c32tob: New module.

* lib/uchar.in.h (_GL_LARGE_CHAR32_T): New macro.
(c32tob): New declaration.
* lib/c32tob.c: New file.
* m4/uchar.m4 (gl_UCHAR_MODULE_INDICATOR, gl_UCHAR_H_DEFAULTS): New
macros.
(gl_UCHAR_H): Require gl_UCHAR_H_DEFAULTS.
* modules/uchar (Depends-on): Add snippet/c++defs.
(Makefile.am): Include c++defs.h and substitute GNULIB_C32TOB in
uchar.h.
* modules/c32tob: New file.
* tests/test-uchar.c: Verify that _GL_LARGE_CHAR32_T is correctly
defined.
* tests/test-uchar-c++.cc: Include signature.h. Test the signature of
c32tob.
* modules/uchar-c++-tests (Files): Add tests/signature.h.
* doc/posix-functions/wctob.texi: Mention the new module.

1 files changed, 37 insertions, 0 deletions

diff --git a/lib/c32tob.c b/lib/c32tob.c
new file mode 100644
index 0000000000..e9db7a1a98
--- /dev/null
+++ b/lib/c32tob.c
@@ -0,0 +1,37 @@
+/* Convert 32-bit wide character to unibyte character.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+
+   This program is free software: you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+/* Written by Bruno Haible <bruno@clisp.org>, 2020.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <uchar.h>
+
+int
+c32tob (wint_t wc)
+{
+#if _GL_LARGE_CHAR32_T
+  /* In all known encodings, unibyte characters correspond only to
+     characters in the BMP.  */
+  if (wc != WEOF && (wchar_t) wc == wc)
+    return wctob ((wchar_t) wc);
+  else
+    return EOF;
+#else
+  return wctob (wc);
+#endif
+}