[Bug libstdc++/103612] New: get_time parsing error for two digits year

[Bug libstdc++/103612] New: get_time parsing error for two digits year

[pyaggi at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103612

            Bug ID: 103612
           Summary: get_time parsing error for two digits year
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: pyaggi at gmail dot com
  Target Milestone: ---

std::get_time is behaving in the same way when the format includes '%y' or
'%Y', in both cases it tries to read a four digit year.

Example Code:
-------------
#include <iostream>
#include <iomanip>

void testDate(const char *format,const char *date)
{
    std::istringstream ds(date);
    std::tm tm = {};
    ds >> std::get_time(&tm,format);
    std::cout<<date<<" parsed using "<<format<<" -> Year: "<<tm.tm_year+1900<<"
Month: "<<tm.tm_mon<<" Day: "<<tm.tm_mday<<std::endl;
}

int main()
{
    testDate("%y%m%d","101112");
    testDate("%Y%m%d","101112");
    testDate("%y%m%d","20101112");
    testDate("%Y%m%d","20101112");

    return 0;
}

Output:
-------
101112 parsed using %y%m%d -> Year: 1011 Month: 11 Day: 0
101112 parsed using %Y%m%d -> Year: 1011 Month: 11 Day: 0
20101112 parsed using %y%m%d -> Year: 2010 Month: 10 Day: 12
20101112 parsed using %Y%m%d -> Year: 2010 Month: 10 Day: 12

Tested with:
------------
g++ (SUSE Linux) 11.2.1 20210816 
clang++ version 12.0.1

[Bug libstdc++/103612] get_time parsing error for two digits year

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103612

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=101152

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Dup of bug 101152 ?

[Bug libstdc++/103612] get_time parsing error for two digits year

[pyaggi at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103612

--- Comment #2 from Pablo <pyaggi at gmail dot com> ---
(In reply to Andrew Pinski from comment #1)
> Dup of bug 101152 ?

No, I don't think so. Here the problem is %y acts like %Y, it uses 4 digits of
the input, and It doesn't produce an error even in the case where there is not
enough digits to complete the parse.

[Bug libstdc++/103612] get_time parsing error for two digits year

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103612

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fsb4000 at yandex dot ru

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 105450 has been marked as a duplicate of this bug. ***

[Bug libstdc++/103612] get_time %y parsing error for two digits year

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103612

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=77760

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Looks like this actually might have gotten fixed for GCC 12. See bug #77760
comment #2 for the commit.

[Bug libstdc++/103612] get_time %y parsing error for two digits year

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103612

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
%y and %Y behave differently, %Y is always the full year, 0-9999, up to 4
digits.
%y is if 0-99, up to 2 digits using the POSIX rules 0-68 is 2000 to 2068, 69-99
is 1969 to 1999, but intentionally for backwards compatibility if it is
actually 3 or 4 digits, it is treated as %Y because that is how libstdc++ has
been treating it for years.

[Bug libstdc++/103612] get_time %y parsing error for two digits year

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103612

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Note, the above is GCC 12 behavior, in 11.x and earlier it has been indeed
broken and %y and %C were aliases to %Y.