problems with overloaded '+' again

Ok look , i have a simple string class with overloaded '+=' , '=' and '+'. The '+=' and '=' work just fine when i use them with object. But the friggin '+' sign is still causing troubles !!! :mad:

I spent like 1 hour on this crap and i still can't figure out how to get around this "Debug Assertion Failed" error (vc++). I tracked execution and found that the problem occurs when one of the objects (don't know which) tries to delete it's sPtr space.

anyway , the following are my .h , .cpp and main.cpp files. The problem is probably in the operator+ function (hilihgted in blue) , i posted the whole code just incase you need to take a look at something else :

mystr.h

Code:

---

#ifndef MYSTR_H
#define MYSTR_H

class mystr
{
public :
        mystr(const char * = "");
        ~mystr();
       
        const mystr &operator+=(const mystr &);
        const mystr &operator=(const mystr &);

        mystr operator+(const mystr &);

        void print();

private :
        int length;
        char *sPtr;
};

#endif

---

mystr.cpp

Code:

---

#include <iostream>
using std::cout;
using std::endl;

#include <cstring>
#include "mystr.h"

mystr::mystr(const char *s) // default constructor
{
        length = strlen(s);
        sPtr = new char[ length + 10 ];

        strcpy(sPtr, s);
}


mystr::~mystr()  // destructor
{
        delete [] sPtr;
}


const mystr &mystr::operator +=(const mystr &right)
{
        size_t newLength = length + right.length;

        char *tempPtr = new char[newLength + 1];

        strcpy(tempPtr, sPtr);
        strcpy(tempPtr + length, right.sPtr);
       
        delete [] sPtr;

        sPtr = tempPtr;
        length = newLength;

        return *this;
}


mystr mystr::operator+(const mystr &right)
{
        mystr temp(sPtr);

        temp += right;

        return temp;

}


const mystr &mystr::operator=(const mystr &right)
{
        if( &right != this)
        {
                delete [] sPtr;

                sPtr = new char[right.length + 1];

                strcpy(sPtr, right.sPtr);
        }

        return *this;
}



void mystr::print()
{
        cout << sPtr << endl;
}

---

main.cpp

Code:

---

#include "mystr.h"

int main(void)
{
        mystr a("hello"), b("world\n"), c;

        a.print();

        b.print();

        c = a + b;

        c.print();

        return 0;
}

---

it only displays :

hello
world

then shows an error. I hope someone can help before i tear the rest of my hair out.

p.s : please don't give examples , just show me how to fix my my code.

I've had the same problem before too....The problem's in that when returning the temporary string, the destructor gets called, but AFTER the string is returned, so you end up returning a string with an old, dead pointer value that's just been deleted!

*pulls hair out*

The only thing I can think of is a method which involves creating, dynamically, a new string and returning the pointer to it....but this will end up creating a memory leak :confused:

Your code seems fine, you just need to add a copy constructor.

Ah hah! So it's just a matter of using the same copy constructor as the overloaded operator is using? As in, in this case, the + operator's using a mystr&, so use a copy constructor that accepts a mystr&

That's what I just did in the above code and the crash disappeared.

Code:

---

mystr::mystr(const mystr &s)
{
        length=s.length;
        sPtr = new char[ length + 1 ];

        strcpy(sPtr, s.sPtr);
}

---

Code:

---

mystr mystr::operator+(const mystr &right)
{
        mystr temp(*this);

        temp += right;

        return temp;
}

---

Oh, nevermind, the copy constructor's called when the return statement is hit.

yea i just need to add a copy constructor to the original code. Thanks alot Daved and Jeff. If you were girls , i'd fall in love with you both :p

Quote:

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Originally Posted by Brain Cell

I spent like 1 hour on this crap and i still can't figure out how to get around this "Debug Assertion Failed" error (vc++). I tracked execution and found that the problem occurs when one of the objects (don't know which) tries to delete it's sPtr space.

---

Why? I told you yesterday that you needed a copy constructor. :rolleyes:

Remember the rule of three: If you implement either the copy constructor, destructor or assignment operator, you should probably implement all three.

Please remember to keep threats of violence out of your thread titles.

This is how I implemented my + operator for my little string class

Code:

---

//.h
friend string operator+(const string &s, const string &s2);
friend string operator+(const char *s, const string &s2);
friend string operator+(const char ch, const string &s2);
friend string operator+(const string &s, const char *s2);
friend string operator+(const string &s, const char ch);

---

Code:

---

//.cpp
    string operator+(const string &s, const string &s2)
    {
        string both = s;
        both += s2;
        return both;
    }
    string operator+(const char *s, const string &s2)
    {
        string both = s;
        both += s2;
        return both;
    }
    string operator+(const char ch, const string &s2)
    {
        string both(1,ch);
        both += s2;
        return both;
    }
    string operator+(const string &s, const char *s2)
    {
        string both = s;
        both += s2;
        return both;
    }
    string operator+(const string &s, const char ch)
    {
        string both = s;
        both += ch;
        return both;
    }

---

Quote:

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Originally Posted by pianorain

Why? I told you yesterday that you needed a copy constructor. :rolleyes:

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ooh , sorry. Seems like i skipped that line :o

Quote:

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Originally Posted by joshdick

Remember the rule of three: If you implement either the copy constructor, destructor or assignment operator, you should probably implement all three.

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Useful tip , thanks :).

Quote:

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Originally Posted by Thantos

Please remember to keep threats of violence out of your thread titles.

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ummm...ok. But you knew i wasn't serious right ;)? i was only expressing how ***** off i was.