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

You didn't have to repost this, a moderator would have moved your other topic to this forum. But as I said in the other topic:

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*?

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.

Yes, that's correct.

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

Can I see the prototype for your operator<<.

Are you passing a reference to the object or the actual object?

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.

Matrix prod(row,another.col);

'prod' is a local variable of the operator*() function. It is destroyed when the function returns. This:

Code:

return prod;

calls the copy constructor for your class. What does your copy constructor look like?

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?

Your ostream extraction should take a const reference to an object.

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.

I was doing some similar tests:

Code:

#include <iostream>
using namespace std;

class Complex {
   friend ostream& operator<<(ostream&, const Complex&);
   private:
     static int count; 
     int a;
     int b;
     int c;
   public:
     Complex(int i, int j) : a(i), b(j) { c = ++count; }
     ~Complex() { cout << "Destructor called on object " << c << "." << endl; }
     Complex(const Complex& copy) {
          a = copy.a;
          b = copy.b;
          c = ++count;
          cout << "Copy constructor called." << endl;
     }
     Complex operator*(const Complex& operand) {
          Complex three(0,0);
          three.a = a * operand.a;
          three.b = b * operand.b;
          
          return three;
     }
};

ostream& operator<<(ostream& file, const Complex& obj) {
   return file << "(" << obj.a << "-" << obj.b << ")" << endl;
}

int Complex::count = 0;

int main() {
    Complex one(2,4);
    Complex two(8,5);
    cout << one * two;
    
    cin.get();
    return 0;
}

Output:

Code:

(16-20)
Destructor called on object 3.