comment XPG2 +@deftp {Data Type} iconv_t +This data type is an abstract type defined in @file{iconv.h}. The user +must not assume anything about the definition of this type, it must be +completely opaque. + +Objects of this type can get assigned handles for the conversions using +the @code{iconv} functions. The objects themselves need not be freed but +the conversions for which the handles stand for have to. +@end deftp + +@noindent +The first step is the function to create a handle. + +@comment iconv.h +@comment XPG2 +@deftypefun iconv_t iconv_open (const char *@var{tocode}, const char *@var{fromcode}) +The @code{iconv_open} function has to be used before starting a +conversion. The two parameters this function takes determine the +sources and destination character set for the conversion and if the +implementation has the possibility to perform such a conversion the +function returns a handle. + +If the wanted conversion is not available the function returns +@code{(iconv_t) -1}. In this case the global variable @code{errno} can +have the following values: + +@table @code +@item EMFILE +The process already has @code{OPEN_MAX} file descriptors open. +@item ENFILE +The system limit of open file is reached. +@item ENOMEM +Not enough memory to carry out the operation. +@item EINVAL +The conversion from @var{fromcode} to @var{tocode} is not supported. +@end table + +It is not possible to use the same descriptor in different threads to +perform independent conversions. Within the data structures associated +with the descriptor there is information about the conversion state. +This must of course not be messed up by using it in different +conversions. + +An @code{iconv} descriptor is just a file descriptor as for every use a +new descriptor must be created. The descriptor does not stand for all +of the conversions from @var{fromset} to @var{toset}. + +The GNU C library implementation of @code{iconv_open} has one +significant extension to other implementations. To ease the extension +of the set of available conversions the implementation allows to store +the necessary files with data and code in arbitrary many directories. +How this extensions have to be written will be explained below +(@pxref{glibc iconv Implementation}). Here it is only important to say +that all directories mentioned in the @code{GCONV_PATH} environment +variable are considered if they contain a file @file{gconv-modules}. +These directories need not necessarily be created by the system +administrator. In fact, this extension is introduced to help users +writing and using own, new conversions. Of course this does not work +for security reasons in SUID binaries; in this case only the system +directory is considered and this normally is +@file{@var{prefix}/lib/gconv}. The @code{GCONV_PATH} environment +variable is examined exactly once at the first call of the +@code{iconv_open} function. Later modifications of the variable have no +effect. + +@pindex iconv.h +This function got introduced early in the X/Open Portability Guide, +@w{version 2}. It is supported by all commercial Unices as it is +required for the Unix branding. The quality and completeness of the +implementation varies widely, though. The function is declared in +@file{iconv.h}. +@end deftypefun + +The @code{iconv} implementation can associate large data structure with +the handle returned by @code{iconv_open}. Therefore it is crucial to +free all the resources once all conversions are carried out and the +conversion is not needed anymore. + +@comment iconv.h +@comment XPG2 +@deftypefun int iconv_close (iconv_t @var{cd}) +The @code{iconv_close} function frees all resources associated with the +handle @var{cd} which must have been returned by a successful call to +the @code{iconv_open} function. + +If the function call was successful the return value is @math{0}. +Otherwise it is @math{-1} and @code{errno} is set appropriately. +Defined error are: + +@table @code +@item EBADF +The conversion descriptor is invalid. +@end table + +@pindex iconv.h +This function was introduced together with the rest of the @code{iconv} +functions in XPG2 and it is declared in @file{iconv.h}. +@end deftypefun + +The standard defines only one actual conversion function. This has +therefore the most general interface: it allows conversion from one +buffer to another. Conversion from a file to a buffer, vice versa, or +even file to file can be implemented on top of it. + +@comment iconv.h +@comment XPG2 +@deftypefun size_t iconv (iconv_t @var{cd}, const char **@var{inbuf}, size_t *@var{inbytesleft}, char **@var{outbuf}, size_t *@var{outbytesleft}) +@cindex stateful +The @code{iconv} function converts the text in the input buffer +according to the rules associated with the descriptor @var{cd} and +stores the result in the output buffer. It is possible to call the +function for the same text several times in a row since for stateful +character sets the necessary state information is kept in the data +structures associated with the descriptor. + +The input buffer is specified by @code{*@var{inbuf}} and it contains +@code{*@var{inbytesleft}} bytes. The extra indirection is necessary for +communicating the used input back to the caller (see below). It is +important to note that the buffer pointer is of type @code{char} and the +length is measured in bytes even if the input text is encoded in wide +characters. + +The output buffer is specified in a similar way. @code{*@var{outbuf}} +points to the beginning of the buffer with at least +@code{*@var{outbytesleft}} bytes room for the result. The buffer +pointer again is of type @code{char} and the length is measured in +bytes. If @var{outbuf} or @code{*@var{outbuf}} is a null pointer the +conversion is performed but no output is available. + +If @var{inbuf} is a null pointer the @code{iconv} function performs the +necessary action to put the state of the conversion into the initial +state. This is obviously a no-op for non-stateful encodings, but if the +encoding has a state such a function call might put some byte sequences +in the output buffer which perform the necessary state changes. The +next call with @var{inbuf} not being a null pointer then simply goes on +from the initial state. It is important that the programmer never makes +any assumption on whether the conversion has to deal with states or not. +Even if the input and output character sets are not stateful the +implementation might still have to keep states. This is due to the +implementation chosen for the GNU C library as it is described below. +Therefore an @code{iconv} call to reset the state should always be +performed if some protocol requires this for the output text. + +The conversion stops for three reasons. The first is that all +characters from the input buffer are converted. This actually can mean +two things: really all bytes from the input buffer are consumed or the +there are some bytes at the end of the buffer which possibly can form a +complete character but the input is incomplete. The second reason for a +stop is when the output buffer is full. And the third reason is that +the input contains invalid characters. + +In all these cases the buffer pointers after the last successful +conversion, for input and output buffer, are stored in @var{inbuf} and +@var{outbuf} and the available room in each buffer is stored in +@var{inbytesleft} and @var{outbytesleft}. + +Since the character sets selected in the @code{iconv_open} call can be +almost arbitrary there can be situations where the input buffer contains +valid characters which have no identical representation in the output +character set. The behavior in this situation is undefined. The +@emph{current} behavior of the GNU C library in this situation is to +return with an error immediately. This certainly is not the most +desirable solution. Therefore future versions will provide better ones +but they are not yet finished. + +If all input from the input buffer is successfully converted and stored +in the output buffer the function returns the number of conversion +performed. In all other cases the return value is @code{(size_t) -1} +and @code{errno} is set appropriately. In this case the value pointed +to by @var{inbytesleft} is nonzero. + +@table @code +@item EILSEQ +The conversion stopped because of an invalid byte sequence in the input. +After the call @code{*@var{inbuf}} points at the first byte of the +invalid byte sequence. + +@item E2BIG +The conversion stopped because it ran out of space in the output buffer. + +@item EINVAL +The conversion stopped because of an incomplete byte sequence at the end +of the input buffer. + +@item EBADF +The @var{cd} argument is invalid. +@end table + +@pindex iconv.h +This function was introduced in the XPG2 standard and is declared in the +@file{iconv.h} header. +@end deftypefun + +The definition of the @code{iconv} function is quite good overall. It +provides quite flexible functionality. The only problems lie in the +boundary cases which are incomplete byte sequences at the end of the +input buffer and invalid input. A third problem, which is not really a +design problem, is the way conversions are selected. The standard does +not say anything about the legitimate names, a minimal set of available +conversions. We will see how this has negative impacts in the +discussion of other implementations further down. + + +@node iconv Examples +@subsection A complete @code{iconv} example + +The example below features a solution for a common problem. Given that +one knows the internal encoding used by the system for @code{wchar_t} +strings one often is in the position to read text from a file and store +it in wide character buffers. One can do this using @code{mbsrtowcs} +but then we run into the problems discussed above. + +@smallexample +int +file2wcs (int fd, const char *charset, wchar_t *outbuf, size_t avail) +@{ + char inbuf[BUFSIZ]; + size_t insize = 0; + char *wrptr = (char *) outbuf; + int result = 0; + iconv_t cd; + + cd = iconv_open ("UCS4", charset); + if (cd == (iconv_t) -1) + @{ + /* @r{Something went wrong.} */ + if (errno == EINVAL) + error (0, 0, "conversion from `%s' to `UCS4' no available", + charset); + else + perror ("iconv_open"); + + /* @r{Terminate the output string.