Question

I wrote the following code for string concatnation using pointers in C

#include<stdio.h> 
#include<stdlib.h>
#include<string.h>
void strCat(char *str1,char *str2);
int main(void)
{
char str1[] = "Rohit";
char str2[] = "Kumar";  
strCat(str1,str2);
return 0;
}

void strCat(char *str1,char *str2)
{
int i;
char *start;
start = str1;
printf("%s",str1);
while(*str1++ != '\0')
    continue;
while(*str2 != '\0')
    *str1++ = *str2++;
*str1 = '\0';

printf("%s\n",str1);
}

Why the ouput is Rohit(null). Please Help!!

Answer 1

Well, first of all str1 isn’t long enough to fit both strings.

Here

while(*str2 != '\0')
    *str1++ = *str2++; /* You are overstepping str1 -> undefined behavior */

There are other problems with the code. Perhaps you should try the string.h strcat instead ?