http://gcc.gnu.org/bugzilla/show_bug.cgi?id=47007
--- Comment #20 from Tobias Burnus <burnus at gcc dot gnu.org> ---
And yet another possibility: Some systems (like Darwin) have strtod_l (etc.)
which takes a locale argument. GLIBC seems to have it only as weak symbol but
offers __strtod_l.
Looking againt at GCC's C++ compiler, one finds in
libstdc++-v3/config/locale/gnu/c_locale.cc:
__v = __strtof_l(__s, &__sanity, __cloc);
#if __GLIBC__ > 2 || (__GLIBC__ == 2 && __GLIBC_MINOR__ > 2)
// Prefer strtold_l, as __strtold_l isn't prototyped in more recent
// glibc versions.
__v = strtold_l(__s, &__sanity, __cloc);
#else
__v = __strtold_l(__s, &__sanity, __cloc);
#endif
libstdc++ uses locale::facet::_S_get_c_locale() to get the locale.
The argument __cloc is in glibc/Darwin (->xlocate.h) __locale_t. However, the
symbol became official in POSIX 2008 and is now locale_t. Seemingly, one has to
obtain the locale with newlocale(..., "C",...) - and later should free it with
freelocale.
* * *
To summarize: It is probably best to use __strtold_l as C++ does, if it is
available. That should be the fastest, but requires that one caches the
locale_t var (e.g. get it at startup, free it at the end).
If it is not available, one presumably should use comment 19's method of
swapping the locale.
For libquadmath's strtoflt128, one either has to add an "_l" version - or one
has to always use the second method.
