--- a/ChangeLog	Sun Apr 30 12:15:08 2017 +0200
+++ b/ChangeLog	Sun Apr 30 13:19:24 2017 +0200
@@ -1,3 +1,15 @@
+2017-04-30  Bruno Haible  <bruno@clisp.org>
+
+	ctime: New module.
+	* lib/time.in.h (ctime): New declaration.
+	* lib/ctime.c: New file.
+	* m4/ctime.m4: New file.
+	* m4/time_h.m4 (gl_HEADER_TIME_H_DEFAULTS): Initialize GNULIB_CTIME,
+	REPLACE_CTIME.
+	* modules/time (Makefile.am): Substitute GNULIB_CTIME, REPLACE_CTIME.
+	* modules/ctime: New file.
+	* doc/posix-functions/ctime.texi: Mention the new module.
+
 2017-04-30  Bruno Haible  <bruno@clisp.org>
 
 	gettimeofday: Provide higher resolution on native Windows.

--- a/doc/posix-functions/ctime.texi	Sun Apr 30 12:15:08 2017 +0200
+++ b/doc/posix-functions/ctime.texi	Sun Apr 30 13:19:24 2017 +0200
@@ -4,18 +4,18 @@
 
 POSIX specification:@* @url{http://www.opengroup.org/onlinepubs/9699919799/functions/ctime.html}
 
-Gnulib module: ---
+Gnulib module: ctime
 
 Portability problems fixed by Gnulib:
 @itemize
+@item
+On native Windows platforms (mingw, MSVC), this function works incorrectly
+when the environment variable @code{TZ} has been set by Cygwin.
 @end itemize
 
 Portability problems not fixed by Gnulib:
 @itemize
 @item
-On native Windows platforms (mingw, MSVC), this function works incorrectly
-when the environment variable @code{TZ} has been set by Cygwin.
-@item
 This function may overflow its internal buffer if an invalid year is passed.
 @item
 The @code{ctime} function need not be reentrant, and consequently is

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/lib/ctime.c	Sun Apr 30 13:19:24 2017 +0200
@@ -0,0 +1,40 @@
+/* Work around platform bugs in ctime.
+   Copyright (C) 2017 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/>.  */
+
+#include <config.h>
+
+/* Specification.  */
+#include <time.h>
+
+#include <stdlib.h>
+#include <string.h>
+
+#undef ctime
+
+char *
+rpl_ctime (const time_t *tp)
+{
+#if (defined _WIN32 || defined __WIN32__) && ! defined __CYGWIN__
+  /* If the environment variable TZ has been set by Cygwin, neutralize it.
+     The Microsoft CRT interprets TZ differently than Cygwin and produces
+     incorrect results if TZ has the syntax used by Cygwin.  */
+  const char *tz = getenv ("TZ");
+  if (tz != NULL && strchr (tz, '/') != NULL)
+    _putenv ("TZ=");
+#endif
+
+  return ctime (tp);
+}

--- a/lib/time.in.h	Sun Apr 30 12:15:08 2017 +0200
+++ b/lib/time.in.h	Sun Apr 30 13:19:24 2017 +0200
@@ -233,6 +233,22 @@
 _GL_CXXALIASWARN (strptime);
 # endif
 
+/* Convert *TP to a date and time string.  See
+   <http://pubs.opengroup.org/onlinepubs/9699919799/functions/ctime.html>.  */
+# if @GNULIB_CTIME@
+#  if @REPLACE_CTIME@
+#   if !(defined __cplusplus && defined GNULIB_NAMESPACE)
+#    define ctime rpl_ctime
+#   endif
+_GL_FUNCDECL_RPL (ctime, char *, (time_t const *__tp)
+                                 _GL_ARG_NONNULL ((1)));
+_GL_CXXALIAS_RPL (ctime, char *, (time_t const *__tp));
+#  else
+_GL_CXXALIAS_SYS (ctime, char *, (time_t const *__tp));
+#  endif
+_GL_CXXALIASWARN (ctime);
+# endif
+
 # if defined _GNU_SOURCE && @GNULIB_TIME_RZ@ && ! @HAVE_TIMEZONE_T@
 typedef struct tm_zone *timezone_t;
 _GL_FUNCDECL_SYS (tzalloc, timezone_t, (char const *__name));

