尝试使用指针将一个字符串复制到另一个字符串时检测到堆栈崩溃

Question

I am trying to copy one string to another using pointers, but stack smashing error occurred, while the string is copied successfully.

Here's the code below,

#include <stdio.h>
void strcat(char *str1, char *str2) {
    char *run = str1;
    while(*run !='\0')
        run++;
    while(*str2 !='\0') {
        *run = *str2;
        run++;
        str2++;
    }
    *run = '\0';
}
int main() {
    char s[] = "hellomojo";
    char t[] = "world";

    printf("\ns :%s", s);
    printf("\n t :%s",t);
    strcat(s, t);
    printf("\ns after:%s",s);
}

Is it due to illegal access to memory not pointed by pointers?

Answer 1

This char s[]="hellomojo"; is basically the same as char s[10]="hellomojo"; . It is an array of 10 characters (including the NUL-terminator). You cannot store more than 10 characters in it. But you concatenate the other string with this, writing into illegal memory locations beyond the array. This invokes Undefined Behaviour . Hence the stack smashing problem.

The fix would be to increase the size of the first array like:

char s[32] = "hellomojo"; /* 32 chosen arbitrary */

Answer 2

Working with what little code was supplied, my guess would be that at least one of those char pointers doesn't have enough allocated memory, or does not have a null terminating character as expected.

You show the code, but what is the output and the error message? With more information, it would be easier to debug.