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author | Joseph Myers <joseph@codesourcery.com> | 2012-03-21 16:56:28 +0000 |
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committer | Joseph Myers <joseph@codesourcery.com> | 2012-03-21 16:56:28 +0000 |
commit | be22ce65d7643ffcd2dcb55b73eae4d7da6f0d71 (patch) | |
tree | 4d0e8f60788036ecdeff4caed7465ee733016485 /NOTES | |
parent | 40b601fbb774cd2be2f6cbe7155570340fc475a2 (diff) | |
download | glibc-be22ce65d7643ffcd2dcb55b73eae4d7da6f0d71.tar.gz glibc-be22ce65d7643ffcd2dcb55b73eae4d7da6f0d71.tar.xz glibc-be22ce65d7643ffcd2dcb55b73eae4d7da6f0d71.zip |
Remove NOTES.
Diffstat (limited to 'NOTES')
-rw-r--r-- | NOTES | 223 |
1 files changed, 0 insertions, 223 deletions
diff --git a/NOTES b/NOTES deleted file mode 100644 index 552f4cd609..0000000000 --- a/NOTES +++ /dev/null @@ -1,223 +0,0 @@ -Feature Test Macros -------------------- - -The exact set of features available when you compile a source file is -controlled by which "feature test macros" you define. - - If you compile your programs using `gcc -ansi', you get only the -ISO C library features, unless you explicitly request additional -features by defining one or more of the feature macros. *Note GNU CC -Command Options: (gcc.info)Invoking GCC, for more information about GCC -options. - - You should define these macros by using `#define' preprocessor -directives at the top of your source code files. These directives -_must_ come before any `#include' of a system header file. It is best -to make them the very first thing in the file, preceded only by -comments. You could also use the `-D' option to GCC, but it's better -if you make the source files indicate their own meaning in a -self-contained way. - - This system exists to allow the library to conform to multiple -standards. Although the different standards are often described as -supersets of each other, they are usually incompatible because larger -standards require functions with names that smaller ones reserve to the -user program. This is not mere pedantry -- it has been a problem in -practice. For instance, some non-GNU programs define functions named -`getline' that have nothing to do with this library's `getline'. They -would not be compilable if all features were enabled indiscriminately. - - This should not be used to verify that a program conforms to a -limited standard. It is insufficient for this purpose, as it will not -protect you from including header files outside the standard, or -relying on semantics undefined within the standard. - - -- Macro: _POSIX_SOURCE - If you define this macro, then the functionality from the POSIX.1 - standard (IEEE Standard 1003.1) is available, as well as all of the - ISO C facilities. - - The state of `_POSIX_SOURCE' is irrelevant if you define the macro - `_POSIX_C_SOURCE' to a positive integer. - - -- Macro: _POSIX_C_SOURCE - Define this macro to a positive integer to control which POSIX - functionality is made available. The greater the value of this - macro, the more functionality is made available. - - If you define this macro to a value greater than or equal to `1', - then the functionality from the 1990 edition of the POSIX.1 - standard (IEEE Standard 1003.1-1990) is made available. - - If you define this macro to a value greater than or equal to `2', - then the functionality from the 1992 edition of the POSIX.2 - standard (IEEE Standard 1003.2-1992) is made available. - - If you define this macro to a value greater than or equal to - `199309L', then the functionality from the 1993 edition of the - POSIX.1b standard (IEEE Standard 1003.1b-1993) is made available. - - Greater values for `_POSIX_C_SOURCE' will enable future extensions. - The POSIX standards process will define these values as necessary, - and the GNU C Library should support them some time after they - become standardized. The 1996 edition of POSIX.1 (ISO/IEC 9945-1: - 1996) states that if you define `_POSIX_C_SOURCE' to a value - greater than or equal to `199506L', then the functionality from - the 1996 edition is made available. - - -- Macro: _BSD_SOURCE - If you define this macro, functionality derived from 4.3 BSD Unix - is included as well as the ISO C, POSIX.1, and POSIX.2 material. - - Some of the features derived from 4.3 BSD Unix conflict with the - corresponding features specified by the POSIX.1 standard. If this - macro is defined, the 4.3 BSD definitions take precedence over the - POSIX definitions. - - Due to the nature of some of the conflicts between 4.3 BSD and - POSIX.1, you need to use a special "BSD compatibility library" - when linking programs compiled for BSD compatibility. This is - because some functions must be defined in two different ways, one - of them in the normal C library, and one of them in the - compatibility library. If your program defines `_BSD_SOURCE', you - must give the option `-lbsd-compat' to the compiler or linker when - linking the program, to tell it to find functions in this special - compatibility library before looking for them in the normal C - library. - - -- Macro: _SVID_SOURCE - If you define this macro, functionality derived from SVID is - included as well as the ISO C, POSIX.1, POSIX.2, and X/Open - material. - - -- Macro: _XOPEN_SOURCE - -- Macro: _XOPEN_SOURCE_EXTENDED - If you define this macro, functionality described in the X/Open - Portability Guide is included. This is a superset of the POSIX.1 - and POSIX.2 functionality and in fact `_POSIX_SOURCE' and - `_POSIX_C_SOURCE' are automatically defined. - - As the unification of all Unices, functionality only available in - BSD