New subject: strcmp() segfaults if one (and only one) of the parameters is NULL ?

5 Jul 2011


      Hi,
strcmp() returns 0 if both are parameters NULL, but segfaults if one
of the parameters is NULL.
Is this a known behaviour ? man page says nothing about NULL parameters.
I ask because,  vdr checks for NULL parameter(s) to strcmp() sometimes.
Check for one or both parameters:
epg.c:692:  if (shortText && strcmp(title, shortText) == 0) {
epg.c:742:  if (shortText && description && strcmp(shortText,
description) == 0) {
No check for null parameter:
channels.c:227:     bool nn = strcmp(name, Name) != 0;
channels.c:228:     bool ns = strcmp(shortName, ShortName) != 0;
-- 
Thanks,
Sundararaj


$ /lib/libc.so.6
GNU C Library (Ubuntu EGLIBC 2.11.1-0ubuntu7.7) stable release version
2.11.1, by Roland McGrath et al.
...
Compiled by GNU CC version 4.4.3.
Compiled on a Linux >>2.6.24-28-server<< system on 2011-01-11.
Available extensions:
    crypt add-on version 2.1 by Michael Glad and others
    GNU Libidn by Simon Josefsson
    Native POSIX Threads Library by Ulrich Drepper et al
    BIND-8.2.3-T5B


/*---------------------------------------------------------------*/

#include <string.h>
#include <stdio.h>

int main()
{
    int nn;

    printf("trying strcmp(NULL,NULL)\n");
    nn = strcmp(NULL, NULL); /* no segfault */

    printf("trying strcmp("non null string",NULL)\n");
    nn = strcmp("non null string", NULL);  /* segfault */

    printf("does not reach here\n");

    return 0;
} /* main() */

/*-------------------------------------------------------------------*/


in gdb I get this backtrace
#0  __strcmp_ia32 () at ../sysdeps/i386/i686/multiarch/../strcmp.S:40