字符串的运算符重载

Question

I cannot see whats wrong with the codesnippet below where I try to overload the operator "=". I can build it but not run it (it crashes). Its due to the following syntax in the main method:

string2 = "my world!";

As far as I know - on the left handside of the operator is the object that holds the operator overloaded function and recevies the string-literal (that is passed to the function as an argument) on the right side of the operator.

below is the full code:

#include <iostream>
using namespace std;

class String {

public:
char *string;
String(char *ch) {
    string = ch;
}
String (String &string_obj) {
    string = string_obj.string;
}
String operator=(char *ch) {

    strcpy(string, ch);

    return *this;
}

};

ostream &operator<<(ostream &stream, String obj) {

    stream << obj.string;

    return stream;
}



int main() {

   String string("hello ");
   String string2(string);
   cout << string << string2;

   string2 = "my world!";
   cout << string2;



return 0;
}

Answer 1

you are passing a constant literal in function in this line String string("hello "); and when you are doing strcpy inside String operator=(char *ch) it is trying to modify the content of a constant memory location leading the problem to crash.

you can try by doing this

int main() {
   char str[]="hello";    
   String string(str);
   String string2(string);
   cout << string << string2;

   string2 = "my world!";
   cout << string2;



return 0;
}

Answer 2

In the operator= you are trying to copy the contents of char* to member variable string , but it can be NULL , it may not have enough memory to hold copied string. There are also other problem in you code like not passing const reference to copy constructor etc. I think you should first learn the basics before trying to overload operators.

Answer 3

Your code is broken in many ways. If this is for learning purposes, you should take a look at existing implementations of std::string . If you are planning on using that class in production code: don't , and just use std::string .

Answer 4

Firstly, your String class should have value semantic, and it doesn't. Secondly, you are not allocating any memory for your String.