and SVID is also included. - - If the macro `_XOPEN_SOURCE_EXTENDED' is also defined, even more - functionality is available. The extra functions will make all - functions available which are necessary for the X/Open Unix brand. - - If the macro `_XOPEN_SOURCE' has the value 500 this includes all - functionality described so far plus some new definitions from the - Single Unix Specification, version 2. - - -- Macro: _LARGEFILE_SOURCE - If this macro is defined some extra functions are available which - rectify a few shortcomings in all previous standards. - Specifically, the functions `fseeko' and `ftello' are available. - Without these functions the difference between the ISO C interface - (`fseek', `ftell') and the low-level POSIX interface (`lseek') - would lead to problems. - - This macro was introduced as part of the Large File Support - extension (LFS). - - -- Macro: _LARGEFILE64_SOURCE - If you define this macro an additional set of functions is made - available which enables 32 bit systems to use files of sizes beyond - the usual limit of 2GB. This interface is not available if the - system does not support files that large. On systems where the - natural file size limit is greater than 2GB (i.e., on 64 bit - systems) the new functions are identical to the replaced functions. - - The new functionality is made available by a new set of types and - functions which replace the existing ones. The names of these new - objects contain `64' to indicate the intention, e.g., `off_t' vs. - `off64_t' and `fseeko' vs. `fseeko64'. - - This macro was introduced as part of the Large File Support - extension (LFS). It is a transition interface for the period when - 64 bit offsets are not generally used (see `_FILE_OFFSET_BITS'). - - -- Macro: _FILE_OFFSET_BITS - This macro determines which file system interface shall be used, - one replacing the other. Whereas `_LARGEFILE64_SOURCE' makes the - 64 bit interface available as an additional interface, - `_FILE_OFFSET_BITS' allows the 64 bit interface to replace the old - interface. - - If `_FILE_OFFSET_BITS' is undefined, or if it is defined to the - value `32', nothing changes. The 32 bit interface is used and - types like `off_t' have a size of 32 bits on 32 bit systems. - - If the macro is defined to the value `64', the large file interface - replaces the old interface. I.e., the functions are not made - available under different names (as they are with - `_LARGEFILE64_SOURCE'). Instead the old function names now - reference the new functions, e.g., a call to `fseeko' now indeed - calls `fseeko64'. - - This macro should only be selected if the system provides - mechanisms for handling large files. On 64 bit systems this macro - has no effect since the `*64' functions are identical to the - normal functions. - - This macro was introduced as part of the Large File Support - extension (LFS). - - -- Macro: _ISOC99_SOURCE - Until the revised ISO C standard is widely adopted the new features - are not automatically enabled. The GNU C Library nevertheless has - a complete implementation of the new standard and to enable the - new features the macro `_ISOC99_SOURCE' should be defined. - - -- Macro: _GNU_SOURCE - If you define this macro, everything is included: ISO C89, - ISO C99, POSIX.1, POSIX.2, BSD, SVID, X/Open, LFS, and GNU - extensions. In the cases where POSIX.1 conflicts with BSD, the - POSIX definitions take precedence. - - If you want to get the full effect of `_GNU_SOURCE' but make the - BSD definitions take precedence over the POSIX definitions, use - this sequence of definitions: - - #define _GNU_SOURCE - #define _BSD_SOURCE - #define _SVID_SOURCE - - Note that if you do this, you must link your program with the BSD - compatibility library by passing the `-lbsd-compat' option to the - compiler or linker. *NB:* If you forget to do this, you may get - very strange errors at run time. - - -- Macro: _REENTRANT - -- Macro: _THREAD_SAFE - If you define one of these macros, reentrant versions of several - functions get declared. Some of the functions are specified in - POSIX.1c but many others are only available on a few other systems - or are unique to the GNU C Library. The problem is the delay in - the standardization of the thread safe C library interface. - - Unlike on some other systems, no special version of the C library - must be used for linking. There is only one version but while - compiling this it must have been specified to compile as thread - safe. - - We recommend you use `_GNU_SOURCE' in new programs. If you don't -specify the `-ansi' option to GCC and don't define any of these macros -explicitly, the effect is the same as defining `_POSIX_C_SOURCE' to 2 -and `_POSIX_SOURCE', `_SVID_SOURCE', and `_BSD_SOURCE' to 1. - - When you define a feature test macro to request a larger class of -features, it is harmless to define in addition a feature test macro for -a subset of those features. For example, if you define -`_POSIX_C_SOURCE', then defining `_POSIX_SOURCE' as well has no effect. -Likewise, if you define `_GNU_SOURCE', then defining either -`_POSIX_SOURCE' or `_POSIX_C_SOURCE' or `_SVID_SOURCE' as well has no -effect. - - Note, however, that the features of `_BSD_SOURCE' are not a subset of -any of the other feature test macros supported. This is because it -defines BSD features that take precedence over the POSIX features that -are requested by the other macros. For this reason, defining -`_BSD_SOURCE' in addition to the other feature test macros does have an -effect: it causes the BSD features to take priority over the conflicting -POSIX features. - |