[libcxx] [Windows] Use the standard vsnprintf instead of _vsnprintf

[mstorsjo]

Summary

In ancient Microsoft C runtimes, there might only have been
a nonstandard _vsnprintf instead of the standard vsnprintf, but
in modern versions (the only ones relevant for libc++), both
are available.

In MinGW configurations built with __USE_MINGW_ANSI_STDIO=1 (as it
is built in CI), vsnprintf provides a more standards compliant
behaviour than what Microsoft's CRT provides, while _vsnprintf retains
the Microsoft C runtime specific quirks.

[• Quuxplusone]

libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_double.pass.cpp

15–18

Is this XFAIL related to the "Microsoft C runtime specific quirks" you mention? It could use a comment to explain why we need to XFAIL here.

[ldionne]

libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_double.pass.cpp

15–18

Yeah, agreed, but otherwise LGTM.

[mstorsjo]

libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_double.pass.cpp

15–18

Yes, it’s the same kind of quirks.

I have later follow-up patches to sort out exactly what these quirks are and try to make the test runnable in that mode, so I left out those details from this patch though.

But I can leave a fixme comment to make it clear that we’re not done here.

libcxx/src/support/win32/support.cpp

 // a pointer to a malloc'd string in *sptr.
 // If return >= 0, use free to delete *sptr.
 int __libcpp_vasprintf( char **sptr, const char *__restrict format, va_list ap )
 {
     *sptr = NULL;
     // Query the count required.
     va_list ap_copy;
     va_copy(ap_copy, ap);
-    int count = _vsnprintf( NULL, 0, format, ap_copy );
+    int count = vsnprintf( NULL, 0, format, ap_copy );
     va_end(ap_copy);
     if (count < 0)
         return count;
     size_t buffer_size = static_cast<size_t>(count) + 1;
     char* p = static_cast<char*>(malloc(buffer_size));
     if ( ! p )
         return -1;
     // If we haven't used exactly what was required, something is wrong.
     // Maybe bug in vsnprintf. Report the error and return.
-    if (_vsnprintf(p, buffer_size, format, ap) != count) {
+    if (vsnprintf(p, buffer_size, format, ap) != count) {
         free(p);
         return -1;
     }
     // All good. This is returning memory to the caller not freeing it.
     *sptr = p;
     return count;
 }
 

libcxx/test/std/localization/locale.categories/category.numeric/locale.nm.put/facet.num.put.members/put_double.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // <locale>
 
 // class num_put<charT, OutputIterator>
 
 // iter_type put(iter_type s, ios_base& iob, char_type fill, double v) const;
 
-// XFAIL: LIBCXX-WINDOWS-FIXME
+// FIXME: The printf functions in Microsoft's CRT have a couple quirks in
+// corner cases, failing this test.
+// XFAIL: msvc
+
 // XFAIL: LIBCXX-AIX-FIXME
 
 #include <locale>
 #include <ios>
 #include <cassert>
 #include <streambuf>
 #include <cmath>
 #include "test_macros.h"