Date: Sat, 5 Jul 1997 23:30:01 -0700 (PDT) From: ac199@hwcn.org To: freebsd-bugs Subject: Re: bin/3451 : vasprintf() doesn't work. Message-ID: <199707060630.XAA10113@hub.freebsd.org>
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The following reply was made to PR bin/3451; it has been noted by GNATS.
From: ac199@hwcn.org
To: freebsd-gnats-submit@freebsd.org, tim@X2296
Cc: Subject: Re: bin/3451 : vasprintf() doesn't work.
Date: Sun, 6 Jul 1997 02:26:47 -0400 (EDT)
>
> How-To-Repeat
As a demonstration of my dedication and intelligence :), this pr now
includes, in addition to the ~5 line good fix and detailed explanation of
it, demonstration code!
Read the Caveat, though... Tested on 2.2.2 (the bug exists in -current,
as of July 5, but I've not tested this code there).
/*
* CAVEAT: This code depends on a specific behaviour of malloc(3).
* If, at some point in the future, it stops demonstrating the
* vasprintf(3) bug, it could be because the behaviour of malloc()
* has been changed subtly, instead of being because vasprintf()
* has been fixed.
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
char d[] = "In an effort to keep this demonstration as simple and
to the point as possible, I use this string instead of mallocing and
memsetting. This string will be cut to exactly 128 characters.";
main() {
static char * a, * b, * c; /* static makes debugging w/
* watches easier */
d[128] = '\0'; /* cut d to proper size */
a = malloc (128); /* 128 == CHUNK_SPARE in vasprintf.c */
b = malloc (70); /* This is very tricky. If we alloc too little
* (or too much) space here, malloc() will send
* the next malloc(128) off into the boonies,
* even though we free(a) 128. */
free (a); /* asprintf will malloc(128) and get what I just
* free()'d. The memory at b should be contigious. */
strcpy (b, "string");
asprintf (&c, d);
printf ("b %s equals \"string\". It is \"%s\".\n",
strcmp(b,"string") ? "no longer" : "still", b);
/* At no point have we touched b since strcpy(). It should still
* say "string", but it won't... */
}
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