Listing 1 memcmp.c — performs unsigned char comparisons to meet the requirements of the C Standard.

/* memcmp function */
#include <string.h>

int (memcmp)(const void *s1, const void *s2, size_t n)
    {   /* compare unsigned char s1[n], s2[n] */
    const unsigned char *su1 = (const unsigned char *)s1;
    const unsigned char *su2 = (const unsigned char *)s2;

    for (; 0 < n; ++su1, ++su2, --n)
       if (*su1 != *su2)
          return ((*su1 < *su2) ? -1 : +1);
    return (0);
    }
/* End of File */