Operator overloading - creation of a new String-class

Question

I am near giving up right now - headache and red eyes. Some of you will probably downvote this question but I have no alternative. I am not lazy but have no one to talk to.

Its all about making my own String-class in c++ where one can be able to concatenate strings, send another string object into the strings constructor, or send string-literals to the constructor.

The program is supposed to output the following:

 hello hello2 
 much hedache!!!
 Enter a name: 
 hello John

Instead the program is producing the following:

 hello hello2 
 much hedache!!!
 Enter a name: 
 much headache John

For somereason the string "much headache" is kept in the object - not substituted with a concatenation of string and string3.

string2 = "much hedache!!!";

And I have noticed that this is somehow caused when I send a string object to the constructor.

 String string2(string);

If I now change this to the following:

String string2("hello2");

it works.

I cannot figure out why, would be very delighted of someone could answer this.

#include <iostream>
using namespace std;

class String {

public:
char *string;
String(char *ch) {
    string = new char[strlen(ch)];

    int i = 0;
    for(char *temp_ch_ptr = ch; *temp_ch_ptr; ++temp_ch_ptr) {
        string[i] = *temp_ch_ptr;
        i++;
    }

}
String() {
    string = new char[100];
}

String (String &string_obj) {

    string = new char[strlen(string_obj.string)];

    string = string_obj.string;
}

String operator=(char *ch) {

    strcpy(string, ch);

    return *this;
}

String operator+(String obj) {

    String temp;
    strcpy(temp.string, string);
    strcat(temp.string, obj.string);

    return temp;
}

};

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

    stream << obj.string;

    return stream;
}

istream &operator>>(istream &stream, String obj) {

cout << "Enter a name: ";
stream >> obj.string;

return stream;
}



int main() {

  String string("hello ");
  //String string2("hello2 ");
  String string2(string);
  cout << string << string2 << endl;

  string2 = "much hedache!!!";

  cout << string2 << endl;

  String string3;

  cin >> string3;
  string2 = string + string3;
  cout << string2 << endl;

return 0;
}

I am not sure about the copy-constructor - could the problem be there?

You'll need to keep track of the actual string length in your class! Also relevant: http://stackoverflow.com/questions/4172722/what-is-the-rule-of-three — πάντα ῥεῖ, May 03 '14 at 15:18

score 2 · Answer 1 · answered May 03 '14 at 15:23

I am not sure about the copy-constructor - could the problem be there?

Yes, absolutely. It doesn't work at all.

string = new char[strlen(string_obj.string)];

Here you create a new array of the same length as the existing string.

string = string_obj.string;

And here you completely throw away that new array (leaving it dangling as a memory leak) then set the new string object's pointer to be the same as the old string object's pointer.

You need to do a deep copy; I suggest std::copy.

Also this copy constructor should take const String&, not String&; similarly, your char* constructor should actually take const char* if you want passing in string literals to be valid.

thanks - working hard on this right now. Is the solution to the problem only in the copy-constructor? What about the memberfunction where the operator "=" is overloaded? — user2991252, May 03 '14 at 20:11

score 1 · Answer 2 · answered May 03 '14 at 15:26

Your program has both a bug and a memory leak. In the copy constructor you allocate memory but new use, instead just point to the passed string's memory. You should copy the content of passed string to newly allocated memory. As a result the allocated memory is lost. Also you dont provide any destructor to de-allocate the memory.

String (String &string_obj) {

  string = new char[strlen(string_obj.string)];

  strcpy(string,string_obj.string);
}

~String(){delete string;}

Operator overloading - creation of a new String-class

2 Answers2