Windows strftime issue

[shirolimit]

There is a problem with time formatting on Windows. Sometimes it can throw SEH exception.

The problem is in CRT strftime implementation, which fmtlib uses for time formatting.
Code from https://github.com/fmtlib/fmt/blob/master/include/fmt/time.h#L358

std::size_t size = buf.capacity() - start;
std::size_t count =
internal::strftime(&buf[start], size, &tm_format[0], &tm);

If the size of the buffer equals it's capacity, so that the value of size variable results in 0, then CRT throws SEH exception.

The reason is that MS implementation checks validity of the second parameter of strftime function (it is not standard compliant, btw, so maybe they'll fix).

Code snippet from MS strftime implementation:

extern "C" size_t __cdecl _Strftime_l (
    _Out_writes_z_(maxsize) char * const string,
    _In_ size_t                    const maxsize,
    _In_z_ const char *            const format,
    _In_ const tm *                const timeptr,
    _In_ void *                    const lc_time_arg,
    _In_opt_ _locale_t             const locale
    )
{
    _LocaleUpdate locale_update(locale);
    unsigned int const lc_time_cp = locale_update.GetLocaleT()->locinfo->lc_time_cp;

    _VALIDATE_RETURN(string != nullptr, EINVAL, 0)
    _VALIDATE_RETURN(maxsize != 0,      EINVAL, 0)

Possible fixes:

1. check for zero buffer size prior to strftime call
2. set invalid parameter handler via _set_invalid_parameter_handler, to avoid SEH exceptions (bad idea, cause it also need to store previous one, and could be replaced)

[vitaut]

Implemented a workaround in acfa95d, thanks for reporting.