C-Allocators: Mention cleanup attribute

Signed-off-by: Daiki Ueno <dueno@redhat.com>

modules/ROOT/pages/programming-languages/C-Allocators.adoc

@@ -105,6 +105,30 @@ Otherwise, call `malloc`. When exiting the
 function, check if `malloc` had been called,
 and free the buffer as needed.
 
+If portability is not important in your program, an alternative way of
+automatic memory management is to leverage the `cleanup` attribute
+supported by the recent versions of GCC and Clang. If a local variable
+is declared with the attribute, the specified cleanup function will be
+called when the variable goes out of scope.
+
+[source,c]
+----
+static inline void freep(void *p) {
+        free(*(void**) p);
+}
+
+void somefunction(const char *param) {
+	if (strcmp(param, "do_something_complex") == 0) {
+		__attribute__((cleanup(freep))) char *ptr = NULL;
+
+		/* Allocate a temporary buffer */
+		ptr = malloc(size);
+
+		/* Do something on it, but do not need to manually call free() */
+	}
+}
+----
+
 [[sect-Defensive_Coding-C-Allocators-Arrays]]
 === Array Allocation