} */ + *outbuf = L'\0'; + + return -1; + @} + + while (avail > 0) + @{ + size_t nread; + size_t nconv; + char *inptr = inbuf; + + /* @r{Read more input.} */ + nread = read (fd, inbuf + insize, sizeof (inbuf) - insize); + if (nread == 0) + @{ + /* @r{When we come here the file is completely read.} + @r{This still could mean there are some unused} + @r{characters in the @code{inbuf}. Put them back.} */ + if (lseek (fd, -insize, SEEK_CUR) == -1) + result = -1; + break; + @} + insize += nread; + + /* @r{Do the conversion.} */ + nconv = iconv (cd, &inptr, &insize, &wrptr, &avail); + if (nconv == (size_t) -1) + @{ + /* @r{Not everything went right. It might only be} + @r{an unfinished byte sequence at the end of the} + @r{buffer. Or it is a real problem.} */ + if (errno == EINVAL) + /* @r{This is harmless. Simply move the unused} + @r{bytes to the beginning of the buffer so that} + @r{they can be used in the next round.} */ + memmove (inbuf, inptr, insize); + else + @{ + /* @r{It is a real problem. Maybe we ran out of} + @r{space in the output buffer or we have invalid} + @r{input. In any case back the file pointer to} + @r{the position of the last processed byte.} */ + lseek (fd, -insize, SEEK_CUR); + result = -1; + break; + @} + @} + @} + + /* @r{Terminate the output string.} */ + *((wchar_t *) wrptr) = L'\0'; + + if (iconv_close (cd) != 0) + perror ("iconv_close"); + + return (wchar_t *) wrptr - outbuf; +@} +@end smallexample + +@cindex stateful +This example shows the most important aspects of using the @code{iconv} +functions. It shows how successive calls to @code{iconv} can be used to +convert large amounts of text. The user does not have to care about +stateful encodings as the functions take care of everything. + +An interesting point is the case where @code{iconv} return an error and +@code{errno} is set to @code{EINVAL}. This is not really an error in +the transformation. It can happen whenever the input character set +contains byte sequences of more than one byte for some character and +texts are not processed in one piece. In this case there is a chance +that a multibyte sequence is cut. The caller than can simply read the +remainder of the takes and feed the offending bytes together with new +character from the input to @code{iconv} and continue the work. The +internal state kept in the descriptor is @emph{not} unspecified after +such an event as it is the case with the conversion functions from the +@w{ISO C} standard. + +The example also shows the problem of using wide character strings with +@code{iconv}. As explained in the description of the @code{iconv} +function above the function always takes a pointer to a @code{char} +array and the available space is measured in bytes. In the example the +output buffer is a wide character buffer. Therefore we use a local +variable @var{wrptr} of type @code{char *} which is used in the +@code{iconv} calls. + +This looks rather innocent but can lead to problems on platforms which +have tight restriction on alignment. Therefore the caller of +@code{iconv} has to make sure that the pointers passed are suitable for +access of characters from the appropriate character set. Since in the +above case the input parameter to the function is a @code{wchar_t} +pointer this is the case (unless the user violates alignment when +computing the parameter). But in other situations, especially when +writing generic functions where one does not know what type of character +set on uses and therefore treats text as a sequence of bytes, it might +become tricky. + + +@node Other iconv Implementations +@subsection Some Details about other @code{iconv} Implementations + +This is not really the place to discuss the @code{iconv} implementation +of other systems but it is necessary to know a bit about them to write +portable programs. The above mentioned problems with the specification +of the @code{iconv} functions can lead to portability issues. + +The first thing to notice is that due to the large number of character +sets in use it is certainly not practical to encode the conversions +directly in the C library. Therefore the conversion information must +come from files outside the C library. This is usually in one or both +of the following ways: + +@itemize @bullet +@item +The C library contains a set of generic conversion functions which can +read the needed conversion tables and other information from data files. +These files get loaded when necessary. + +This solution is problematic as it is only with very much effort +applicable to all character set (maybe it is even impossible). The +differences in structure of the different character sets is so large +that many different variants of the table processing functions must be +developed. On top of this the generic nature of these functions make +them slower than specifically implemented functions. + +@item +The C library only contains a framework which can dynamically load +object files and execute the therein contained conversion functions. + +This solution provides much more flexibility. The C library itself +contains only very little code and therefore reduces the general memory +footprint. Also, with a documented interface between the C library and +the loadable modules it is possible for third parties to extend the set +of available conversion modules. A drawback of this solution is that +dynamic loading must be available. +@end itemize + +Some implementations in commercial Unices implement a mixture of these +possibilities, the majority only the second solution. This often leads +to problems, though. Since the modules with the conversion modules must +be dynamically loaded the system must have this possibility for all +programs. But this is not the case. At least some platforms (if no +all) are not able to dynamically load objects if the program is linked +statically. This is often solved by outlawing static linking entirely +but sure it is a weak solution. The GNU C library does not have this +restriction though it also uses dynamic loading. The danger is that one +get acquainted with this and forgets about the restriction on other +systems. + +A second thing to know about other @code{iconv} implementations is that +the number of available conversion is often very limited. Some +implementations provide in the standard release (not the special +international release, if something exists) at most 100 to 200 +conversion possibilities. This does not mean 200 different character +sets are supported. E.g., conversions from one character set to a set +of, say, 10 others counts as 10 conversion. Together with the other +direction this makes already 20. One can imagine the thin coverage +these platform provide. Some Unix vendors even provide only a handful +of conversions which renders them useless for almost all uses. + +This directly leads to a third and probably the most problematic point. +The way the @code{iconv} conversion functions are implemented on all +known Unix system the availability of the conversion functions from +character set @math{@cal{A}} to @math{@cal{B}} and the conversion from +@math{@cal{B}} to @math{@cal{C}} does @emph{not} imply that the +conversion from @math{@cal{A}} to @math{@cal{C}} is available. + +This might not seem unreasonable and problematic at first but it is a +quite big problem as one will notice shortly after hitting it. To show +the problem we assume to write a program which has to convert from +@math{@cal{A}} to @math{@cal{C}}. A call like + +@smallexample +cd = iconv_open ("@math{@cal{C}}", "@math{@cal{A}}"); +@end smallexample + +@noindent +does fail according to the assumption above. But what does the program +do now? The conversion is really necessary and therefore simply giving +up is no possibility. + +First this is of course a nuisance. The @code{iconv} function should +take care of this. But second, how should the program proceed from here +on? If it would try to convert to character set @math{@cal{B}} first +the two @code{iconv_open} calls + +@smallexample +cd1 = iconv_open ("@math{@cal{B}}", "@math{@cal{A}}"); +@end smallexample + +@noindent +and + +@smallexample +cd2 = iconv_open ("@math{@cal{C}}", "@math{@cal{B}}"); +@end smallexample + +@noindent +will succeed but how to find @math{@cal{B}}? + +The answer is unfortunately: there is no general solution. On some +systems guessing might help. On those systems most character sets can +convert to and from UTF8 encoded @w{ISO 10646} or Unicode text. Beside +this only some very system-specific methods can help. Since the +conversion functions come from loadable modules and these modules must +be stored somewhere in the filesystem, one @emph{could} try to find them +and determine from the available file which conversions are available +and whether there is an indirect route from @math{@cal{A}} to +@math{@cal{C}}. + +This shows one of the design errors of @code{iconv} mentioned above. It +should at least be possible to determine the list of available +conversion programmatically so that if @code{iconv_open} says there is +no such conversion, one could make sure this also is true for indirect +routes. + + +@node glibc iconv Implementation +@subsection The @code{iconv} Implementation in the GNU C library + +After reading about the problems of @code{iconv} implementations in the +last section it is certainly good to read here that the implementation +in the GNU C library has none of the problems mentioned above. But step +by step now. We will now address the points raised above. The +evaluation is based on the current state of the development (as of +January 1999). The development of the @code{iconv} functions is not +entirely finished by now but things can only get better. + +The GNU C library's @code{iconv} implementation uses shared loadable +modules to implement the conversions. A very small number of +conversions are built into the library itself but these are only rather +trivial conversions. + +All the benefits of loadable modules are available in the GNU C library +implementation. This is especially interesting since the interface is +well documented (see below) and it therefore is easy to write new +conversion modules. The drawback of using loadable object is not a +problem in the GNU C library, at least on ELF systems. Since the +library is able to load shared objects even in statically linked +binaries this means that static linking must not be