Thread: 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[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 I could do this:

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 a million.

Bill

I am saying that the destructor is called. But for some reason, when I do

Code:

Complex a, b;
cout<<a+b<<endl; //after assigning values to a and b

It is called after the result is displayed. When the code is as follows:

Code:

Matrix A, B;
cout<<A*B<<endl; //after assigning values to A and B

the destructor is called before A*B is displayed, so that part is essentially blank.

Am I even going about this the right way? If you do

Code:

int a = 9;
cout<<a+5<<endl;
cout<<a<<endl;

then the output should be

Code:

14
9

i.e. the value of a is not supposed to change after you do a+5. That is why I am creating an extra variable prod and not returning *this. I do not want the contents to be modified unless an assignment operator is used.

So no idea why I can't display A*B (with A and B being matrices)?

Sure. Here is the code:

Code:

ostream& operator <<(ostream &out, Matrix &a)
{
	for (int i=0; i<a.row; i++)
	{
		for (int j=0; j<a.col; j++)
		{
			out<<a(i,j)<<"		";
		}
		out<<endl;
	}
	return out;
}

I am passing and returning by reference.

I understand that it is destroyed. My question is why is it destroyed before it is displayed? Why not after, as is the case with Complex objects?

Code:

#include <iostream>
using namespace std;


class Test
{
public:
	Test()
	{
		a = 10;
	}

	~Test()
	{
		cout<<"Test destructor called."<<endl;
	}

	friend ostream& operator<<(ostream& out, const Test& obj);

private:
	int a;
};

ostream& operator<<(ostream& out, const Test& obj)
{
	out<<obj.a;
	return out;
}

Test someFunc()
{
	Test a;
	return a;
}

int main()
{
	
	cout<<someFunc()<<endl;

	return 0;
}

output:

Test destructor called.
10
Test destructor called.

You mean like this?

Code:

ostream& operator <<(ostream &out, Matrix const &a)
{
	for (int i=0; i<a.row; i++)
	{
		for (int j=0; j<a.col; j++)
		{
			if((bool)a == false)
				a(i,j).SetFreqMode(false);
			out<<a(i,j)<<"		";
		}
		out<<endl;
	}
	return out;
}

Thanks for the input. I tried it, but it still didn't work.

Thanks 7stud. My output however would have the "Destroying ..." message before and after, but no 10.