Returning address to temp var.

[Calthun]

Hi.

I recently wrote a matrix class and overloaded the '()' operator for easy access to the elements. I return the address of the selected element for easy modification.

Then I also thought that you might wanna make the element read-only, anyway this was my solution :

double & CMatrix::operator () (int row, int col)
{
	//Err check omitted	

	if (readOnly)
	{
		double tempVal = elements[row][col];
		return tempVal;
	}
	
	return elements[row][col];
}

I get a warning when I compile (returning address of local variable...) but I don't know if this would be bad/dangerous in this particular case.

Is this a bad way to do it in this case ? If so why, and what would be a better solution ?

[jlou]

Yes, this is a bad solution because the tempVal variable will go out of scope and a reference to garbage will be returned.

A better way to return read-only might be to make a separate function that is const and returns a const reference. That way you have two functions, one that is read-only and one that isn't. The compiler will figure out which one to use as appropriate.

[Jaytan]

You could create two seperate overloads, one that returns the value (and therefor read only) and another that returns a reference to the value in the class.

Returning a reference to a local variable is worthless as it is likely a garbage value as soon as the function goes out of scope.