Thread: Returning address to temp var.

  1. #1
    Registered User
    Join Date
    Nov 2002

    Returning address to temp var.


    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 ?

  2. #2
    Registered User jlou's Avatar
    Join Date
    Jul 2003
    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.

  3. #3
    Registered User
    Join Date
    Mar 2004
    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.

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