C String Functions - C memcmp

Compares memory locations.

int memcmp(const void *str1 , const void *str2 , size_t n );

Compares the first n bytes of str1 and str2.

Does not stop comparing even after the null character.

Returns zero if the first n bytes of str1 and str2 are equal.

Returns less than zero or greater than zero if str1 is less than or greater than str2 respectively.

Prototype

int memcmp ( const void * ptr1, const void * ptr2, size_t num );

Parameter

This function has the following parameter.

ptr1: Pointer to block of memory.
ptr2: Pointer to block of memory.
num: Number of bytes to compare.

Return

Returns an integral value indicating the relationship between the content of the memory blocks.

Example


#include <stdio.h>
#include <string.h>
/*w  w  w .j av  a 2s  . c  o m*/
int main (){
  char buffer1[] = "this is a test";
  char buffer2[] = "              ";

  int n;

  n=memcmp ( buffer1, buffer2, sizeof(buffer1) );

  if (n>0)
      printf ("'%s' is greater than '%s'.\n",buffer1,buffer2);
  else if (n<0) 
      printf ("'%s' is less than '%s'.\n",buffer1,buffer2);
  else 
      printf ("'%s' is the same as '%s'.\n",buffer1,buffer2);

  return 0;
}

The code above generates the following result.

Example 2


#include <stdio.h>
#include <string.h>
 /*  w ww  .ja va 2s  .c  om*/
void demo(const char* lhs, const char* rhs, size_t sz)
{
    for(size_t n = 0; n < sz; ++n) putchar(lhs[n]);
    int rc = memcmp(lhs, rhs, sz);
    if(rc == 0)
        printf(" compares equal to ");
    else if(rc < 0)
        printf(" precedes ");
    else if(rc > 0)
        printf(" follows ");
    for(size_t n = 0; n < sz; ++n) putchar(rhs[n]);
    puts(" in lexicographical order");
}
 
int main(void)
{
    char a1[] = {'a','b','c'};
    char a2[sizeof a1] = {'a','b','d'};
 
    demo(a1, a2, sizeof a1);
    demo(a2, a1, sizeof a1);
    demo(a1, a1, sizeof a1);
}

The code above generates the following result.