forbidden in case +one wants to use @code{iconv}. + +The second mentioned problems is the number of supported conversions. +First, the GNU C library supports more then 150 character. And the was +the implementation is designed the number of supported conversions is +greater than 22350 (@math{150} times @math{149}). If any conversion +from or to a character set is missing it can easily be added. + +This high number is due to the fact that the GNU C library +implementation of @code{iconv} does not have the third problem mentioned +above. I.e., whenever there is a conversion from a character set +@math{@cal{A}} to @math{@cal{B}} and from @math{@cal{B}} to +@math{@cal{C}} it always is possible to convert from @math{@cal{A}} to +@math{@cal{C}} directly. If the @code{iconv_open} returns an error and +sets @code{errno} to @code{EINVAL} this really means there is no known +way, directly or indirectly, to perform the wanted conversion. + +@cindex triangulation +This is achieved by providing for each character set a conversion from +and to UCS4 encoded @w{ISO 10646}. Using @w{ISO 10646} as an +intermediate representation it is possible to ``triangulate''. + +There is no inherent requirement to provide a conversion to @w{ISO +10646} for a new character set and it is also possible to provide other +conversion where neither source not destination character set is @w{ISO +10646}. The currently existing set of conversion is simply meant to +convert all conversions which might be of interest. What could be done +in future is improving the speed of certain conversions. + +@cindex ISO-2022-JP +@cindex EUC-JP +Since all currently available conversions use the triangulation methods +often used conversion run unnecessarily slow. If, e.g., somebody often +needs the conversion from ISO-2022-JP to EUC-JP it is not the best way +to convert the input to @w{ISO 10646} first. The two character sets of +interest are much more similar to each other than to @w{ISO 10646}. + +In such a situation one can easy write a new conversion and provide it +as a better alternative. The GNU C library @code{iconv} implementation +would automatically use the module implementing the conversion if it is +specified to be more efficient. + +@subsubsection Format of @file{gconv-modules} files + +All information about the available conversions comes from a file named +@file{gconv-modules} which can be found in any of the directories along +the @code{GCONV_PATH}. The @file{gconv-modules} files are line-oriented +text files, where each of the lines has one of the following formats: + +@itemize @bullet +@item +If the first non-whitespace character is a @kbd{#} the line contains +only comments is is ignored. + +@item +Lines starting with @code{alias} define an alias name for a character +set. There are two more words expected on the line. The first one +defines the alias name and the second defines the original name of the +character set. The effect is that it is possible to use the alias name +in the @var{fromset} or @var{toset} parameters of @code{iconv_open} and +achieve the same result as when using the real character set name. + +This is quite important as a character set has often many different +names. There is normally always an official name but this need not +correspond to the most popular name. Beside this many character sets +have special names which are somehow constructed. E.g., all character +sets specified by the ISO have an alias of the form +@code{ISO-IR-@var{nnn}} where @var{nnn} is the registration number. +This allows programs which know about the registration number to +construct character set names and use them in @code{iconv_open} calls. +More on the available names and alias follows below. + +@item +Lines starting with @code{module} introduce an available conversion +module. These lines must contain three or four more words. + +The first word specifies the source character set, the second word the +destination character set of conversion implemented in this module. The +third word is the name of the loadable module. The filename is +constructed by appending the usual shared object prefix (normally +@file{.so}) and this file is then supposed to be found in the same +directory the @file{gconv-modules} file is in. The last word on the +line, which is optional, is a numeric value representing the cost of the +conversion. If this word is missing a cost of @math{1} is assumed. The +numeric value itself does not matter that much; what counts are the +relative values of the sums of costs for all possible conversion paths. +Below is a more precise description of the use of the cost value. +@end itemize + +Coming back to the example where one has written a module to directly +convert from ISO-2022-JP to EUC-JP and back. All what has to be done is +to put the new module, be its name ISO2022JP-EUCJP.so, in a directory +and add a file @file{gconv-modules} with the following content in the +same directory: + +@smallexample +module ISO-2022-JP// EUC-JP// ISO2022JP-EUCJP 1 +module EUC-JP// ISO-2022-JP// ISO2022JP-EUCJP 1 +@end smallexample + +To see why this is enough it is necessary to understand how the +conversion used by @code{iconv} and described in the descriptor is +selected. The approach to this problem is quite simple. + +At the first call of the @code{iconv_open} function the program reads +all available @file{gconv-modules} files and builds up two tables: one +containing all the known aliases and another which contains the +information about the conversions and which shared object implements +them. + +@subsubsection Finding the conversion path in @code{iconv} + +The set of available conversions form a directed graph with weighted +edges. The weights on the edges are of course the costs specified in +the @file{gconv-modules} files. The @code{iconv_open} function +therefore uses an algorithm suitable to search for the best path in such +a graph and so constructs a list of conversions which must be performed +in succession to get the transformation from the source to the +destination character set. + +Now it can be easily seen why the above @file{gconv-modules} files +allows the @code{iconv} implementation to pick up the specific +ISO-2022-JP to EUC-JP conversion module instead of the conversion coming +with the library itself. Since the later conversion takes two steps +(from ISO-2022-JP to @w{ISO 10646} and then from @w{ISO 10646} to +EUC-JP) the cost is @math{1+1 = 2}. But the above @file{gconv-modules} +file specifies that the new conversion modules can perform this +conversion with only the cost of @math{1}. + +A bit mysterious about the @file{gconv-modules} file above (and also the +file coming with the GNU C library) are the names of the character sets +specified in the @code{module} lines. Why do almost all the names end +in @code{//}? And this is not all: the names can actually be regular +expressions. At this point of time this mystery should not be revealed. +Sorry! @strong{The part of the implementation where this is used is not +yet finished. For now please simply follow the existing examples. +It'll become clearer once it is. --drepper} + +A last remark about the @file{gconv-modules} is about the names not +ending with @code{//}. There often is a character set named +@code{INTERNAL} mentioned. From the discussion above and the chosen +name it should have become clear that this is the names for the +representation used in the intermediate step of the triangulation. We +have said that this is UCS4 but actually it is not quite right. The +UCS4 specification also includes the specification of the byte ordering +used. Since an UCS4 value consists of four bytes a stored value is +effected by byte ordering. The internal representation is @emph{not} +the same as UCS4 in case the byte ordering of the processor (or at least +the running process) is not the same as the one required for UCS4. This +is done for performance reasons as one does not want to perform +unnecessary byte-swapping operations if one is not interested in actually +seeing the result in UCS4. To avoid trouble with endianess the internal +representation consistently is named @code{INTERNAL} even on big-endian +systems where the representations are identical. + +@subsubsection @code{iconv} module data structures + +So far this section described how modules are located and considered to +be used. What remains to be described is the interface of the modules +so that one can write new ones. This section describes the interface as +it is in use in January 1999. The interface will change in future a bit +but hopefully only in an upward compatible way. + +The definitions necessary to write new modules are publically available +in the non-standard header @file{gconv.h}. The following text will +therefore describe the definitions from this header file. But first it +is necessary to get an overview. + +From the perspective of the user of @code{iconv} the interface is quite +simple: the @code{iconv_open} function returns a handle which can be +used in calls @code{iconv} and finally the handle is freed with a call +to @code{iconv_close}. The problem is: the handle has to be able to +represent the possibly long sequences of conversion steps and also the +state of each conversion since the handle is all which is passed to the +@code{iconv} function. Therefore the data structures are really the +elements to understanding the implementation. + +We need two different kinds of data structures. The first describes the +conversion and the second describes the state etc. There are really two +type definitions like this in @file{gconv.h}. +@pindex gconv.h + +@comment gconv.h +@comment GNU +@deftp {Data type} {struct gconv_step} +This data structure describes one conversion a module can perform. For +each function in a loaded module with conversion functions there is +exactly one object of this type. This object is shared by all users of +the conversion. I.e., this object does not contain any information +corresponding to an actual conversion. It only describes the conversion +itself. + +@table @code +@item struct gconv_loaded_object *shlib_handle +@itemx const char *modname +@itemx int counter +All these elements of the structure are used internally in the C library +to coordinate loading and unloading the shared. One must not expect any +of the