= operator overloading

This is a discussion on = operator overloading within the C++ Programming forums, part of the General Programming Boards category; Hi, everyone, I overloaded 3 opearators in my Polynomial class, they are "*" which returns the product of two polynomials, ...

  1. #1
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    = operator overloading

    Hi, everyone,

    I overloaded 3 opearators in my Polynomial class, they are

    "*" which returns the product of two polynomials, return type is Polynomial.
    "+" which return the sum of two polynomials, return type is Polynomial.
    "=" which makes the left side have a deep copy of the right side.

    But if I write sum = poly1 + poly2; in the main driver, the compiler gives me error saying illegle operand, i think it's for the "=" operand.
    If I get rid of +poly2, leaving sum = poly1, it works fine. I dont know why. The + sign should perform first, return a Polynomial object, and then the = operator make a deep copy of the return object to the left side sum.

    So how can I make sum = poly1 + poly2 to work? Thanks for the helps.

    Here is the code of the overloaded "="
    Code:
    Polynomial & Polynomial :: operator = (Polynomial & rightSide)
    {    
        if(head != NULL) // Empty the left side Polynomial frist if it's not empty
        {
            for(int i = 0; i < totalTerms; i++)
                deleteFirstNode(head);
        }
        
        rightSide.current = rightSide.head;
        
        for(int i = 0; i < rightSide.totalTerms; i++) // Make deep copy, create a copy of the linked list
        {
            (*this).addTerm(rightSide.current -> getCOEF(), rightSide.current -> getEXP());
            rightSide.current = rightSide.current -> getLink();
        }
        
        return *this;        
    }

  2. #2
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    I just had some trouble with overloading operators, and it seems like the following worked fine (there's probably an easier way to do it that I haven't figured out)
    Code:
    Polynomial& Polynomial::operator=(Polynomial& rightSide)
    {
       // ... rest of function ...
       Polynomial &ref_rightSide = rightSide;
    
       return ref_rightSide;
    }
    That might be something. Other than that, I don't know if I'd be able to help you without seeing some more code.

  3. #3
    Kiss the monkey. CodeMonkey's Avatar
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    Let's see operator + ()
    "If you tell the truth, you don't have to remember anything"
    -Mark Twain

  4. #4
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    The problem might be that your parameter is not a reference to const. When you use operator+ to add poly1 + poly2, the result is a temporary object. But you cannot pass a temporary object to a function that expects a non-const reference.

    The operator= parameter should be const Polynomial &.

    If that's not it, make sure to post text of the full error message(s).

  5. #5
    C++ Witch laserlight's Avatar
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    The copy assignment operator should take a const reference, not a reference, as its parameter. When you make the change, I would expect a compile error from the "rightSide.current = rightSide.head;" statement. What you should do is create current as a local variable, and then use this local variable to traverse rightSide.

    I suggest ignoring aprescott_27's advice. Returning *this is correct behaviour for a copy assignment operator.

    Incidentally, notice that the part where you empty the *this Polynomial is similiar to the destructor, and the part where you make a deep copy is similiar to the copy constructor. You might want to implement the copy assignment operator in terms of the copy constructor, destructor, and a member swap function. The basic idea is to copy the right hand side object to a temporary, and then swap the *this object with the temporary, and let the destructor destroy the temporary that now has the old value of the *this object. A possible implementation would be:
    Code:
    Polynomial& Polynomial::Polynomial(const Polynomial& rhs)
    {
        if (this != &rhs)
        {
            Polynomial temp(rhs);
            swap(temp);
        }
        return *this;
    }
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  6. #6
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    Quote Originally Posted by laserlight View Post
    The copy assignment operator should take a const reference, not a reference, as its parameter. When you make the change, I would expect a compile error from the "rightSide.current = rightSide.head;" statement. What you should do is create current as a local variable, and then use this local variable to traverse rightSide.

    I suggest ignoring aprescott_27's advice. Returning *this is correct behaviour for a copy assignment operator.

    Incidentally, notice that the part where you empty the *this Polynomial is similiar to the destructor, and the part where you make a deep copy is similiar to the copy constructor. You might want to implement the copy assignment operator in terms of the copy constructor, destructor, and a member swap function. The basic idea is to copy the right hand side object to a temporary, and then swap the *this object with the temporary, and let the destructor destroy the temporary that now has the old value of the *this object. A possible implementation would be:
    Code:
    Polynomial& Polynomial::Polynomial(const Polynomial& rhs)
    {
        if (this != &rhs)
        {
            Polynomial temp(rhs);
            swap(temp);
        }
        return *this;
    }
    Thanks for the help. I fixed it using your suggestion. Thanks.

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