From fb5f7ad971ea9b7cc92cc43c03973c318b716f6d Mon Sep 17 00:00:00 2001
From: Jef Driesen <jefdriesen@users.sourceforge.net>
Date: Wed, 4 Nov 2015 19:42:17 +0100
Subject: [PATCH] Use the GCC printf format attribute.

This enables the compiler to check the arguments against a printf style
format string in all calls to the logging functions.
---
 examples/utils.h      | 8 +++++++-
 src/context-private.h | 8 +++++++-
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/examples/utils.h b/examples/utils.h
index e43c06c..7562beb 100644
--- a/examples/utils.h
+++ b/examples/utils.h
@@ -26,9 +26,15 @@
 extern "C" {
 #endif /* __cplusplus */
 
+#if defined(__GNUC__)
+#define ATTR_FORMAT_PRINTF(a,b) __attribute__((format(printf, a, b)))
+#else
+#define ATTR_FORMAT_PRINTF(a,b)
+#endif
+
 #define WARNING(expr) message ("%s:%d: %s\n", __FILE__, __LINE__, expr)
 
-int message (const char* fmt, ...);
+int message (const char* fmt, ...) ATTR_FORMAT_PRINTF(1, 2);
 
 void message_set_logfile (const char* filename);
 
diff --git a/src/context-private.h b/src/context-private.h
index e7509bf..7f50a68 100644
--- a/src/context-private.h
+++ b/src/context-private.h
@@ -40,6 +40,12 @@ extern "C" {
 #define FUNCTION __FUNCTION__
 #endif
 
+#if defined(__GNUC__)
+#define ATTR_FORMAT_PRINTF(a,b) __attribute__((format(printf, a, b)))
+#else
+#define ATTR_FORMAT_PRINTF(a,b)
+#endif
+
 #ifdef ENABLE_LOGGING
 #define HEXDUMP(context, loglevel, prefix, data, size) dc_context_hexdump (context, loglevel, __FILE__, __LINE__, FUNCTION, prefix, data, size)
 #define SYSERROR(context, errcode) dc_context_syserror (context, DC_LOGLEVEL_ERROR, __FILE__, __LINE__, FUNCTION, errcode)
@@ -57,7 +63,7 @@ extern "C" {
 #endif
 
 dc_status_t
-dc_context_log (dc_context_t *context, dc_loglevel_t loglevel, const char *file, unsigned int line, const char *function, const char *format, ...);
+dc_context_log (dc_context_t *context, dc_loglevel_t loglevel, const char *file, unsigned int line, const char *function, const char *format, ...) ATTR_FORMAT_PRINTF(6, 7);
 
 dc_status_t
 dc_context_syserror (dc_context_t *context, dc_loglevel_t loglevel, const char *file, unsigned int line, const char *function, int errcode);