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/m4/ctime.m4	Sun Apr 30 13:19:24 2017 +0200
@@ -0,0 +1,15 @@
+# ctime.m4 serial 1
+dnl Copyright (C) 2017 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_CTIME],
+[
+  AC_REQUIRE([gl_HEADER_TIME_H_DEFAULTS])
+  AC_REQUIRE([AC_CANONICAL_HOST])
+  case "$host_os" in
+    mingw*) REPLACE_CTIME=1 ;;
+    *)      REPLACE_CTIME=0 ;;
+  esac
+])

--- a/m4/time_h.m4	Sun Apr 30 12:15:08 2017 +0200
+++ b/m4/time_h.m4	Sun Apr 30 13:19:24 2017 +0200
@@ -2,7 +2,7 @@
 
 # Copyright (C) 2000-2001, 2003-2007, 2009-2017 Free Software Foundation, Inc.
 
-# serial 9
+# serial 10
 
 # This file is free software; the Free Software Foundation
 # gives unlimited permission to copy and/or distribute it,
@@ -104,6 +104,7 @@
 
 AC_DEFUN([gl_HEADER_TIME_H_DEFAULTS],
 [
+  GNULIB_CTIME=0;                        AC_SUBST([GNULIB_CTIME])
   GNULIB_MKTIME=0;                       AC_SUBST([GNULIB_MKTIME])
   GNULIB_NANOSLEEP=0;                    AC_SUBST([GNULIB_NANOSLEEP])
   GNULIB_STRPTIME=0;                     AC_SUBST([GNULIB_STRPTIME])
@@ -118,6 +119,7 @@
   dnl If another module says to replace or to not replace, do that.
   dnl Otherwise, replace only if someone compiles with -DGNULIB_PORTCHECK;
   dnl this lets maintainers check for portability.
+  REPLACE_CTIME=GNULIB_PORTCHECK;        AC_SUBST([REPLACE_CTIME])
   REPLACE_LOCALTIME_R=GNULIB_PORTCHECK;  AC_SUBST([REPLACE_LOCALTIME_R])
   REPLACE_MKTIME=GNULIB_PORTCHECK;       AC_SUBST([REPLACE_MKTIME])
   REPLACE_NANOSLEEP=GNULIB_PORTCHECK;    AC_SUBST([REPLACE_NANOSLEEP])

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/modules/ctime	Sun Apr 30 13:19:24 2017 +0200
@@ -0,0 +1,27 @@
+Description:
+ctime() function: convert time to string.
+
+Files:
+lib/ctime.c
+m4/ctime.m4
+
+Depends-on:
+time
+
+configure.ac:
+gl_FUNC_CTIME
+if test $REPLACE_CTIME = 1; then
+  AC_LIBOBJ([ctime])
+fi
+gl_TIME_MODULE_INDICATOR([ctime])
+
+Makefile.am:
+
+Include:
+<time.h>
+
+License:
+LGPLv2+
+
+Maintainer:
+all

--- a/modules/time	Sun Apr 30 12:15:08 2017 +0200
+++ b/modules/time	Sun Apr 30 13:19:24 2017 +0200
@@ -30,6 +30,7 @@
 	      -e 's|@''PRAGMA_SYSTEM_HEADER''@|@PRAGMA_SYSTEM_HEADER@|g' \
 	      -e 's|@''PRAGMA_COLUMNS''@|@PRAGMA_COLUMNS@|g' \
 	      -e 's|@''NEXT_TIME_H''@|$(NEXT_TIME_H)|g' \
+	      -e 's/@''GNULIB_CTIME''@/$(GNULIB_CTIME)/g' \
 	      -e 's/@''GNULIB_GETTIMEOFDAY''@/$(GNULIB_GETTIMEOFDAY)/g' \
 	      -e 's/@''GNULIB_MKTIME''@/$(GNULIB_MKTIME)/g' \
 	      -e 's/@''GNULIB_NANOSLEEP''@/$(GNULIB_NANOSLEEP)/g' \
@@ -42,6 +43,7 @@
 	      -e 's|@''HAVE_STRPTIME''@|$(HAVE_STRPTIME)|g' \
 	      -e 's|@''HAVE_TIMEGM''@|$(HAVE_TIMEGM)|g' \
 	      -e 's|@''HAVE_TIMEZONE_T''@|$(HAVE_TIMEZONE_T)|g' \
+	      -e 's|@''REPLACE_CTIME''@|$(REPLACE_CTIME)|g' \
 	      -e 's|@''REPLACE_GMTIME''@|$(REPLACE_GMTIME)|g' \
 	      -e 's|@''REPLACE_LOCALTIME''@|$(REPLACE_LOCALTIME)|g' \
 	      -e 's|@''REPLACE_LOCALTIME_R''@|$(REPLACE_LOCALTIME_R)|g' \