[Bug libstdc++/78714] New: std::get_time does not accept full month name in %b

[cubbi at cubbi dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78714

            Bug ID: 78714
           Summary: std::get_time does not accept full month name in %b
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: cubbi at cubbi dot org
  Target Milestone: ---

The standard says time_get calls get_time which follows "ISO/IEC 9945 function
strptime" ([locale.time.get.members]p8.4)

strptime defines the meaning of %b as "The month, using the locale's month
names; either the abbreviated or full name may be specified.":
http://pubs.opengroup.org/onlinepubs/9699919799/functions/strptime.html

however it appears libstdc++ only accepts abbreviated month name:
https://github.com/gcc-mirror/gcc/blob/master/libstdc%2B%2B-v3/include/bits/locale_facets_nonio.tcc#L673-L678

testcase:

#include <iostream>
#include <sstream>
#include <cassert>
#include <iomanip>
#include <time.h>

tm t;
int main()
{
    assert(strptime("2011-Feb-18 23:12:34", "%Y-%b-%d %H:%M:%S", &t)); // pass
    assert(strptime("2011-February-18 23:12:34", "%Y-%b-%d %H:%M:%S", &t)); //
pass
    {
      std::istringstream ss("2011-Feb-18 23:12:34");
      assert(ss >> std::get_time(&t, "%Y-%b-%d %H:%M:%S")); // pass
    }
    {
      std::istringstream ss("2011-February-18 23:12:34");
      assert(ss >> std::get_time(&t, "%Y-%b-%d %H:%M:%S")); // FAIL
    }
}

all asserts pass with clang's libc++ and with MSVC 2015