strncmp() — Compare strings

Standards

Standards / Extensions	C or C++	Dependencies
ISO C POSIX.1 XPG4 XPG4.2 C99 Single UNIX Specification, Version 3	both

Format

#include <string.h>

int strncmp(const char *string1, const char *string2, size_t count);

General description

The strncmp() built-in function compares at most the first count characters of the string pointed to by string1 to the string pointed to by string2.

The string arguments to the function should contain a NULL character (\0) marking the end of the string.

The relation between the strings is determined by the sign of the difference between the values of the leftmost first pair of characters that differ. The values depend on character encoding. This function is not locale sensitive.

Returned value

strncmp() returns a value indicating the relationship between the substrings, as follows:

Value: Meaning
< 0: String pointed to by substring1 less than string pointed to by substring2
= 0: String pointed to by substring1 equivalent to string pointed to by substring2
> 0: String pointed to by substring1 greater than string pointed to by substring2

Example

CELEBS45

⁄* CELEBS45                                      

   This example demonstrates the difference between &strcmp.                    
   and &strncmp..                                                               
                                                                                
 *⁄                                                                             
#include <stdio.h>                                                              
#include <string.h>                                                             
                                                                                
#define SIZE 10                                                                 
                                                                                
int index = 3;                                                                  
                                                                                
int main(void)                                                                  
{                                                                               
  int  result;                                                                  
  char buffer1[SIZE] = "abcdefg";                                               
  char buffer2[SIZE] = "abcfg";                                                 
  void print_result( int, char *, char * );                                     
                                                                                
  result = strcmp( buffer1, buffer2 );                                          
  printf( "  strcmp: compares each character\n");                               
  print_result( result, buffer1, buffer2 );                                     
                                                                                
  result = strncmp( buffer1, buffer2, index);                                   
  printf( "\nstrncmp: compares only the first %i characters\n", index );        
  print_result( result, buffer1, buffer2 );                                     
}                                                                               
                                                                                
void print_result( int res, char * p_buffer1, char * p_buffer2 )                
{                                                                               
  if ( res == 0 )                                                               
    printf( "first %i characters of \"%s\" is identical to \"%s\"\n",           
             index,  p_buffer1, p_buffer2);                                     
  else if ( res < 0 )                                                           
    printf( "\"%s\" is less than \"%s\"\n", p_buffer1, p_buffer2 );             
  else                                                                          
    printf( "\"%s\" is greater than \"%s\"\n", p_buffer1, p_buffer2 );          
}

Output

  strcmp: compares each character
  "abcdefg" is less than "abcfg"

  strncmp: compares only the first 3 characters
  first 3 characters of "abcdefg" is identical to "abcfg"