Add arena_free()

include/arena.h

@@ -17,5 +17,6 @@ void* arena_alloc(arena_t* a, size_t len);
 void* arena_calloc(arena_t* a, size_t nmemb, size_t size);
 void* arena_realloc_tail(arena_t* a, size_t len);
 void arena_delete(arena_t* a);
+void arena_free(arena_t* a, void* p);
 
 #endif

src/arena.c

@@ -83,3 +83,11 @@ void arena_delete(arena_t* a)
     arena_reset(a);
     a->data = NULL;
 }
+
+// included for completeness
+void arena_free(arena_t* a, void* p)
+{
+    (void)p;
+    (void)a;
+    return;
+}