other elements be available or initialized. + +@item const char *from_name +@itemx const char *to_name +@code{from_name} and @code{to_name} contain the names of the source and +destination character sets. They can be used to identify the actual +conversion to be carried out since one module might implement +conversions for more than one character set and/or direction. + +@item gconv_fct fct +@itemx gconv_init_fct init_fct +@itemx gconv_end_fct end_fct +These elements contain pointers to the functions in the loadable module. +The interface will be explained below. + +@item int min_needed_from +@itemx int max_needed_from +@itemx int min_needed_to +@itemx int max_needed_to; +These values have to be filled in the the init function of the module. +The @code{min_needed_from} value specifies how many bytes a character of +the source character set at least needs. The @code{max_needed_from} +specifies the maximum value which also includes possible shift +sequences. + +The @code{min_needed_to} and @code{max_needed_to} values serve the same +purpose but this time for the destination character set. + +It is crucial that these values are accurate since otherwise the +conversion functions will have problems or not work at all. + +@item int stateful +This element must also be initialized by the init function. It is +nonzero if the source character set is stateful. Otherwise it is zero. + +@item void *data +This element can be used freely by the conversion functions in the +module. It can be used to communicate extra information from one call +to another. It need not be initialized if not needed at all. If this +element gets assigned a pointer to dynamically allocated memory +(presumably in the init function) it has to be made sure that the end +function deallocates the memory. Otherwise the application will leak +memory. + +It is important to be aware that this data structure is shared by all +users of this specification conversion and therefore the @code{data} +element must not contain data specific to one specific use of the +conversion function. +@end table +@end deftp + +@comment gconv.h +@comment GNU +@deftp {Data type} {struct gconv_step_data} +This is the data structure which contains the information specific to +each use of the conversion functions. + +@table @code +@item char *outbuf +@itemx char *outbufend +These elements specify the output buffer for the conversion step. The +@code{outbuf} element points to the beginning of the buffer and +@code{outbufend} points to the byte following the last byte in the +buffer. The conversion function must not assume anything about the size +of the buffer but it can be safely assumed the there is room for at +least one complete character in the output buffer. + +Once the conversion is finished and the conversion is the last step the +@code{outbuf} element must be modified to point after last last byte +written into the buffer to signal how much output is available. If this +conversion step is not the last one the element must not be modified. +The @code{outbufend} element must not be modified. + +@item int is_last +This element is nonzero if this conversion step is the last one. This +information is necessary for the recursion. See the description of the +conversion function internals below. This element must never be +modified. + +@item int invocation_counter +The conversion function can use this element to see how many calls of +the conversion function already happened. Some character sets require +when generating output a certain prolog and by comparing this value with +zero one can find out whether it is the first call and therefore the +prolog should be emitted or not. This element must never be modified. + +@item int internal_use +This element is another one rarely used but needed in certain +situations. It got assigned a nonzero value in case the conversion +functions are used to implement @code{mbsrtowcs} et.al. I.e., the +function is not used directly through the @code{iconv} interface. + +This sometimes makes a difference as it is expected that the +@code{iconv} functions are used to translate entire texts while the +@code{mbsrtowcs} functions are normally only used to convert single +strings and might be used multiple times to convert entire texts. + +But in this situation we would have problem complying with some rules of +the character set specification. Some character sets require a prolog +which must appear exactly once for an entire text. If a number of +@code{mbsrtowcs} calls are used to convert the text only the first call +must add the prolog. But since there is no communication between the +different calls of @code{mbsrtowcs} the conversion functions have no +possibility to find this out. The situation is different for sequences +of @code{iconv} calls since the handle allows to access the needed +information. + +This element is mostly used together with @code{invocation_counter} in a +way like this: + +@smallexample +if (!data->internal_use && data->invocation_counter == 0) + /* @r{Emit prolog.} */ + ... +@end smallexample + +This element must never be modified. + +@item mbstate_t *statep +The @code{statep} element points to an object of type @code{mbstate_t} +(@pxref{Keeping the state}). The conversion of an stateful charater +set must use the object pointed to by this element to store information +about the conversion state. The @code{statep} element itself must never +be modified. + +@item mbstate_t __state +This element @emph{never} must be used directly. It is only part of +this structure to have the needed space allocated. +@end table +@end deftp + +@subsubsection @code{iconv} module interfaces + +With the knowledge about the data structures we now can describe the +conversion functions itself. To understand the interface a bit of +knowledge about the functionality in the C library which loads the +objects with the conversions is necessary. + +It is often the case that one conversion is used more than once. I.e., +there are several @code{iconv_open} calls for the same set of character +sets during one program run. The @code{mbsrtowcs} et.al.@: functions in +the GNU C library also use the @code{iconv} functionality which +increases the number of uses of the same functions even more. + +For this reason the modules do not get loaded exclusively for one +conversion. Instead a module once loaded can be used by arbitrary many +@code{iconv} or @code{mbsrtowcs} calls at the same time. The splitting +of the information between conversion function specific information and +conversion data makes this possible. The last section showed the two +data structure used to do this. + +This is of course also reflected in the interface and semantic of the +functions the modules must provide. There are three functions which +must have the following names: + +@table @code +@item gconv_init +The @code{gconv_init} function initializes the conversion function +specific data structure. This very same object is shared by all +conversion which use this conversion and therefore no state information +about the conversion itself must be stored in here. If a module +implements more than one conversion the @code{gconv_init} function will be +called multiple times. + +@item gconv_end +The @code{gconv_end} function is responsible to free all resources +allocated by the @code{gconv_init} function. If there is nothing to do +this function can be missing. Special care must be taken if the module +implements more than one conversion and the @code{gconv_init} function +does not allocate the same resources for all conversions. + +@item gconv +This is the actual conversion function. It is called to convert one +block of text. It gets passed the conversion step information +initialized by @code{gconv_init} and the conversion data, specific to +this use of the conversion functions. +@end table + +There are three data types defined for the three module interface +function and these define the interface. + +@comment gconv.h +@comment GNU +@deftypevr {Data type} int (*gconv_init_fct) (struct gconv_step *) +This specifies the interface of the initialization function of the +module. It is called exactly once for each conversion the module +implements. + +As explained int the description of the @code{struct gconv_step} data +structure above the initialization function has to initialize parts of +it. + +@table @code +@item min_needed_from +@itemx max_needed_from +@itemx min_needed_to +@itemx max_needed_to +These elements must be initialized to the exact numbers of the minimum +and maximum number of bytes used by one character in the source and +destination character set respectively. If the characters all have the +same size the minimum and maximum values are the same. + +@item stateful +This element must be initialized to an nonzero value if the source +character set is stateful. Otherwise it must be zero. +@end table + +If the initialization function needs to communication some information +to the conversion function this can happen using the @code{data} element +of the @code{gconv_step} structure. But since this data is shared by +all the conversion is must not be modified by the conversion function. +How this can be used is shown in the example below. + +@smallexample +#define MIN_NEEDED_FROM 1 +#define MAX_NEEDED_FROM 4 +#define MIN_NEEDED_TO 4 +#define MAX_NEEDED_TO 4 + +int +gconv_init (struct gconv_step *step) +@{ + /* @r{Determine which direction.} */ + struct iso2022jp_data *new_data; + enum direction dir = illegal_dir; + enum variant var = illegal_var; + int result; + + if (__strcasecmp (step->from_name, "ISO-2022-JP//") == 0) + @{ + dir = from_iso2022jp; + var = iso2022jp; + @} + else if (__strcasecmp (step->to_name, "ISO-2022-JP//") == 0) + @{ + dir = to_iso2022jp; + var = iso2022jp; + @} + else if (__strcasecmp (step->from_name, "ISO-2022-JP-2//") == 0) + @{ + dir = from_iso2022jp; + var = iso2022jp2; + @} + else if (__strcasecmp (step->to_name, "ISO-2022-JP-2//") == 0) + @{ + dir = to_iso2022jp; + var = iso2022jp2; + @} + + result = GCONV_NOCONV; + if (dir != illegal_dir) + @{ + new_data = (struct iso2022jp_data *) + malloc (sizeof (struct iso2022jp_data)); + + result = GCONV_NOMEM; + if (new_data != NULL) + @{ + new_data->dir = dir; + new_data->var = var; + step->data = new_data; + + if (dir == from_iso2022jp) + @{ + step->min_needed_from = MIN_NEEDED_FROM; + step->max_needed_from = MAX_NEEDED_FROM; + step->min_needed_to = MIN_NEEDED_TO; + step->max_needed_to = MAX_NEEDED_TO; + @} + else + @{ + step->min_needed_from = MIN_NEEDED_TO; + step->max_needed_from = MAX_NEEDED_TO; + step->min_needed_to = MIN_NEEDED_FROM; + step->max_needed_to = MAX_NEEDED_FROM + 2; + @} + + /* @r{Yes, this is a stateful encoding.