--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2011-02-05  Bruno Haible  <bruno@clisp.org>
+
+	New module 'wcsnlen'.
+	* modules/wcsnlen: New file.
+	* lib/wchar.in.h (wcsnlen): New declaration.
+	* lib/wcsnlen.c: New file.
+	* lib/wcsnlen-impl.h: New file, from libutf8 with modifications.
+	* m4/wcsnlen.m4: New file.
+	* m4/wchar_h.m4 (gl_WCHAR_H): Test whether wcsnlen is declared.
+	(gl_WCHAR_H_DEFAULTS): Initialize GNULIB_WCSNLEN, HAVE_WCSNLEN.
+	* modules/wchar (Makefile.am): Substitute GNULIB_WCSNLEN, HAVE_WCSNLEN.
+	* tests/test-wchar-c++.cc: Test the declaration of wcsnlen.
+	* doc/posix-functions/wcsnlen.texi: Mention the new module.
+
 2011-02-05  Bruno Haible  <bruno@clisp.org>
 
 	New module 'wcslen'.

--- a/doc/posix-functions/wcsnlen.texi
+++ b/doc/posix-functions/wcsnlen.texi
@@ -4,19 +4,19 @@
 
 POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/wcsnlen.html}
 
-Gnulib module: ---
+Gnulib module: wcsnlen
 
 Portability problems fixed by Gnulib:
 @itemize
+@item
+This function is missing on some platforms:
+MacOS X 10.5, FreeBSD 6.0, NetBSD 5.0, OpenBSD 3.8, AIX 4.3.2, HP-UX 11,
+IRIX 6.5, OSF/1 5.1, Solaris 10, Cygwin 1.5.x, mingw, Interix 3.5, BeOS.
 @end itemize
 
 Portability problems not fixed by Gnulib:
 @itemize
 @item
-This function is missing on some platforms:
-MacOS X 10.5, FreeBSD 6.0, NetBSD 5.0, OpenBSD 3.8, AIX 4.3.2, HP-UX
-11, IRIX 6.5, OSF/1 5.1, Solaris 10, Cygwin 1.5.x, mingw, Interix 3.5, BeOS.
-@item
 On AIX and Windows platforms, @code{wchar_t} is a 16-bit type and therefore cannot
 accommodate all Unicode characters.
 @end itemize

--- a/lib/wchar.in.h
+++ b/lib/wchar.in.h
@@ -533,6 +533,22 @@
 #endif
 
 
+/* Return the number of wide characters in S, but at most MAXLEN.  */
+#if @GNULIB_WCSNLEN@
+# if !@HAVE_WCSNLEN@
+_GL_FUNCDECL_SYS (wcsnlen, size_t, (const wchar_t *s, size_t maxlen));
+# endif
+_GL_CXXALIAS_SYS (wcsnlen, size_t, (const wchar_t *s, size_t maxlen));
+_GL_CXXALIASWARN (wcsnlen);
+#elif defined GNULIB_POSIXCHECK
+# undef wcsnlen
+# if HAVE_RAW_DECL_WCSNLEN
+_GL_WARN_ON_USE (wcsnlen, "wcsnlen is unportable - "
+                 "use gnulib module wcsnlen for portability");
+# endif
+#endif
+
+
 #endif /* _GL_WCHAR_H */
 #endif /* _GL_WCHAR_H */
 #endif

new file mode 100644
--- /dev/null
+++ b/lib/wcsnlen-impl.h
@@ -0,0 +1,26 @@
+/* Determine the length of a size-bounded wide string.
+   Copyright (C) 1999, 2011 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 1999.
+
+   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/>.  */
+
+size_t
+wcsnlen (const wchar_t *s, size_t maxlen)
+{
+  const wchar_t *ptr;
+
+  for (ptr = s; maxlen > 0 && *ptr != (wchar_t)'\0'; ptr++, maxlen--)
+    ;
+  return ptr - s;
+}

new file mode 100644
--- /dev/null
+++ b/lib/wcsnlen.c
@@ -0,0 +1,23 @@
+/* Determine the length of a size-bounded wide string.
+   Copyright (C) 2011 Free Software Foundation, Inc.
+   Written by Bruno Haible <bruno@clisp.org>, 2011.
+
+   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/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <wchar.h>
+
+#include "wcsnlen-impl.h"

--- a/m4/wchar_h.m4
+++ b/m4/wchar_h.m4
@@ -51,7 +51,7 @@
     ]],
     [btowc wctob mbsinit mbrtowc mbrlen mbsrtowcs mbsnrtowcs wcrtomb
      wcsrtombs wcsnrtombs wcwidth wmemchr wmemcmp wmemcpy wmemmove wmemset
-     wcslen
+     wcslen wcsnlen
     ])
 ])
 
