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Diffstat (limited to 'manual/time.texi')
| -rw-r--r-- | manual/time.texi | 37 |
1 files changed, 21 insertions, 16 deletions
diff --git a/manual/time.texi b/manual/time.texi index 767c318a42..3f8eee46a3 100644 --- a/manual/time.texi +++ b/manual/time.texi @@ -241,13 +241,15 @@ These facilities are declared in the header file @file{time.h}. @comment time.h @comment ANSI @deftp {Data Type} time_t -This is the data type used to represent calendar time. In the GNU C -library and other POSIX-compliant implementations, @code{time_t} is -equivalent to @code{long int}. When interpreted as an absolute time +This is the data type used to represent calendar time. +When interpreted as an absolute time value, it represents the number of seconds elapsed since 00:00:00 on January 1, 1970, Coordinated Universal Time. (This date is sometimes -referred to as the @dfn{epoch}.) +referred to as the @dfn{epoch}.) POSIX requires that this count +ignore leap seconds, but on some hosts this count includes leap seconds +if you set @code{TZ} to certain values (@pxref{TZ Variable}). +In the GNU C library, @code{time_t} is equivalent to @code{long int}. In other systems, @code{time_t} might be either an integer or floating-point type. @end deftp @@ -257,7 +259,8 @@ floating-point type. @deftypefun double difftime (time_t @var{time1}, time_t @var{time0}) The @code{difftime} function returns the number of seconds elapsed between time @var{time1} and time @var{time0}, as a value of type -@code{double}. +@code{double}. The difference ignores leap seconds unless leap +second support is enabled. In the GNU system, you can simply subtract @code{time_t} values. But on other systems, the @code{time_t} data type might use some other encoding @@ -462,8 +465,8 @@ contains at least the following members, which can appear in any order: @table @code @item int tm_sec This is the number of seconds after the minute, normally in the range -@code{0} to @code{59}. (The actual upper limit is @code{61}, to allow -for ``leap seconds''.) +@code{0} to @code{59}. (The actual upper limit is @code{60}, to allow +for leap seconds if leap second support is available.) @cindex leap second @item int tm_min @@ -508,7 +511,7 @@ also think of this as the ``number of seconds west'' of GMT. The @code{tm_gmtoff} field is a GNU library extension. @item const char *tm_zone -This field is the three-letter name for the time zone that was used to +This field is the name for the time zone that was used to compute this broken-down time value. It is a GNU library extension. @end table @end deftp @@ -521,9 +524,9 @@ The @code{localtime} function converts the calendar time pointed to by user's specified time zone. The return value is a pointer to a static broken-down time structure, which -might be overwritten by subsequent calls to any of the date and time -functions. (But no other library function overwrites the contents of this -object.) +might be overwritten by subsequent calls to @code{ctime}, @code{gmtime}, +or @code{localtime}. (But no other library function overwrites the contents +of this object.) Calling @code{localtime} has one other effect: it sets the variable @code{tzname} with information about the current time zone. @xref{Time @@ -590,7 +593,7 @@ The abbreviations for the months are: @samp{Jan}, @samp{Feb}, @samp{Sep}, @samp{Oct}, @samp{Nov}, and @samp{Dec}. The return value points to a statically allocated string, which might be -overwritten by subsequent calls to any of the date and time functions. +overwritten by subsequent calls to @code{asctime} or @code{ctime}. (But no other library function overwrites the contents of this string.) @end deftypefun @@ -870,7 +873,7 @@ community of volunteers and put in the public domain. @comment POSIX.1 @deftypevar char * tzname [2] The array @code{tzname} contains two strings, which are the standard -three-letter names of the pair of time zones (standard and daylight +names of the pair of time zones (standard and daylight savings) that the user has selected. @code{tzname[0]} is the name of the standard time zone (for example, @code{"EST"}), and @code{tzname[1]} is the name for the time zone when daylight savings time is in use (for @@ -893,7 +896,7 @@ depend on the time zone. @end deftypefun The following variables are defined for compatibility with System V -Unix. These variables are set by calling @code{localtime}. +Unix. These variables are set by calling @code{tzset}. @comment time.h @comment SVID @@ -906,8 +909,10 @@ seconds. For example, in the U.S. Eastern time zone, the value is @comment time.h @comment SVID @deftypevar int daylight -This variable has a nonzero value if the standard U.S. daylight savings -time rules apply. +This variable has a nonzero value if daylight savings time rules apply. +A nonzero value does not necessarily mean that daylight savings time is +now in effect; it means only that daylight savings time is sometimes in +effect. @end deftypevar @node Time Functions Example |