strftime improvements

[Eric Blake]

Following up to my post last month about broken strftime(3), here is a
patch that implements all the remaining missing functionality required by
POSIX, as well as improving the documentation.

Note that there are still some useful non-POSIX extensions out there that
might be worth implementing.  In glibc, strftime(NULL, (size_t)UINT_MAX,
format, &tm) returns the number of characters that would be placed into a
non-NULL string, great for allocating a string to have exact length.  And
in Solaris, strftime(s, len, NULL, &tm) uses "%c" as the default format.

Also, something I did not know how to fix - POSIX requires that <time.h>
include extern int daylight, extern long timezone, and extern char
*tzname.  But as currently written, <time.h> has daylight and tzname
exposed only under __CYGWIN__, and timezone is a function instead of a
long unless timezonevar is defined.

2005-02-14  Eric Blake  <ebb9@byu.net>

	* libc/time/time.tex: Improve the documentation.
	* libc/time/strftime.c: Improve the documentation.
	(iso_year_adjust): New helper function.
	(strftime): Simplify '%E' and '%O'. Change '%c' to use
	recursion. Fix '%C', '%y', and '%Y' to deal with years with more
	than 4 characters.  Combine '%d' and '%e'. Implement '%D', '%F',
	'%g', '%G', '%n', '%R', '%t', '%T', '%u', '%V', '%X', and '%z'.
	Avoid core dumps on valid inputs (maxsize == 0, or
	tim_p->tm_isdst > 1).

-- 
Life is short - so eat dessert first!

Eric Blake             ebb9@byu.net
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