+2023-02-05 Paul Eggert <eggert@cs.ucla.edu>
+
+ c-nullptr: new module
+ * doc/gnulib.texi (nullptr): New section.
+ * doc/posix-headers/stddef.texi: Document lack of nullptr_t.
+ * m4/c-nullptr.m4, modules/c-nullptr: New files.
+
2023-02-05 Bruno Haible <bruno@clisp.org>
Update build-aux/po/Makefile.in.in.
@menu
* alignof:: @code{alignas} and @code{alignof}
* bool:: @code{bool}, @code{false}, and @code{true}
+* nullptr:: @code{nullptr}
* static_assert:: @code{static_assert}
@end menu
On pre-C23 platforms, the keyword substitutes assume C99 or later.
@end itemize
+@node nullptr
+@section @code{nullptr}
+
+Gnulib module: c-nullptr
+
+@cindex null pointer
+The @code{c-nullptr} module arranges for @code{nullptr} to act
+like standard C@.
+
+The C @code{nullptr} keyword yields a null pointer. It differs from
+the @code{NULL} macro, in that @code{NULL} might be an integer whereas
+@code{nullptr} is of a special @code{nullptr_t} type with only one
+value, namely @code{nullptr} itself. Using @code{nullptr} can help
+some compilers emit more sensible warnings, can avoid the need to cast
+a null pointer passed to a function prototyped with an ellipsis, and
+removes the need to include @code{<stddef.h>} merely to define
+@code{NULL}.
+
+Portability problems fixed by Gnulib:
+@itemize
+@item
+Some platforms lack @code{nullptr}:
+GCC 12, Clang 15, and other pre-2023 C compilers.
+@end itemize
+
+Portability problems not fixed by Gnulib:
+@itemize
+@item
+On older platforms, @code{nullptr} is a macro instead of a keyword.
+
+@item
+On older platforms, @code{nullptr} does not have the type @code{nullptr_t}.
+In C, it has type @code{void *}; in C++ it has an integer type.
+
+@item
+On older platforms Gnulib cannot easily emulate @code{nullptr_t}, so
+null pointer type checking is more error prone, and @code{_Generic}
+expressions cannot reliably distinguish @code{nullptr}'s type from
+integer or @code{void *} types.
+@end itemize
+
@node static_assert
@section @code{static_assert}
Portability problems not fixed by Gnulib:
@itemize
+@item
+@cindex null pointer type
+Some platforms fail to provide @code{nullptr_t},
+which Gnulib cannot usefully emulate:
+GCC 12, Clang 15, and other pre-2023 C compilers.
+
@item
Some platforms provide an @code{offsetof} macro that cannot be used in
arbitrary expressions:
--- /dev/null
+# Check for nullptr that conforms to C23.
+
+dnl Copyright 2023 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+AC_DEFUN([gl_C_NULLPTR],
+[
+ AC_CACHE_CHECK([for nullptr], [gl_cv_c_nullptr],
+ [AC_COMPILE_IFELSE(
+ [AC_LANG_SOURCE([[int *p = nullptr;]])],
+ [gl_cv_c_nullptr=yes],
+ [gl_cv_c_nullptr=no])])
+ if test "$gl_cv_c_nullptr" = yes; then
+ AC_DEFINE([HAVE_C_NULLPTR], [1], [Define to 1 if nullptr works.])
+ fi
+])
+
+ AH_VERBATIM([nullptr],
+[#ifndef HAVE_C_NULLPTR
+# ifndef __cplusplus
+# define nullptr ((void *) 0)
+# elif 3 <= __GNUG__
+# define nullptr __null
+# else
+# define nullptr 0L
+# endif
+#endif])
+])