linux-kernel - Re: [PATCH] Repalce strncmp by memcmp

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Date:	Mon, 29 Nov 2010 06:11:21 +0300
From:	Pavel Vasilyev <pavel@...linux.ru>
To:	Ming Lei <tom.leiming@...il.com>
CC:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Repalce strncmp by memcmp

On 29.11.2010 05:29, Ming Lei wrote:
> Hi,
>
> 2010/11/29 Pavel Vasilyev <pavel@...linux.ru>:
>>    This patch replace all strncmp(a, b, c) by  memcmp(a, b, c).
>>
>> I test on x86_64 (AMD Opteron 285).
> In fact, memcmp doesn't handle case of tail of string, so
> it is not safe to replace strncmp with memcmp
>
#include <stdio.h>
#include <errno.h>

int main() {

   char *STR = "XXXX\0";
   char *XXX = "XXXX";
   int a, b;

     errno = 0; a = memcmp(STR, XXX, 5);  a += errno;
     errno = 0; b = strncmp(STR, XXX, 5); b += errno;
     printf("5 chars: %d %d \n", a, b);
     errno = 0; a = memcmp(STR, XXX, 4);  a += errno;
     errno = 0; b = strncmp(STR, XXX, 4); b += errno;
     printf("4 chars: %d %d \n", a, b);

     printf("SWAP STRINGS\n");

     errno = 0; a = memcmp(XXX, STR, 5);  a += errno;
     errno = 0; b = strncmp(XXX, STR, 5); b += errno;
     printf("5 chars: %d %d \n", a, b);
     errno = 0; a = memcmp(XXX, STR, 4);  a += errno;
     errno = 0; b = strncmp(XXX, STR, 4); b += errno;
     printf("4 chars: %d %d \n", a, b);

return 0;
}
----
# ./a.out
5 chars: 0 0
4 chars: 0 0
SWAP STRINGS
5 chars: 0 0
4 chars: 0 0

But I think the same thing  ;)

-- 

                                                         Pavel.

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