} */ + step->stateful = 1; + + result = GCONV_OK; + @} + @} + + return result; +@} +@end smallexample + +The function first checks which conversion is wanted. The module from +which this function is taken implements four different conversion and +which one is selected can be determined by comparing the names. The +comparison should always be done without paying attention to the case. + +Then a data structure is allocated which contains the necessary +information about which conversion is selected. The data structure +@code{struct iso2022jp_data} is locally defined since outside the module +this data is not used at all. Please note that if all four conversions +this modules supports are requested there are four data blocks. + +One interesting thing is the initialization of the @code{min_} and +@code{max_} elements of the step data object. A single ISO-2022-JP +character can consist of one to four bytes. Therefore the +@code{MIN_NEEDED_FROM} and @code{MAX_NEEDED_FROM} macros are defined +this way. The output is always the @code{INTERNAL} character set (aka +UCS4) and therefore each character consists of exactly four bytes. For +the conversion from @code{INTERNAL} to ISO-2022-JP we have to take into +account that escape sequences might be necessary to switch the character +sets. Therefore the @code{max_needed_to} element for this direction +gets assigned @code{MAX_NEEDED_FROM + 2}. This takes into account the +two bytes needed for the escape sequences to single the switching. The +asymmetry in the maximum values for the two directions can be explained +easily: when reading ISO-2022-JP text escape sequences can be handled +alone. I.e., it is not necessary to process a real character since the +effect of the escape sequence can be recorded in the state information. +The situation is different for the other direction. Since it is in +general not known which character comes next one cannot emit escape +sequences to change the state in advance. This means the escape +sequences which have to be emitted together with the next character. +Therefore one needs more room then only for the character itself. + +The possible return values of the initialization function are: + +@table @code +@item GCONV_OK +The initialization succeeded +@item GCONV_NOCONV +The requested conversion is not supported in the module. This can +happen if the @file{gconv-modules} file has errors. +@item GCONV_NOMEM +Memory required to store additional information could not be allocated. +@end table +@end deftypevr + +The functions called before the module is unloaded is significantly +easier. It often has nothing at all to do in which case it can be left +out completely. + +@comment gconv.h +@comment GNU +@deftypevr {Data type} void (*gconv_end_fct) (struct gconv_step *) +The task of this function is it to free all resources allocated in the +initialization function. Therefore only the @code{data} element of the +object pointed to by the argument is of interest. Continuing the +example from the initialization function, the finalization function +looks like this: + +@smallexample +void +gconv_end (struct gconv_step *data) +@{ + free (data->data); +@} +@end smallexample +@end deftypevr + +The most important function of course is the conversion function itself. +It can get quite complicated for complex character sets. But since this +is not of interest here we will only describe a possible skeleton for +the conversion function. + +@comment gconv.h +@comment GNU +@deftypevr {Data type} int (*gconv_fct) (struct gconv_step *, struct gconv_step_data *, const char **, const char *, size_t *, int) +The conversion function can be called for two basic reason: to convert +text or to reset the state. From the description of the @code{iconv} +function it can be seen why the flushing mode is necessary. What mode +is selected is determined by the sixth argument, an integer. If it is +nonzero it means that flushing is selected. + +Common to both mode is where the output buffer can be found. The +information about this buffer is stored in the conversion step data. A +pointer to this is passed as the second argument to this function. The +description of the @code{struct gconv_step_data} structure has more +information on this. + +@cindex stateful +What has to be done for flushing depends on the source character set. +If it is not stateful nothing has to be done. Otherwise the function +has to emit a byte sequence to bring the state object in the initial +state. Once this all happened the other conversion modules in the chain +of conversions have to get the same chance. Whether another step +follows can be determined from the @code{is_last} element of the step +data structure to which the first parameter points. + +The more interesting mode is when actually text has to be converted. +The first step in this case is to convert as much text as possible from +the input buffer and store the result in the output buffer. The start +of the input buffer is determined by the third argument which is a +pointer to a pointer variable referencing the beginning of the buffer. +The fourth argument is a pointer to the byte right after the last byte +in the buffer. + +The conversion has to be performed according to the current state if the +character set is stateful. The state is stored in an object pointed to +by the @code{statep} element of the step data (second argument). Once +either the input buffer is empty or the output buffer is full the +conversion stops. At this point the pointer variable referenced by the +third parameter must point to the byte following the last processed +byte. I.e., if all of the input is consumed this pointer and the fourth +parameter have the same value. + +What now happens depends on whether this step is the last one or not. +If it is the last step the only thing which has to be done is to update +the @code{outbuf} element of the step data structure to point after the +last written byte. This gives the caller the information on how much +text is available in the output buffer. Beside this the variable +pointed to by the fifth parameter, which is of type @code{size_t}, must +be incremented by the number of characters (@emph{not bytes}) which were +written in the output buffer. Then the function can return. + +In case the step is not the last one the later conversion functions have +to get a chance to do their work. Therefore the appropriate conversion +function has to be called. The information about the functions is +stored in the conversion data structures, passed as the first parameter. +This information and the step data are stored in arrays so the next +element in both cases can be found by simple pointer arithmetic: + +@smallexample +int +gconv (struct gconv_step *step, struct gconv_step_data *data, + const char **inbuf, const char *inbufend, size_t *written, + int do_flush) +@{ + struct gconv_step *next_step = step + 1; + struct gconv_step_data *next_data = data + 1; + ... +@end smallexample + +The @code{next_step} pointer references the next step information and +@code{next_data} the next data record. The call of the next function +therefore will look similar to this: + +@smallexample + next_step->fct (next_step, next_data, &outerr, outbuf, written, 0) +@end smallexample + +But this is not yet all. Once the function call returns the conversion +function might have some more to do. If the return value of the +function is @code{GCONV_EMPTY_INPUT} this means there is more room in +the output buffer. Unless the input buffer is empty the conversion +functions start all over again and processes the rest of the input +buffer. If the return value is not @code{GCONV_EMPTY_INPUT} something +went wrong and we have to recover from this. + +A requirement for the conversion function is that the input buffer +pointer (the third argument) always points to the last character which +was put in the converted form in the output buffer. This is trivial +true after the conversion performed in the current step. But if the +conversion functions deeper down the stream stop prematurely not all +characters from the output buffer are consumed and therefore the input +buffer pointers must be backed of to the right position. + +This is easy to do if the input and output character sets have a fixed +width for all characters. In this situation we can compute how many +characters are left in the output buffer and therefore can correct the +input buffer pointer appropriate with a similar computation. Things are +getting tricky if either character set has character represented with +variable length byte sequences and it gets even more complicated if the +conversion has to take care of the state. In these cases the conversion +has to be performed once again, from the known state before the initial +conversion. I.e., if necessary the state of the conversion has to be +reset and the conversion loop has to be executed again. The difference +now is that it is known how much input must be created and the +conversion can stop before converting the first unused character. Once +this is done the input buffer pointers must be updated again and the +function can return. + +One final thing should be mentioned. If it is necessary for the +conversion to know whether it is the first invocation (in case a prolog +has to be emitted) the conversion function should just before returning +to the caller increment the @code{invocation_counter} element of the +step data structure. See the description of the @code{struct +gconv_step_data} structure above for more information on how this can be +used. + +The return value must be one of the following values: + +@table @code +@item GCONV_EMPTY_INPUT +All input was consumed and there is room left in the output buffer. +@item GCONV_OUTPUT_FULL +No more room in the output buffer. In case this is not the last step +this value is propagated down from the call of the next conversion +function in the chain. +@item GCONV_INCOMPLETE_INPUT +The input buffer is not entirely empty since it contains an incomplete +character sequence. +@end table + +The following example provides a framework for a conversion function. +In case a new conversion has to be written the holes in this +implementation have to be filled and that is it. + +@smallexample +int +gconv (struct gconv_step *step, struct gconv_step_data *data, + const char **inbuf, const char *inbufend, size_t *written, + int do_flush) +@{ + struct gconv_step *next_step = step + 1; + struct gconv_step_data *next_data = data + 1; + gconv_fct fct = next_step->fct; + int status; + + /* @r{If the function is called with no input this means we have} + @r{to reset to the initial state. The possibly partly} + @r{converted input is dropped.