Question

I have a class which allocates memory on the heap and then the destructor frees it. My copy constructor is never being called for some reason and I do not understand why. Here is my implementation:

 AguiBitmap::AguiBitmap( const AguiBitmap &bmp )
    {

        this->nativeBitmapPtr = al_clone_bitmap(bmp.nativeBitmapPtr);
    }

    AguiBitmap::AguiBitmap( char *filename )
    {

        if(!filename)
        {
            nativeBitmapPtr = 0;
            return;
        }

        nativeBitmapPtr = al_load_bitmap(filename);

        if(nativeBitmapPtr)
        {

            width = al_get_bitmap_width(nativeBitmapPtr);
            height = al_get_bitmap_height(nativeBitmapPtr);
        }
        else
        {
            width = 0;
            height = 0;
        }
    }




    ALLEGRO_BITMAP* AguiBitmap::getBitmap() const
    {
        return nativeBitmapPtr;
    }

However,
When I do something like:

AguiBitmap bitmap;
bitmap = AguiBitmap("somepath");

The copy constructor code is never called (set a breakpoint). And therefore, my issue of having an invalid pointer in the reconstructed object from the temporary object becomes invalid when the temporary one is destroyed.

What do I do to get my copy constructor to be called?

Thanks

Answer 1

That bit of code wont invoke the copy constructor – it invokes the assignment operator (or the copy-assignment operator):

// a helper `swap` function
void AguiBitmap::swap(AguiBitmap& a, AguiBitmap& b)
{
    using std::swap;  // enable the following calls to come from `std::swap`
                      // if there's no better match

    swap(a.nativeBitmapPtr, b.nativeBitmapPtr);
    swap(a.width, b.width);
    swap(a.height,b.height);
}

AguiBitmap::AguiBitmap& operator=( const AguiBitmap &rhs )
{
    // use copy-swap idiom to perform assignment
    AguiBitmap tmp(rhs);

    swap( *this, tmp);
    return *this;
}

Also note that your copy constructor is incomplete, since the height and width members aren’t being copied:

width = bmp.width;
height = bmp.height;