Why is destructor being called??

This is a discussion on Why is destructor being called?? within the C Programming forums, part of the General Programming Boards category; Hello all, I have created a dynamic matrix class. I overloaded the multiplication operator as follows: Code: Matrix Matrix::operator*(const Matrix ...

  1. #1
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    Why is destructor being called??

    Hello all,

    I have created a dynamic matrix class. I overloaded the multiplication operator as follows:

    Code:
    Matrix Matrix::operator*(const Matrix &another) const //'const' keyword after => doesn't
    {														//modify data members
    	if (col != another.row)
    	{
    		cout<<"Error in matrix multiplication. Matrix dimensions do not agree."<<endl;
    		return *this;
    	}
    
    	Matrix prod(row,another.col);
    	Complex sum(0,0);
    
    	for(int i=0; i<row; i++)		//i: 0 to 3
    	{
    		sum = 0;
    		for(int j=0; j<another.col; j++)	//j: 0 to 2
    		{
    			for(int k=0; k<row; k++)
    			{
    				sum = sum + A[i][k] * another(k,j);
    			}
    			//cout<<"prod("<<i<<","<<j<<") = "<<sum<<endl;
    			prod(i,j) = sum;
    		}
    	}
    	return prod;
    }
    I wanted to do it in such a way that if I do

    Code:
    Matrix A(5,5), B(5,1);
    //define the matrices
    cout<<A*B<<endl;   //I overloaded the cout operator as well
    Just for the record, I created a complex number class, and I have defined a similar function:

    Code:
    Complex Complex::operator +(const Complex &num) const
    {
    	Complex sum;
    	sum.real = real + num.real;
    	sum.imag = imag + num.imag;
    	return sum;				
    }
    When I do

    Code:
    Complex a(1,1), b(2,-2);
    cout<<a+b<<endl;
    The destructor is called after it is displayed. But this does not work for the Matrix class, and I just can't figure out why. I thought I would save you all the trouble of going through all the code by only displaying what is pertinent. If you need all the code, pls let me know. Thanks

    Bill

  2. #2
    Registered User ssharish2005's Avatar
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    Bill u was suppose to post this on C++ form not in here. showing a bit more code of your would help us

    ssharish2005

  3. #3
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    Oh I'm sorry. I must have came here by mistake. Thanks.

  4. #4
    ATH0 quzah's Avatar
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    C++ is a 'by value' language. The variable 'prod' is a local variable. Thus, the local copy is destroyed when the function ends, and it returns a copy of it. Thus, the destructor of 'prod' is called; it also creates a new copy, and returns it. Or at least I believe that's what's happening. I don't use C++ really ever.


    Quzah.
    Hope is the first step on the road to disappointment.

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    But why is it working with the Complex function and not with the matrix function?

  6. #6
    Devil's Advocate SlyMaelstrom's Avatar
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    You're saying that on this line:
    Code:
    sum = sum + A[k] * another(k,j); // In your overloaded operator*
    the destructor is never called on the variable in your operator+? Nor is it called on the two temp variables in your operator*?
    Last edited by SlyMaelstrom; 03-19-2006 at 09:12 PM.
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    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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