[PATCH] #undef isblank before def or decl in libstdc++ headers

[Jonathan Wakely]

On Fri, 10 Dec 2021 at 17:07, Olivier Hainque via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Hello,
>
> The attached patch helps fix a build failure of libstdc++
> on some variants of VxWorks where the system headers expose
> an "isblank" macro.
>
> I understand this kind of thing normally is handled through
> fixincludes, however fixincludes on VxWorks is very tricky and
> we already have
>
>   libstdc++-v3/include/c_global/cctype:#undef isblank
>   libstdc++-v3/include/tr1/cctype:#undef isblank
>
> so the suggestion here is to simply do the same in a couple
> more places.

Both of those places already include <cctype> so I think we should just do this:

--- a/libstdc++-v3/include/c_global/cctype
+++ b/libstdc++-v3/include/c_global/cctype
@@ -78,10 +78,10 @@ namespace std

#if __cplusplus >= 201103L

-#ifdef _GLIBCXX_USE_C99_CTYPE_TR1
-
#undef isblank

+#ifdef _GLIBCXX_USE_C99_CTYPE_TR1
+
namespace std
{
  using ::isblank;

I'm curious why _GLIBCXX_USE_C99_CTYPE_TR1 is not defined if VxWorks
has isblank, the configure check is:

  # Check for the existence of <ctype.h> functions.
  AC_CACHE_CHECK([for ISO C99 support to TR1 in <ctype.h>],
  glibcxx_cv_c99_ctype_tr1, [
  AC_TRY_COMPILE([#include <ctype.h>],
         [int ch;
          int ret;
          ret = isblank(ch);
         ],[glibcxx_cv_c99_ctype_tr1=yes],
           [glibcxx_cv_c99_ctype_tr1=no])
  ])
  if test x"$glibcxx_cv_c99_ctype_tr1" = x"yes"; then
    AC_DEFINE(_GLIBCXX_USE_C99_CTYPE_TR1, 1,
          [Define if C99 functions in <ctype.h> should be imported in
          <tr1/cctype> in namespace std::tr1.])
  fi

In any case, undef'ing it unconditionally in <cctype> should work, and
avoids having to do it in multiple places (we still need it in
<tr1/cctype> because that is used in C++98 code, whereas the other
definitions of functions called "isblank" were added for C++11).