malloc(0)

[Zack Weinberg]

There's been some discussion recently in comp.std.c about what
malloc(0) and realloc(x, 0) are supposed to do.  The standard allows
returning some non-null pointer in both cases, which is what we
currently do.  However, that non-null pointer has peculiar
characteristics and it seems to me that it would be less surprising if
both these operations returned NULL.

Proposed patch follows.  Comment?

zw

Mon Jun  1 09:54:24 1998  Zack Weinberg  <zack@rabi.phys.columbia.edu>

	* malloc/malloc.c: Define REALLOC_ZERO_BYTES_FREES.
	(mALLOc): Return 0 if R_Z_B_F is defined and bytes == 0.

============================================================
Index: malloc/malloc.c
--- malloc/malloc.c	Sat, 30 May 1998 16:12:00 -0400 zack  Z.7
+++ malloc/malloc.c	Mon, 01 Jun 1998 09:51:44 -0400 zack  Z.7(w)
@@ -373,7 +373,7 @@
 */
 
 
-/*   #define REALLOC_ZERO_BYTES_FREES */
+#define REALLOC_ZERO_BYTES_FREES
 
 
 /*
@@ -2586,6 +2586,13 @@
   }
 #endif
 
+#ifdef REALLOC_ZERO_BYTES_FREES
+  /* zw: for consistency, in this case make malloc(0) do nothing
+     and return NULL. */
+  if (bytes == 0)
+    return 0;
+#endif
+  
   nb = request2size(bytes);
   arena_get(ar_ptr, nb);
   if(!ar_ptr)