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Improve doc for time_t range (BZ 31808)

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Paul Eggert 2024-05-28 10:07:47 -07:00
parent cafef3eb21
commit 400bdb5c85
1 changed files with 11 additions and 1 deletions
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manual/time.texi
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@ -123,7 +123,7 @@ The number of clock ticks per second is system-specific.
@code{time_t} is the simplest data type used to represent simple
calendar time.
In ISO C, @code{time_t} can be either an integer or a floating-point
In ISO C, @code{time_t} can be either an integer or a real floating
type, and the meaning of @code{time_t} values is not specified. The
only things a strictly conforming program can do with @code{time_t}
values are: pass them to @code{difftime} to get the elapsed time
@ -134,11 +134,21 @@ and pass them to the functions that convert them to broken-down time
On POSIX-conformant systems, @code{time_t} is an integer type and its
values represent the number of seconds elapsed since the @dfn{epoch},
which is 00:00:00 on January 1, 1970, Coordinated Universal Time.
The count of seconds ignores leap seconds.
@Theglibc{} additionally guarantees that @code{time_t} is a signed
type, and that all of its functions operate correctly on negative
@code{time_t} values, which are interpreted as times before the epoch.
Functions like @code{localtime} assume the Gregorian calendar even
though this is historically inaccurate for timestamps before the
calendar was introduced or after the calendar will become obsolete.
@cindex epoch
@Theglibc{} also supports leap seconds as an option, in which case
@code{time_t} counts leap seconds instead of ignoring them.
Currently the @code{time_t} type is 64 bits wide on all platforms
supported by @theglibc{}, except that it is 32 bits wide on a few
older platforms unless you define @code{_TIME_BITS} to 64.
@xref{Feature Test Macros}.
@end deftp
@deftp {Data Type} {struct timespec}