Question

char *str1 = malloc(256*sizeof(char));
char *str2 = "stack"
for (i=0;i<15;i++){
     sprintf(str1,"%s%s",str1,str2);
} 
printf("%s\n",str1);

I’m trying to concat str2 to str1 at each loop count. But this code segment works but vulnerable.
Whats the best way to concat them?

Answer 1

If you want to use sprintf; something like this:

char *str1 = malloc(256*sizeof(char));
char *str2 = "stack";
*str1 = '\0';
for (i=0;i<15;i++){
    snprintf(str1 + strlen(str1), 256 - strlen(str1), "%s", str2);
} 
printf("%s\n",str1);