WUtil: New macro 'wlengthof' in the public API to get number of elements in an array

The new macro 'wlengthof' returns the number of elements for which a local
array have been defined, which makes code easier to read than the
previous [sizeof() / sizeof([0]) ] construct.

The macro includes a static assertion to stop compilation if it is being
used on a pointer, for which we cannot know the size of the array, to
avoid generating dummy result. This can work only with C11 which
standardised the static assertions.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

WINGs/WINGs/WUtil.h

@@ -88,6 +88,27 @@
 #endif /* !NDEBUG */
 
 
+#ifdef static_assert
+# define _wutil_static_assert(check, message) static_assert(check, message)
+#else
+# ifdef __STDC_VERSION__
+#  if __STDC_VERSION__ >= 201112L
+/*
+ * Ideally, we would like to include <assert.h> to have 'static_assert'
+ * properly defined, but as we have to be sure about portability and
+ * because we're a public header we can't count on 'configure' to tell
+ * us about availability, so we use the raw C11 keyword
+ */
+#   define _wutil_static_assert(check, message) _Static_assert(check, message)
+#  else
+#   define _wutil_static_assert(check, message) /**/
+#  endif
+# else
+#  define _wutil_static_assert(check, message) /**/
+# endif
+#endif
+
+
 #ifdef __cplusplus
 extern "C" {
 #endif /* __cplusplus */
@@ -182,6 +203,16 @@ typedef void WMNotificationObserverAction(void *observerData,
                                           WMNotification *notification);
 
 
+/* ---[ Macros ]---------------------------------------------------------- */
+
+#define wlengthof(array)  \
+	({   \
+		_wutil_static_assert(sizeof(array) > sizeof(array[0]),   \
+		                     "the macro 'wlengthof' cannot be used on pointers, only on known size arrays");   \
+		sizeof(array) / sizeof(array[0]);   \
+	})
+
+
 /* ---[ WINGs/memory.c ]-------------------------------------------------- */
 
 void* wmalloc(size_t size);

configure.ac

@@ -54,7 +54,7 @@ WINGS_VERSION=$WINGS_CURRENT:$WINGS_REVISION:$WINGS_AGE
 AC_SUBST(WINGS_VERSION)
 dnl
 dnl libWUtil
-WUTIL_CURRENT=3
+WUTIL_CURRENT=4
 WUTIL_REVISION=0
 WUTIL_AGE=0
 WUTIL_VERSION=$WUTIL_CURRENT:$WUTIL_REVISION:$WUTIL_AGE