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authorPaul Eggert <eggert@cs.ucla.edu>2013-12-04 13:17:13 +0100
committerOndřej Bílka <neleai@seznam.cz>2013-12-04 13:21:27 +0100
commitfbf964ae8b52fb10ebe5f43996f53ddab53c08ed (patch)
tree3f3159fe1be4eb26b435cf15e148aea16876876c /manual
parentfa60a674885aa45cbe8a3c03d6e5386ba6d0ec5f (diff)
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Clarify documentation on how functions use timezone. Fixes bug 926.
Diffstat (limited to 'manual')
-rw-r--r--manual/time.texi38
1 files changed, 21 insertions, 17 deletions
diff --git a/manual/time.texi b/manual/time.texi
index ff31e28..1a5aaed 100644
--- a/manual/time.texi
+++ b/manual/time.texi
@@ -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