This documentation is copyright © 1998-2001 Sandro Sigala <sandro@sigala.it>.
All rights reserved.

Released under the GNU General Public License.

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memcmp

Prototype

#include <string.h>

int memcmp(const void *s1, const void *s2, size_t n);

Description

Compares the first n bytes of the two memory areas s1 and s2. It returns an integer less than, equal to, or greater than zero if s1 is found, respectively, to be less than, to match, or be greater than s2.

Implementation

View source
#include <string.h>

int memcmp(const void *s1, const void *s2, size_t n)
{
    const unsigned char *sp1, *sp2;

    for (sp1 = s1, sp2 = s2; n > 0; ++sp1, ++sp2, --n)
	if (*sp1 != *sp2)
	    return (*sp1 < *sp2) ? -1 : 1;

    return 0;
}

Example

View source
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

/*
 * Check if two objects are equal (contain the same data).
 */
#define OBJEQ(obj1, obj2)			\
	(sizeof(obj1) == sizeof(obj2) &&	\
	 memcmp(&(obj1), &(obj2), sizeof(obj1)) == 0)

int main(void)
{
    int a = 1, b = 1, c = 2;
    int *bp = &b;
    char d = 1;

    printf("%d\n", OBJEQ(a, b));   /* Prints "1". */
    printf("%d\n", OBJEQ(a, c));   /* Prints "0". */
    printf("%d\n", OBJEQ(a, *bp)); /* Prints "1". */
    printf("%d\n", OBJEQ(a, d));   /* Prints "0". */

    return EXIT_SUCCESS;
}

References

ISO C 9899:1990 7.11.4.1