NetNews Usenet Archive 1992 #27/NN_1992_27.iso/spool/comp/std/c/3055

Text File | 1992-11-22 | 1.6 KB | 51 lines

Path: sparky!uunet!mcsun!sun4nl!and!jos
From: [e-mail] (Jos Horsmeier)
Newsgroups: comp.std.c
Subject: Re: malloc(0)
Message-ID: <[e-mail]>
Date: 23 Nov 92 10:41:27 GMT
References: <[e-mail]> <[e-mail]> <[e-mail]>
Organization: AND Software BV Rotterdam
Lines: 40

In article <[e-mail]> [e-mail] (Larry Jones) writes:
|In article <[e-mail]>, [e-mail] (Jerry Schwarz) writes:
|< The standard says  (refering to allocation routines)
|<
|<     If the size of the space requested is zero, the behavior
|<     is implementation-defined; the value returned shall be
|<     either a null pointer or a unique pointer.
|<
|< I have always read "unique pointer" as meaning different from
|< previously allocated pointers including pointers previously
|< returned by malloc(0).
|
|That was indeed the committee's intent.  If every call for zero space
|returned the same pointer it wouldn't be very unique, would it?

No it wouldn't, but if it would return a unique pointer value,it would
brake code like this:

char *p= malloc(0);
char *q= malloc(0);

if (p == q)
    printf("malloc returned NULL or non-unique value"\n");
else
    printf("malloc returned two unique pointers\n");

when ported from a system where malloc(0) returns NULL to a system
where malloc would return a unique pointer every time it was
called with a size of zero ...

regards,

Jos aka [e-mail]

ps. Bill Mitchell ([e-mail]) quoted the rationale
    concerning this topic <[e-mail]>
    but the rationale doesn't say much about this (pathetic) little
    problem ...