vlc_strerror() and vlc_strerror_c() convenience wrappers

Those are more flexible than the GNU-specific %m format specifier to
print standard error messages. They are also less likely to format a
clobbered error number.

include/vlc_messages.h

@@ -81,6 +81,9 @@ VLC_API void vlc_vaLog(vlc_object_t *, int,
 # define MODULE_STRING __FILE__
 #endif
 
+VLC_API const char *vlc_strerror(int);
+VLC_API const char *vlc_strerror_c(int);
+
 /**
  * @}
  */

src/Makefile.am

@@ -270,6 +270,7 @@ SOURCES_libvlc_android = \
 
 SOURCES_libvlc_linux = \
 	posix/dirs.c \
+	posix/error.c \
 	posix/filesystem.c \
 	posix/netconf.c \
 	posix/plugin.c \
@@ -312,6 +313,7 @@ SOURCES_libvlc_os2 = \
 
 SOURCES_libvlc_other = \
 	posix/dirs.c \
+	posix/error.c \
 	posix/filesystem.c \
 	posix/netconf.c \
 	posix/thread.c \

src/libvlccore.sym

@@ -255,6 +255,8 @@ vlc_module_unload
 vlc_Log
 vlc_LogSet
 vlc_vaLog
+vlc_strerror
+vlc_strerror_c
 msleep
 mstrtime
 mwait

src/posix/error.c

+/*****************************************************************************
+ * error.c: POSIX error messages formatting
+ *****************************************************************************
+ * Copyright © 2013 Rémi Denis-Courmont
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston MA 02110-1301, USA.
+ *****************************************************************************/
+
+#ifdef HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <string.h>
+#include <locale.h>
+
+#include <vlc_common.h>
+
+static const char *vlc_strerror_l(int errnum, const char *lname)
+{
+    locale_t loc = newlocale(LC_MESSAGES_MASK, lname, (locale_t)0);
+    const char *buf = strerror_l(errnum, loc);
+
+    freelocale(loc);
+    return buf;
+}
+
+/**
+ * Formats an error message in the current locale.
+ * @param errnum error number (as in errno.h)
+ * @return A string pointer, valid until the next call to a function of the
+ * strerror() family in the same thread. This function cannot fail.
+ */
+const char *vlc_strerror(int errnum)
+{
+    /* We cannot simply use strerror() here, since it is not thread-safe. */
+    return vlc_strerror_l(errnum, "");
+}
+
+/**
+ * Formats an error message in the POSIX/C locale (i.e. American English).
+ * @param errnum error number (as in errno.h)
+ * @return A string pointer, valid until the next call to a function of the
+ * strerror() family in the same thread. This function cannot fail.
+ */
+const char *vlc_strerror_c(int errnum)
+{
+    return vlc_strerror_l(errnum, "C");
+}