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Clarify documentation on how functions use timezone. Fixes bug 926.

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Paul Eggert 2013-12-04 13:17:13 +01:00 committed by Ondřej Bílka
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ChangeLog
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@ -1,3 +1,9 @@
2013-12-04 Paul Eggert <eggert@cs.ucla.edu>
[BZ #926]
* manual/time.texi (Calendar Time): Clarify what timezone functions
use.
2013-12-04 Adhemerval Zanella <azanella@linux.vnet.ibm.com>
* sysdeps/powerpc/fpu/libm-test-ulps: Update.

38
manual/time.texi
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@ -687,9 +687,8 @@ The return value is the null pointer if @var{time} cannot be represented
as a broken-down time; typically this is because the year cannot fit into
an @code{int}.
Calling @code{localtime} has one other effect: it sets the variable
@code{tzname} with information about the current time zone. @xref{Time
Zone Functions}.
Calling @code{localtime} also sets the current time zone as if
@code{tzset} were called. @xref{Time Zone Functions}.
@end deftypefun
Using the @code{localtime} function is a big problem in multi-threaded
@ -739,25 +738,28 @@ object the result was written into, i.e., it returns @var{resultp}.
@comment time.h
@comment ISO
@deftypefun time_t mktime (struct tm *@var{brokentime})
The @code{mktime} function is used to convert a broken-down time structure
to a simple time representation. It also ``normalizes'' the contents of
the broken-down time structure, by filling in the day of week and day of
year based on the other date and time components.
The @code{mktime} function converts a broken-down time structure to a
simple time representation. It also normalizes the contents of the
broken-down time structure, and fills in some components based on the
values of the others.
The @code{mktime} function ignores the specified contents of the
@code{tm_wday} and @code{tm_yday} members of the broken-down time
@code{tm_wday}, @code{tm_yday}, @code{tm_gmtoff}, and @code{tm_zone}
members of the broken-down time
structure. It uses the values of the other components to determine the
calendar time; it's permissible for these components to have
unnormalized values outside their normal ranges. The last thing that
@code{mktime} does is adjust the components of the @var{brokentime}
structure (including the @code{tm_wday} and @code{tm_yday}).
structure, including the members that were initally ignored.
If the specified broken-down time cannot be represented as a simple time,
@code{mktime} returns a value of @code{(time_t)(-1)} and does not modify
the contents of @var{brokentime}.
Calling @code{mktime} also sets the variable @code{tzname} with
information about the current time zone. @xref{Time Zone Functions}.
Calling @code{mktime} also sets the current time zone as if
@code{tzset} were called; @code{mktime} uses this information instead
of @var{brokentime}'s initial @code{tm_gmtoff} and @code{tm_zone}
members. @xref{Time Zone Functions}.
@end deftypefun
@comment time.h
@ -1053,8 +1055,8 @@ rather than in broken-down local time format. It is equivalent to
asctime (localtime (@var{time}))
@end smallexample
@code{ctime} sets the variable @code{tzname}, because @code{localtime}
does so. @xref{Time Zone Functions}.
Calling @code{ctime} also sets the current time zone as if
@code{tzset} were called. @xref{Time Zone Functions}.
@end deftypefun
@comment time.h
@ -1081,7 +1083,8 @@ This function is similar to the @code{sprintf} function (@pxref{Formatted
Input}), but the conversion specifications that can appear in the format
template @var{template} are specialized for printing components of the date
and time @var{brokentime} according to the locale currently specified for
time conversion (@pxref{Locales}).
time conversion (@pxref{Locales}) and the current time zone
(@pxref{Time Zone Functions}).
Ordinary characters appearing in the @var{template} are copied to the
output string @var{s}; this can include multibyte character sequences.
@ -1392,9 +1395,10 @@ if (len == 0 && buf[0] != '\0')
If @var{s} is a null pointer, @code{strftime} does not actually write
anything, but instead returns the number of characters it would have written.
According to POSIX.1 every call to @code{strftime} implies a call to
@code{tzset}. So the contents of the environment variable @code{TZ}
is examined before any output is produced.
Calling @code{strftime} also sets the current time zone as if
@code{tzset} were called; @code{strftime} uses this information
instead of @var{brokentime}'s @code{tm_gmtoff} and @code{tm_zone}
members. @xref{Time Zone Functions}.
For an example of @code{strftime}, see @ref{Time Functions Example}.
@end deftypefun