strncat Function

Append a specified number of characters from the source string to the destination string.

Include

<string.h>

Prototype

char *strncat(char *s1, const char *s2, size_t n);

Arguments

s1

destination string to copy to

s2

source string to copy from

n

number of characters to append

Return Value

Returns a pointer to the destination string.

Remarks

This function appends up to n characters (a null character and characters that follow it are not appended) from the source string to the end of the destination string. If a null character is not encountered, then a terminating null character is appended to the result. If the strings overlap, the behavior is undefined.

Example

#include <string.h>
#include <stdio.h>

int main(void)
{
  char buf1[50] = "We're here";
  char buf2[50] = "Where is the time?";
  char buf3[50] = "Why?";

  printf("buf1 : %s\n", buf1);
  printf("\t(%d characters)\n\n", strlen(buf1));
  printf("buf2 : %s\n", buf2);
  printf("\t(%d characters)\n\n", strlen(buf2));
  printf("buf3 : %s\n", buf3);
  printf("\t(%d characters)\n\n\n", strlen(buf3));

  strncat(buf1, buf2, 6);
  printf("buf1 after strncat of 6 characters "
         "of buf2: \n\t%s\n", buf1);
  printf("\t(%d characters)\n", strlen(buf1));
  printf("\n");

  strncat(buf1, buf2, 25);
  printf("buf1 after strncat of 25 characters "
         "of buf2: \n\t%s\n", buf1);
  printf("\t(%d characters)\n", strlen(buf1));
  printf("\n");

  strncat(buf1, buf3, 4);
  printf("buf1 after strncat of 4 characters "
         "of buf3: \n\t%s\n", buf1);
  printf("\t(%d characters)\n", strlen(buf1));
}

Example Output

buf1 : We’re here
        (10 characters)

buf2 : Where is the time?
        (18 characters)

buf3 : Why?
        (4 characters)

buf1 after strncat of 6 characters of buf2:
        We’re hereWhere
        (16 characters)

buf1 after strncat of 25 characters of buf2:
        We’re hereWhere Where is the time?
        (34 characters)

buf1 after strncat of 4 characters of buf3:
   We’re hereWhere Where is the time?Why?
        (38 characters)