} */ + if (do_flush) + @{ + status = GCONV_OK; + + /* @r{Possible emit a byte sequence which put the state object} + @r{into the initial state.} */ + + /* @r{Call the steps down the chain if there are any but only} + @r{if we successfully emitted the escape sequence.} */ + if (status == GCONV_OK && ! data->is_last) + status = fct (next_step, next_data, NULL, NULL, + written, 1); + @} + else + @{ + /* @r{We preserve the initial values of the pointer variables.} */ + const char *inptr = *inbuf; + char *outbuf = data->outbuf; + char *outend = data->outbufend; + char *outptr; + + /* @r{This variable is used to count the number of characters} + @r{we actually converted.} */ + size_t converted = 0; + + do + @{ + /* @r{Remember the start value for this round.} */ + inptr = *inbuf; + /* @r{The outbuf buffer is empty.} */ + outptr = outbuf; + + /* @r{For stateful encodings the state must be safe here.} */ + + /* @r{Run the conversion loop. @code{status} is set} + @r{appropriately afterwards.} */ + + /* @r{If this is the last step leave the loop, there is} + @r{nothing we can do.} */ + if (data->is_last) + @{ + /* @r{Store information about how many bytes are} + @r{available.} */ + data->outbuf = outbuf; + + /* @r{Remember how many characters we converted.} */ + *written += converted; + + break; + @} + + /* @r{Write out all output which was produced.} */ + if (outbuf > outptr) + @{ + const char *outerr = data->outbuf; + int result; + + result = fct (next_step, next_data, &outerr, + outbuf, written, 0); + + if (result != GCONV_EMPTY_INPUT) + @{ + if (outerr != outbuf) + @{ + /* @r{Reset the input buffer pointer. We} + @r{document here the complex case.} */ + size_t nstatus; + + /* @r{Reload the pointers.} */ + *inbuf = inptr; + outbuf = outptr; + + /* @r{Possibly reset the state.} */ + + /* @r{Redo the conversion, but this time} + @r{the end of the output buffer is at} + @r{@code{outerr}.} */ + @} + + /* @r{Change the status.} */ + status = result; + @} + else + /* @r{All the output is consumed, we can make} + @r{ another run if everything was ok.} */ + if (status == GCONV_FULL_OUTPUT) + status = GCONV_OK; + @} + @} + while (status == GCONV_OK); + + /* @r{We finished one use of this step.} */ + ++data->invocation_counter; + @} + + return status; +@} +@end smallexample +@end deftypevr + +This information should be sufficient to write new modules. Anybody +doing so should also take a look at the available source code in the GNU +C library sources. It contains many examples of working and optimized +modules. diff --git a/manual/ctype.texi b/manual/ctype.texi index 26e40a1c53..de90acbe67 100644 --- a/manual/ctype.texi +++ b/manual/ctype.texi @@ -15,11 +15,20 @@ are affected by the current locale. (More precisely, they are affected by the locale currently selected for character classification---the @code{LC_CTYPE} category; see @ref{Locale Categories}.) -@menu -* Classification of Characters:: Testing whether characters are - letters, digits, punctuation, etc. +The @w{ISO C} standard specifies two different sets of functions. The +one set works on @code{char} type characters, the other one on +@code{wchar_t} wide character (@pxref{Extended Char Intro}). -* Case Conversion:: Case mapping, and the like. +@menu +* Classification of Characters:: Testing whether characters are + letters, digits, punctuation, etc. + +* Case Conversion:: Case mapping, and the like. +* Classification of Wide Characters:: Character class determination for + wide characters. +* Using Wide Char Classes:: Notes on using the wide character + classes. +* Wide Character Case Conversion:: Mapping of wide characters. @end menu @node Classification of Characters, Case Conversion, , Character Handling @@ -57,14 +66,16 @@ These functions are declared in the header file @file{ctype.h}. @comment ctype.h @comment ISO @deftypefun int islower (int @var{c}) -Returns true if @var{c} is a lower-case letter. +Returns true if @var{c} is a lower-case letter. The letter need not be +from the Latin alphabet, any alphabet representable is valid. @end deftypefun @cindex upper-case character @comment ctype.h @comment ISO @deftypefun int isupper (int @var{c}) -Returns true if @var{c} is an upper-case letter. +Returns true if @var{c} is an upper-case letter. The letter need not be +from the Latin alphabet, any alphabet representable is valid. @end deftypefun @cindex alphabetic character @@ -188,7 +199,7 @@ into the US/UK ASCII character set. This function is a BSD extension and is also an SVID extension. @end deftypefun -@node Case Conversion, , Classification of Characters, Character Handling +@node Case Conversion, Classification of Wide Characters, Classification of Characters, Character Handling @section Case Conversion @cindex character case conversion @cindex case conversion of characters @@ -224,7 +235,7 @@ lower-case letter. If @var{c} is not an upper-case letter, @comment ctype.h @comment ISO @deftypefun int toupper (int @var{c}) -If @var{c} is a lower-case letter, @code{tolower} returns the corresponding +If @var{c} is a lower-case letter, @code{toupper} returns the corresponding upper-case letter. Otherwise @var{c} is returned unchanged. @end deftypefun @@ -249,3 +260,497 @@ with the SVID. @xref{SVID}.@refill This is identical to @code{toupper}, and is provided for compatibility with the SVID. @end deftypefun + + +@node Classification of Wide Characters, Using Wide Char Classes, Case Conversion, Character Handling +@section Character class determination for wide characters + +The second amendment to @w{ISO C89} defines functions to classify wide +character. Although the original @w{ISO C89} standard already defined +the type @code{wchar_t} but no functions operating on them were defined. + +The general design of the classification functions for wide characters +is more general. It allows to extend the set of available +classification beyond the set which is always available. The POSIX +standard specifies a way how the extension can be done and this is +already implemented in the GNU C library implementation of the +@code{localedef} program. + +The character class functions are normally implemented using bitsets. +I.e., for the character in question the appropriate bitset is read from +a table and a test is performed whether a certain bit is set in this +bitset. Which bit is tested for is determined by the class. + +For the wide character classification functions this is made visible. +There is a type representing the classification, a function to retrieve +this value for a specific class, and a function to test using the +classification value whether a given character is in this class. On top +of this the normal character classification functions as used for +@code{char} objects can be defined. + +@comment wctype.h +@comment ISO +@deftp {Data type} wctype_t +The @code{wctype_t} can hold a value which represents a character class. +The ony defined way to generate such a value is by using the +@code{wctype} function. + +@pindex wctype.h +This type is defined in @file{wctype.h}. +@end deftp + +@comment wctype.h +@comment ISO +@deftypefun wctype_t wctype (const char *@var{property}) +The @code{wctype} returns a value representing a class of wide +characters which is identified by the string @var{property}. Beside +some standard properties each locale can define its own ones. In case +no property with the given name is known for the current locale for the +@code{LC_CTYPE} category the function returns zero. + +@noindent +The properties known in every locale are: + +@multitable @columnfractions .25 .25 .25 .25 +@item +@code{"alnum"} @tab @code{"alpha"} @tab @code{"cntrl"} @tab @code{"digit"} +@item +@code{"graph"} @tab @code{"lower"} @tab @code{"print"} @tab @code{"punct"} +@item +@code{"space"} @tab @code{"upper"} @tab @code{"xdigit"} +@end multitable + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +To test the membership of a character to one of the non-standard classes +the @w{ISO C} standard defines a completely new function. + +@comment wctype.h +@comment ISO +@deftypefun int iswctype (wint_t @var{wc}, wctype_t @var{desc}) +This function returns a nonzero value if @var{wc} is in the character +class specified by @var{desc}. @var{desc} must previously be returned +by a successful call to @code{wctype}. + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +The make it easier to use the commonly used classification functions +they are defined in the C library. There is no need to use +@code{wctype} is the property string is one of the known character +classes. In some situations it is desirable to construct the property +string and then it gets important that @code{wctype} can also handle the +standard classes. + +@cindex alphanumeric character +@comment wctype.h +@comment ISO +@deftypefun int iswalnum (wint_t @var{wc}) +This function returns a nonzero value if @var{wc} is an alphanumeric +character (a letter or number); in other words, if either @code{iswalpha} +or @code{iswdigit} is true of a character, then @code{iswalnum} is also +true. + +@noindent +This function can be implemented using + +@smallexample +iswctype (wc, wctype ("alnum")) +@end smallexample + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +@cindex alphabetic character +@comment wctype.h +@comment ISO +@deftypefun int iswalpha (wint_t @var{wc}) +Returns true if @var{wc} is an alphabetic character (a letter). If +@code{iswlower} or @code{iswupper} is true of a character, then +@code{iswalpha} is also true. + +In some locales, there may be additional characters for which +@code{iswalpha} is true---letters