Introduce warn_unused_result macro

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@73982 15284696-431f-4ddb-bdfa-cd5b030d7da7

include/defs/imagery.h

@@ -164,7 +164,7 @@ int I_InitSigSet(struct SigSet *);
 int I_SigSetNBands(struct SigSet *, int);
 struct ClassSig *I_NewClassSig(struct SigSet *);
 struct SubSig *I_NewSubSig(struct SigSet *, struct ClassSig *);
-int I_ReadSigSet(FILE *, struct SigSet *);
+int I_ReadSigSet(FILE *, struct SigSet *) WARN_UNUSED_RESULT;
 int I_SetSigTitle(struct SigSet *, const char *);
 const char *I_GetSigTitle(const struct SigSet *);
 int I_SetClassTitle(struct ClassSig *, const char *);

include/gis.h

@@ -67,6 +67,13 @@ static const char *GRASS_copyright __attribute__ ((unused))
 #  define HOST_NEWLINE "\n"
 #endif
 
+/*! \brief Generate warning if function return value is unused */
+#if __GNUC_PREREQ (3,4)
+    #define WARN_UNUSED_RESULT __attribute__ ((warn_unused_result))
+#else
+    #define WARN_UNUSED_RESULT
+#endif
+
 /*!
   \brief List of units
 */