strncat() — Concatenate 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>

char *strncat(char * __restrict__string1, const char * __restrict__string2, size_t count);

General description

The strncat() built-in function appends the first count characters of string2 to string1 and ends the resulting string with a NULL character (\0). If count is greater than the length of string2, strncat() appends only the maximum length of string2 to string1. The first character of the appended string overwrites the terminating NULL character of the string pointed to by string1.

If copying takes place between overlapping objects, the behavior is undefined.

Returned value

strncat() returns the value string1, the concatenated string.

Example

CELEBS44

⁄* CELEBS44                                      

   This example demonstrates the difference between &strcat. and                
   &strncat..                                                                   
   &strcat. appends the entire second string to the first,                      
   whereas &strncat. appends only the specified number of                       
   characters in the second string to the first.                                
                                                                                
  *⁄                                                                            
#include <stdio.h>                                                              
#include <string.h>                                                             
                                                                                
#define SIZE 40                                                                 
                                                                                
                                                                                
int main(void)                                                                  
{                                                                               
  char buffer1[SIZE] = "computer";                                              
  char * ptr;                                                                   
                                                                                
  ⁄* Call strcat with buffer1 and " program" *⁄                                 
                                                                                
  ptr = strcat( buffer1, " program" );                                          
  printf( "strcat : buffer1 = \"%s\"\n", buffer1 );                             
                                                                                
  ⁄* Reset buffer1 to contain just the string "computer" again *⁄               
                                                                                
  memset( buffer1, '\0', sizeof( buffer1 ));                                    
  ptr = strcpy( buffer1, "computer" );                                          
                                                                                
  ⁄* Call strncat with buffer1 and " program" *⁄                                
  ptr = strncat( buffer1, " program", 3 );                                      
  printf( "strncat: buffer1 = \"%s\"\n", buffer1 );                             
}

Output

strcat : buffer1 = "computer program"
strncat: buffer1 = "computer pr"