which are neither upper case nor lower +case. But in the standard @code{"C"} locale, there are no such +additional characters. + +@noindent +This function can be implemented using + +@smallexample +iswctype (wc, wctype ("alpha")) +@end smallexample + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +@cindex control character +@comment wctype.h +@comment ISO +@deftypefun int iswcntrl (wint_t @var{wc}) +Returns true if @var{wc} is a control character (that is, a character that +is not a printing character). + +@noindent +This function can be implemented using + +@smallexample +iswctype (wc, wctype ("cntrl")) +@end smallexample + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +@cindex digit character +@comment wctype.h +@comment ISO +@deftypefun int iswdigit (wint_t @var{wc}) +Returns true if @var{wc} is a digit (e.g., @samp{0} through @samp{9}). +Please note that this function does not only return a nonzero value for +@emph{decimal} digits, but for all kinds of digits. A consequence is +that code like the following will @strong{not} work unconditionally for +wide characters: + +@smallexample +n = 0; +while (iswctype (*wc)) + @{ + n *= 10; + n += *wc++ - L'0'; + @} +@end smallexample + +@noindent +This function can be implemented using + +@smallexample +iswctype (wc, wctype ("digit")) +@end smallexample + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +@cindex graphic character +@comment wctype.h +@comment ISO +@deftypefun int iswgraph (wint_t @var{wc}) +Returns true if @var{wc} is a graphic character; that is, a character +that has a glyph associated with it. The whitespace characters are not +considered graphic. + +@noindent +This function can be implemented using + +@smallexample +iswctype (wc, wctype ("graph")) +@end smallexample + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +@cindex lower-case character +@comment ctype.h +@comment ISO +@deftypefun int iswlower (wint_t @var{wc}) +Returns true if @var{wc} is a lower-case letter. The letter need not be +from the Latin alphabet, any alphabet representable is valid. + +@noindent +This function can be implemented using + +@smallexample +iswctype (wc, wctype ("lower")) +@end smallexample + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +@cindex printing character +@comment wctype.h +@comment ISO +@deftypefun int iswprint (wint_t @var{wc}) +Returns true if @var{wc} is a printing character. Printing characters +include all the graphic characters, plus the space (@samp{ }) character. + +@noindent +This function can be implemented using + +@smallexample +iswctype (wc, wctype ("print")) +@end smallexample + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +@cindex punctuation character +@comment wctype.h +@comment ISO +@deftypefun int iswpunct (wint_t @var{wc}) +Returns true if @var{wc} is a punctuation character. +This means any printing character that is not alphanumeric or a space +character. + +@noindent +This function can be implemented using + +@smallexample +iswctype (wc, wctype ("punct")) +@end smallexample + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +@cindex whitespace character +@comment wctype.h +@comment ISO +@deftypefun int iswspace (wint_t @var{wc}) +Returns true if @var{wc} is a @dfn{whitespace} character. In the standard +@code{"C"} locale, @code{iswspace} returns true for only the standard +whitespace characters: + +@table @code +@item L' ' +space + +@item L'\f' +formfeed + +@item L'\n' +newline + +@item L'\r' +carriage return + +@item L'\t' +horizontal tab + +@item L'\v' +vertical tab +@end table + +@noindent +This function can be implemented using + +@smallexample +iswctype (wc, wctype ("space")) +@end smallexample + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +@cindex upper-case character +@comment wctype.h +@comment ISO +@deftypefun int iswupper (wint_t @var{wc}) +Returns true if @var{wc} is an upper-case letter. The letter need not be +from the Latin alphabet, any alphabet representable is valid. + +@noindent +This function can be implemented using + +@smallexample +iswctype (wc, wctype ("upper")) +@end smallexample + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +@cindex hexadecimal digit character +@comment wctype.h +@comment ISO +@deftypefun int iswxdigit (wint_t @var{wc}) +Returns true if @var{wc} is a hexadecimal digit. +Hexadecimal digits include the normal decimal digits @samp{0} through +@samp{9} and the letters @samp{A} through @samp{F} and +@samp{a} through @samp{f}. + +@noindent +This function can be implemented using + +@smallexample +iswctype (wc, wctype ("xdigit")) +@end smallexample + +@pindex wctype.h +This function is declared in @file{wctype.h}. +@end deftypefun + +The GNu C library provides also a function which is not defined in the +@w{ISO C} standard but which is available as a version for single byte +characters as well. + +@cindex blank character +@comment wctype.h +@comment GNU +@deftypefun int iswblank (wint_t @var{wc}) +Returns true if @var{wc} is a blank character; that is, a space or a tab. +This function is a GNU extension. It is declared in @file{wchar.h}. +@end deftypefun + +@node Using Wide Char Classes, Wide Character Case Conversion, Classification of Wide Characters, Character Handling +@section Notes on using the wide character classes + +The first note is probably nothing astonishing but still occasionally a +cause of problems. The @code{isw@var{XXX}} functions can be implemented +using macros and in fact, the GNU C library does this. They are still +available as real functions but when the @file{wctype.h} header is +included the macros will be used. This is nothing new compared to the +@code{char} type versions of these functions. + +The second notes covers something which is new. It can be best +illustrated by a (real-world) example. The first piece of code is an +excerpt from the original code. It is truncated a bit but the intention +should be clear. + +@smallexample +int +is_in_class (int c, const char *class) +@{ + if (strcmp (class, "alnum") == 0) + return isalnum (c); + if (strcmp (class, "alpha") == 0) + return isalpha (c); + if (strcmp (class, "cntrl") == 0) + return iscntrl (c); + ... + return 0; +@} +@end smallexample + +Now with the @code{wctype} and @code{iswctype} one could avoid the +@code{if} cascades. But rewriting the code as follows is wrong: + +@smallexample +int +is_in_class (int c, const char *class) +@{ + wctype_t desc = wctype (class); + return desc ? iswctype ((wint_t) c, desc) : 0; +@} +@end smallexample + +The problem is that it is not guarateed that the wide character +representation of a single-byte character can be found using casting. +In fact, usually this fails miserably. The correct solution for this +problem is to write the code as follows: + +@smallexample +int +is_in_class (int c, const char *class) +@{ + wctype_t desc = wctype (class); + return desc ? iswctype (btowc (c), desc) : 0; +@} +@end smallexample + +See @xref{Converting a Character} for more information on @code{btowc}. +Please note that this change probably does not improve the performance +of the program a lot since the @code{wctype} function still has to make +the string comparisons. But it gets really interesting if the +@code{is_in_class} function would be called more than once using the +same class name. In this case the variable @var{desc} could be computed +once and reused for all the calls. Therefore the above form of the +function is probably not the final one. + + +@node Wide Character Case Conversion, , Using Wide Char Classes, Character Handling +@section Mapping of wide characters. + +As for the classification functions the @w{ISO C} standard also +generalizes the mapping functions. Instead of only allowing the two +standard mappings the locale can contain others. Again, the +@code{localedef} program already supports generating such locale data +files. + +@comment wctype.h +@comment ISO +@deftp {Data Type} wctrans_t +This data type is defined as a scalar type which can hold a value +representing the locale-dependent character mapping. There is no way to +construct such a value beside using the return value of the +@code{wctrans} function. + +@pindex wctype.h +@noindent +This type is defined in @file{wctype.h}. +@end deftp + +@comment wctype.h +@comment ISO +@deftypefun wctrans_t wctrans (const char *@var{property} +The @code{wctrans} function has to be used to find out whether a named +mapping is defined in the current locale selected for the +@code{LC_CTYPE} category. If the returned value is non-zero it can +afterwards be used in calls to @code{towctrans}. If the return value is +zero no such mapping is known in the current locale. + +Beside locale-specific mappings there are two mappings which are +guaranteed to be available in every locale: + +@multitable @columnfractions .5 .5 +@item +@code{"tolower"} @tab @code{"toupper"} +@end multitable + +@pindex wctype.h +@noindent +This function is declared in @file{wctype.h}. +@end deftypefun + +@comment wctype.h +@comment ISO +@deftypefun wint_t towctrans (wint_t @var{wc}, wctrans_t @var{desc}) +The @code{towctrans} function maps the input character @var{wc} +according to the rules of the mapping for which @var{desc} is an +descriptor and returns the so found value. The @var{desc} value must be +obtained by a successful call to @code{wctrans}. + +@pindex wctype.h +@noindent +This function is declared in @file{wctype.h}. +@end deftypefun + +The @w{ISO C} standard also defines for the generally available mappings +convenient shortcuts so that it is not necesary to call @code{wctrans} +for them. + +@comment wctype.h +@comment ISO +@deftypefun wint_t towlower (wint_t @var{wc}) +If @var{wc} is an upper-case letter, @code{towlower} returns the corresponding +lower-case letter. If @var{wc} is not an upper-case letter, +@var{wc} is returned unchanged. + +@pindex wctype.h +@noindent +This function is declared in @file{wctype.h}. +@end deftypefun + +@comment wctype.h +@comment ISO +@deftypefun wint_t towupper (wint_t @var{wc}) +If @var{wc} is a lower-case letter, @code{towupper} returns the corresponding +upper-case letter. Otherwise @var{wc} is returned unchanged. + +@pindex wctype.h +@noindent +This function is declared in @file{wctype.h}. +@end deftypefun + +The same warnings given in the last section for the use of the wide +character classiffication