Never trust a C++ function that return char *

gistfile1.txt

#include <iostream>

/**
 * You can run online at http://code.hackerearth.com/
 */

using namespace std;

const char *doubleString(const char *s){
        string ss = string(s) + string(s);
        return ss.c_str();
}

int main() {
        const char *hello = "hello";
        const char *hellox2 = doubleString(hello);
        cout << "It should be \"" << hello << hello << "\"" << " actual: " << hellox2 << endl;
        doubleString("dummy");
        cout << "It should be \"" << hello << hello << "\"" << " actual: " << hellox2 << endl;
        
        return 0;
}