strncat : strncat « string.h « C Tutorial

Item	Value
Header file	string.h
Declaration	char strncat(char str1, const char *str2, size_t count);
Function	concatenates not more than count characters of str2 to str1 and terminates str1 with a null.
Return	returns *str1.

You have to ensure that str1 is large enough to hold both its str1 and str2.

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

  int main(void)
  {
    char s1[80], s2[80];
    unsigned int len;

    gets(s1);
    gets(s2);


    len = 79-strlen(s2);
    strncat(s2, s1, len);
    printf(s2);

    return 0;
  }

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24.14.strncat
	24.14.1.	strncat
	24.14.2.	Using strcat and strncat