function applies here. It is not possible to +simply cast a @code{char} type value to a @code{wint_t} and use it as an +argument for @code{towctrans} calls. diff --git a/manual/filesys.texi b/manual/filesys.texi index a473560bf5..b00ca66c92 100644 --- a/manual/filesys.texi +++ b/manual/filesys.texi @@ -2696,8 +2696,8 @@ this file, you must remove the old file explicitly first. If you need to use a temporary file in your program, you can use the @code{tmpfile} function to open it. Or you can use the @code{tmpnam} -(better: @code{tmpnam_r}) function make a name for a temporary file and -then open it in the usual way with @code{fopen}. +(better: @code{tmpnam_r}) function to make a name for a temporary file and +then you can open it in the usual way with @code{fopen}. The @code{tempnam} function is like @code{tmpnam} but lets you choose what directory temporary files will go in, and something about what diff --git a/manual/intro.texi b/manual/intro.texi index 3d674ac15d..2ac893e316 100644 --- a/manual/intro.texi +++ b/manual/intro.texi @@ -652,7 +652,7 @@ and shell file name patterns, and for expanding words as the shell does. and CPU time, as well as functions for setting alarms and timers. @item -@ref{Extended Characters}, contains information about manipulating +@ref{Character Set Handling}, contains information about manipulating characters and strings using character sets larger than will fit in the usual @code{char} data type. diff --git a/manual/lang.texi b/manual/lang.texi index 4162d7febc..6de6256ad3 100644 --- a/manual/lang.texi +++ b/manual/lang.texi @@ -855,7 +855,7 @@ long long int} and @code{unsigned long long int}, respectively. @item WCHAR_MAX This is the maximum value that can be represented by a @code{wchar_t}. -@xref{Wide Char Intro}. +@xref{Extended Char Intro}. @end vtable The header file @file{limits.h} also defines some additional constants diff --git a/manual/libc.texinfo b/manual/libc.texinfo index a09d65fbc7..ee5ee051fe 100644 --- a/manual/libc.texinfo +++ b/manual/libc.texinfo @@ -19,7 +19,7 @@ @c sold 0.06/1.09, print run out 21may96 @set EDITION 0.08 DRAFT @set VERSION 2.1 Beta -@set UPDATED 17 Dec 1998 +@set UPDATED 11 Jan 1999 @set ISBN 1-882114-53-1 @ifinfo @@ -28,7 +28,7 @@ This file documents the GNU C library. This is Edition @value{EDITION}, last updated @value{UPDATED}, of @cite{The GNU C Library Reference Manual}, for Version @value{VERSION}. -Copyright (C) 1993, '94, '95, '96, '97, '98 Free Software Foundation, Inc. +Copyright (C) 1993, '94, '95, '96, '97, '98, '99 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice diff --git a/manual/locale.texi b/manual/locale.texi index 8b6f3fc235..6cfacbdb8c 100644 --- a/manual/locale.texi +++ b/manual/locale.texi @@ -1,4 +1,4 @@ -@node Locales, Message Translation, Extended Characters, Top +@node Locales, Message Translation, Character Set Handling, Top @c %MENU% The country and language can affect the behavior of library functions @chapter Locales and Internationalization @@ -42,7 +42,7 @@ following: @itemize @bullet @item What multibyte character sequences are valid, and how they are -interpreted (@pxref{Extended Characters}). +interpreted (@pxref{Character Set Handling}). @item Classification of which characters in the local character set are @@ -140,7 +140,7 @@ and @code{strxfrm}); see @ref{Collation Functions}. @item LC_CTYPE This category applies to classification and conversion of characters, and to multibyte and wide characters; -see @ref{Character Handling}, and @ref{Extended Characters}. +see @ref{Character Handling}, and @ref{Character Set Handling}. @comment locale.h @comment ISO diff --git a/manual/memory.texi b/manual/memory.texi index d55a4d4fc3..958e1d14c5 100644 --- a/manual/memory.texi +++ b/manual/memory.texi @@ -230,9 +230,8 @@ char * savestring (const char *ptr, size_t len) @{ register char *value = (char *) xmalloc (len + 1); - memcpy (value, ptr, len); value[len] = '\0'; - return value; + return (char *) memcpy (value, ptr, len); @} @end group @end smallexample diff --git a/manual/stdio.texi b/manual/stdio.texi index cf615e407d..1b9679f3bb 100644 --- a/manual/stdio.texi +++ b/manual/stdio.texi @@ -929,10 +929,10 @@ This section provides details about the precise syntax of conversion specifications that can appear in a @code{printf} template string. -Characters in the template string that are not part of a -conversion specification are printed as-is to the output stream. -Multibyte character sequences (@pxref{Extended Characters}) are permitted in -a template string. +Characters in the template string that are not part of a conversion +specification are printed as-is to the output stream. Multibyte +character sequences (@pxref{Character Set Handling}) are permitted in a +template string. The conversion specifications in a @code{printf} template string have the general form: diff --git a/manual/string.texi b/manual/string.texi index ae4ba659af..a35f3e979f 100644 --- a/manual/string.texi +++ b/manual/string.texi @@ -1,4 +1,4 @@ -@node String and Array Utilities, Extended Characters, Character Handling, Top +@node String and Array Utilities, Character Set Handling, Character Handling, Top @c %MENU% Utilities for copying and comparing strings and arrays @chapter String and Array Utilities diff --git a/manual/texis b/manual/texis index c62c558dc6..c6e72269eb 100644 --- a/manual/texis +++ b/manual/texis @@ -8,7 +8,7 @@ string.texi \ stpcpy.c.texi \ strdupa.c.texi \ strncat.c.texi \ -mbyte.texi \ +charset.texi \ locale.texi \ message.texi \ search.texi \ diff --git a/manual/top-menu.texi b/manual/top-menu.texi index 32ee478e2b..5f30407eed 100644 --- a/manual/top-menu.texi +++ b/manual/top-menu.texi @@ -6,7 +6,7 @@ * Character Handling:: Character testing and conversion functions. * String and Array Utilities:: Utilities for copying and comparing strings and arrays. -* Extended Characters:: Support for extended character sets. +* Character Set Handling:: Support for extended character sets. * Locales:: The country and language can affect the behavior of library functions. * Message Translation:: How to make the program speak the user's @@ -15,7 +15,7 @@ * Pattern Matching:: Matching shell ``globs'' and regular expressions. * I/O Overview:: Introduction to the I/O facilities. -* I/O on Streams:: Hign-level, portable I/O facilities. +* I/O on Streams:: High-level, portable I/O facilities. * Low-Level I/O:: Low-level, less portable I/O. * File System Interface:: Functions for manipulating files. * Pipes and FIFOs:: A simple interprocess communication @@ -45,6 +45,7 @@ Add-ons +* Cryptographic Functions:: DES encryption and password handling. * POSIX Threads:: The standard threads library. Appendices @@ -176,10 +177,15 @@ Variable Size Automatic Character Handling -* Classification of Characters:: Testing whether characters are - letters, digits, punctuation, etc. +* Classification of Characters:: Testing whether characters are + letters, digits, punctuation, etc. -* Case Conversion:: Case mapping, and the like. +* Case Conversion:: Case mapping, and the like. +* Classification of Wide Characters:: Character class determination for + wide characters. +* Using Wide Char Classes:: Notes on using the wide character + classes. +* Wide Character Case Conversion:: Mapping of wide characters. String and Array Utilities @@ -203,19 +209,40 @@ Argz and Envz Vectors * Argz Functions:: Operations on argz vectors. * Envz Functions:: Additional operations on environment vectors. -Extended Characters +Character Set Handling -* Extended Char Intro:: Multibyte codes versus wide characters. -* Locales and Extended Chars:: The locale selects the character codes. -* Multibyte Char Intro:: How multibyte codes are represented. -* Wide Char Intro:: How wide characters are represented. -* Wide String Conversion:: Converting wide strings to multibyte code - and vice versa. -* Length of Char:: how many bytes make up one multibyte char. -* Converting One Char:: Converting a string character by character. -* Example of Conversion:: Example showing why converting - one character at a time may be useful. -* Shift State:: Multibyte codes with "shift characters". +* Extended Char Intro:: Introduction to Extended Characters. +* Charset Function Overview:: Overview about Character Handling + Functions. +* Restartable multibyte conversion:: Restartable multibyte conversion + Functions. +* Non-reentrant Conversion:: Non-reentrant Conversion Function. +* Generic Charset Conversion:: Generic Charset Conversion. + +Restartable multibyte conversion + +* Selecting the Conversion:: Selecting the conversion and its properties. +* Keeping the state:: Representing the state of the conversion. +* Converting a Character:: Converting Single Characters. +* Converting Strings:: Converting Multibyte and Wide Character + Strings. +* Multibyte Conversion Example:: A Complete Multibyte Conversion Example. + +Non-reentrant Conversion + +* Non-reentrant Character Conversion:: Non-reentrant Conversion of Single + Characters. +* Non-reentrant String Conversion:: Non-reentrant Conversion of Strings. +* Shift State:: States in Non-reentrant Functions. + +Generic Charset Conversion + +* Generic Conversion Interface:: Generic Character Set Conversion Interface. +* iconv Examples:: A complete @code{iconv} example. +* Other iconv Implementations:: Some Details about other @code{iconv} + Implementations. +* glibc iconv Implementation:: The @code{iconv} Implementation in the GNU C + library. Locales @@ -751,6 +778,8 @@ Date and Time * Processor Time:: Measures processor time used by a program. * Calendar Time:: Manipulation of ``real'' dates and times. +* Precision Time:: Manipulation and monitoring of high accuracy + time. * Setting an Alarm:: Sending a signal after a specified time. * Sleeping:: Waiting for a period of time. * Resource Usage:: Measuring various resources used. @@ -1094,6 +1123,13 @@ Sysconf * Examples of Sysconf:: How to use @code{sysconf} and the parameter macros properly together. +Cryptographic Functions + +* Legal Problems:: This software can get you locked up, or worse. +* getpass:: Prompting the user for a password. +* crypt:: A one-way function for UNIX passwords. +* DES Encryption:: Routines for DES encryption. + POSIX Threads * Basic Thread Operations:: Creating, terminating, and waiting for threads. |