I need some help...

[tex1ntux]

Can someone offer some insight to help correct this piece of code?

TwoDShape *shapes[5];
 
    shapes[0] = &Triangle("right", 8.0, 12.0);
    shapes[1] = &Rectangle(10);
    shapes[2] = &Rectangle(10, 4);
    shapes[3] = &Triangle(7.0);
    shapes[4] = &TwoDShape(10, 20, "generic");

The compiler says "[Warning] taking address of temporary" for each of the shapes assignments. I think I can see the problem, I'm just a newbie (this is a code snippet from a c++ intro book), and I don't know to fix it.

Thanks.

[Ganon11]

Maybe you should split each line like:

shapes[0] = &Triangle(whatev);

to

Triangle *temp = new Triangle(whatev);
shapes[0] = temp;

I think your code is creating the object, getting its address, and then setting that address to the array - but when the function exits, the temporary object that was created is deleted. You need to create the object using new so that it won't be deleted when the function exits.

You may also be able to write

shapes[0] = new Triangle(whatev);

but without testing, I couldn't be sure.

[tex1ntux]

This solution worked:

shapes[0] = new Triangle(whatev);

The book I'm using doesn't even cover the new operator until the last chapter (I checked the index), so I never would have guessed to use it.

Thank you. :)

[Ganon11]

Odd that your book would include this code, but not realize the error being generated. Perhaps this is included in main() and not a function, in which case the warning never causes a problem? In any case, it's good that you figured it out.

[lqdeffx]

Do not forget, if you are going to use the "new" operator, it must be accompanied with the "delete" operator as well. Otherwise, memory leaks can occur.

[tex1ntux]

This code was in main(), and the program compiled, but the output was totally screwy. It was supposed to output this:

Object is triangle
Area is 48
 
Object is rectangle
Area is 100
 
Object is rectangle
Area is 40
 
Object is triangle
Area is 24.5
 
Object is generic
Error: area() must be overridden.
Area is 0

Using this loop (where area() is a virtual function from the base class that should be overridden by triangle or rectangle's area()):

for(int i=0; i < 5; i++) {
            cout << "Object is " <<
                 shapes[i]->getName() << "\n";
 
            cout << "Area is " << 
                 shapes[i]->area() << "\n";
 
            cout << "\n";
            }

But before I added the new operator, the output was this:

Object is generic
Error: area() must be overridden.
Area is 0
 
Object is generic
Error: area() must be overridden.
Area is 0
 
Object is generic
Error: area() must be overridden.
Area is 0
 
Object is generic
Error: area() must be overridden.
Area is 0
 
Object is generic
Error: area() must be overridden.
Area is 0