https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68737
--- Comment #16 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Yes I've just realised that passing 0 was a red herring, because we take the
#if _GLIBCXX_USE_C99_STDIO branch. Sorry.
I don't think __cs_size + 1 will be enough in general. There's no reason to
think it's only 1 byte too small.
Maybe we need a kluge like:
--- a/libstdc++-v3/include/bits/locale_facets.tcc
+++ b/libstdc++-v3/include/bits/locale_facets.tcc
@@ -1008,6 +1008,20 @@ _GLIBCXX_BEGIN_NAMESPACE_LDBL
__len = std::__convert_from_v(_S_get_c_locale(), __cs, __cs_size,
__fbuf, __v);
+#ifdef __hpux
+ while (__len == -1 && __cs_size < 1024)
+ {
+ __cs_size *= 2;
+ char* __cs = static_cast<char*>(__builtin_alloca(__cs_size));
+ if (__use_prec)
+ __len = std::__convert_from_v(_S_get_c_locale(), __cs, __cs_size,
+ __fbuf, __prec, __v);
+ else
+ __len = std::__convert_from_v(_S_get_c_locale(), __cs, __cs_size,
+ __fbuf, __v);
+ }
+#endif
+
// If the buffer was not large enough, try again with the correct size.
if (__len >= __cs_size)
{