@@ -152,6 +152,7 @@
   GNULIB_WMEMMOVE=0;   AC_SUBST([GNULIB_WMEMMOVE])
   GNULIB_WMEMSET=0;    AC_SUBST([GNULIB_WMEMSET])
   GNULIB_WCSLEN=0;     AC_SUBST([GNULIB_WCSLEN])
+  GNULIB_WCSNLEN=0;    AC_SUBST([GNULIB_WCSNLEN])
   dnl Assume proper GNU behavior unless another module says otherwise.
   HAVE_BTOWC=1;         AC_SUBST([HAVE_BTOWC])
   HAVE_MBSINIT=1;       AC_SUBST([HAVE_MBSINIT])
@@ -168,6 +169,7 @@
   HAVE_WMEMMOVE=1;      AC_SUBST([HAVE_WMEMMOVE])
   HAVE_WMEMSET=1;       AC_SUBST([HAVE_WMEMSET])
   HAVE_WCSLEN=1;        AC_SUBST([HAVE_WCSLEN])
+  HAVE_WCSNLEN=1;       AC_SUBST([HAVE_WCSNLEN])
   HAVE_DECL_WCTOB=1;    AC_SUBST([HAVE_DECL_WCTOB])
   HAVE_DECL_WCWIDTH=1;  AC_SUBST([HAVE_DECL_WCWIDTH])
   REPLACE_MBSTATE_T=0;  AC_SUBST([REPLACE_MBSTATE_T])

new file mode 100644
--- /dev/null
+++ b/m4/wcsnlen.m4
@@ -0,0 +1,15 @@
+# wcsnlen.m4 serial 1
+dnl Copyright (C) 2011 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_FUNC_WCSNLEN],
+[
+  AC_REQUIRE([gl_WCHAR_H_DEFAULTS])
+  AC_CHECK_FUNCS_ONCE([wcsnlen])
+  if test $ac_cv_func_wcsnlen = no; then
+    HAVE_WCSNLEN=0
+    AC_LIBOBJ([wcsnlen])
+  fi
+])

--- a/modules/wchar
+++ b/modules/wchar
@@ -47,6 +47,7 @@
 	      -e 's|@''GNULIB_WMEMMOVE''@|$(GNULIB_WMEMMOVE)|g' \
 	      -e 's|@''GNULIB_WMEMSET''@|$(GNULIB_WMEMSET)|g' \
 	      -e 's|@''GNULIB_WCSLEN''@|$(GNULIB_WCSLEN)|g' \
+	      -e 's|@''GNULIB_WCSNLEN''@|$(GNULIB_WCSNLEN)|g' \
 	      -e 's|@''HAVE_WINT_T''@|$(HAVE_WINT_T)|g' \
 	      -e 's|@''HAVE_BTOWC''@|$(HAVE_BTOWC)|g' \
 	      -e 's|@''HAVE_MBSINIT''@|$(HAVE_MBSINIT)|g' \
@@ -63,6 +64,7 @@
 	      -e 's|@''HAVE_WMEMMOVE''@|$(HAVE_WMEMMOVE)|g' \
 	      -e 's|@''HAVE_WMEMSET''@|$(HAVE_WMEMSET)|g' \
 	      -e 's|@''HAVE_WCSLEN''@|$(HAVE_WCSLEN)|g' \
+	      -e 's|@''HAVE_WCSNLEN''@|$(HAVE_WCSNLEN)|g' \
 	      -e 's|@''HAVE_DECL_WCTOB''@|$(HAVE_DECL_WCTOB)|g' \
 	      -e 's|@''HAVE_DECL_WCWIDTH''@|$(HAVE_DECL_WCWIDTH)|g' \
 	      -e 's|@''REPLACE_MBSTATE_T''@|$(REPLACE_MBSTATE_T)|g' \

new file mode 100644
--- /dev/null
+++ b/modules/wcsnlen
@@ -0,0 +1,25 @@
+Description:
+wcsnlen() function: determine the length of a size-bounded wide string.
+
+Files:
+lib/wcsnlen.c
+lib/wcsnlen-impl.h
+m4/wcsnlen.m4
+
+Depends-on:
+wchar
+
+configure.ac:
+gl_FUNC_WCSNLEN
+gl_WCHAR_MODULE_INDICATOR([wcsnlen])
+
+Makefile.am:
+
+Include:
+<wchar.h>
+
+License:
+LGPL
+
+Maintainer:
+Bruno Haible

--- a/tests/test-wchar-c++.cc
+++ b/tests/test-wchar-c++.cc
@@ -104,6 +104,10 @@
 SIGNATURE_CHECK (GNULIB_NAMESPACE::wcslen, size_t, (const wchar_t *));
 #endif
 
+#if GNULIB_TEST_WCSNLEN
+SIGNATURE_CHECK (GNULIB_NAMESPACE::wcsnlen, size_t, (const wchar_t *, size_t));
+#endif
+
 
 int
 main ()