[Bug libstdc++/110653] Support std::stoi etc. without C99 APIs

["redi at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110653

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to dave.anglin from comment #3)
> On 2023-07-13 9:46 a.m., redi at gcc dot gnu.org wrote:
> > Dave, does this patch work for hppa64-hp-hpux11.11 ?
> Yes.

Great - pushed to trunk.

> On hpux, double and long double have different representations (they are
> same on linux).  hpux11.11 has both
> strtod and strtold.  strtold is checked for:
> 
> /* Define to 1 if you have the `strtof' function. */
> /* #undef HAVE_STRTOF */
> 
> /* Define to 1 if you have the `strtold' function. */
> #define HAVE_STRTOLD 1

Ah yes. That comes from libstdc++-v3/linkage.m4 which I think I've never even
looked at before!

> There doesn't seem to be a configure check for strtod.

That's from C89 and we already assume that's available unconditionally e.g. for
this code in <cstdlib>:

  using ::strtod;
  using ::strtol;
  using ::strtoul;


I'm testing this, which should define std::stof and std::stold for hpux11.11:

--- a/libstdc++-v3/include/bits/basic_string.h
+++ b/libstdc++-v3/include/bits/basic_string.h
@@ -4148,12 +4148,14 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
   stod(const string& __str, size_t* __idx = 0)
   { return __gnu_cxx::__stoa(&std::strtod, "stod", __str.c_str(), __idx); }

-#if _GLIBCXX_USE_C99_STDLIB
+#if _GLIBCXX_USE_C99_STDLIB || _GLIBCXX_HAVE_STRTOF
   // NB: strtof vs strtod.
   inline float
   stof(const string& __str, size_t* __idx = 0)
   { return __gnu_cxx::__stoa(&std::strtof, "stof", __str.c_str(), __idx); }
+#endif

+#if _GLIBCXX_USE_C99_STDLIB || _GLIBCXX_HAVE_STRTOLD
   inline long double
   stold(const string& __str, size_t* __idx = 0)
   { return __gnu_cxx::__stoa(&std::strtold, "stold", __str.c_str(), __idx); }
@@ -4161,7 +4163,7 @@ _GLIBCXX_BEGIN_NAMESPACE_CXX11
   inline long double
   stold(const string& __str, size_t* __idx = 0)
   { return std::stod(__str, __idx); }
-#endif // _GLIBCXX_USE_C99_STDLIB
+#endif

   // DR 1261. Insufficent overloads for to_string / to_wstring