Question

Today I was met the following code block:

#include <iostream>
using namespace std;
char *return_char_array(const char *cptr)
{
    char charArray[100] = {0};
    strcpy(charArray, cptr);
    return charArray;
}
int main()
{
    const char *cptr = "test";

    char localCharArray[100] = {0};
    strcpy(localCharArray, return_char_array(cptr)); // output "test"
    cout<<localCharArray<<endl;

    string s = return_char_array(cptr);              // corrupt output
    cout<<s<<endl; 

    return 0;
}

At the first sight I thought both the output would be corrupt but surprisingly the first output is “test” while the second is corrupt. Would someone tell me why?

Answer 1

They are both corrupt. Just because it appears to work, doesn’t mean it’s ok.

This is undefined behavior, anything can happen, including appearing to work.