Listing 2 strncmp.c — similar to memcmp, except that it also stops on a terminating null character and can use its pointer arguments directly.

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

int (strncmp)(const char *s1, const char *s2, size_t n)
    {   /* compare unsigned char s1[max n], s2[max n] */
    for (; 0 < n; ++s1, ++s2, --n)
       if (*s1 != *s2)
          return ((*(unsigned char *)s1
              < *(unsigned char *)s2) ? -1 : +1);
       else if (*s1 == '\0')
          return (0);
    return (0);
    }
/* End of File */