Rotating image using classes - c++

Question

I'm having trouble rotating an image 90 degrees, the images are 768 x 768 pixels. The code I have shown here is able to create a new image, but the function I've written isn't manipulating it at all. My image class and function that's in the driver to rotate it is below. I have to rotate all the pictures 90 degrees clockwise and counterclockwise; I think my issue is trying to get the pointers to correctly switch the pixels around.
class image {
public:
image(); //the image constructor (initializes everything)
image(string filename); //a image constructor that directly loads an image from disk
image(image &other); //copy constructor
~image(); //the image destructor (deletes the dynamically created pixel array)
pixel** getPixels(); //return the 2-dimensional pixels array
int getWidth(); //return the width of the image
int getHeight(); //return the height of the image
void createNewImage(int width, int height);
private:
pixel** pixels; // pixel data array for image
int width, height; // stores the image dimensions
void pixelsToCImage(CImage* myImage);
};
void RotateClockWise(image *imageIn)
{
image rotateImg;
image *ptr = (image*) &rotateImg;
*ptr = *imageIn;
int height = rotateImg.getHeight();
int width = rotateImg.getWidth();
pixel** rotatePix = rotateImg.getPixels();
for (int i = 0; i < height; i++)
{
for (int j = 0; j < width; j++)
{
rotatePix[i][j] = rotatePix[j][i];
*(ptr + j * height + (height - i - 1)) = *(ptr + i * width + j);
}
}
}

Answer 1

First your code is very c style. This is cool, I love this kind of coding, but you can make your life easier with references.
Solution for your code:
You never set point to imageIn, just the copy the value from image in to rotateImg:
image rotateImg;
image *ptr = (image*) &rotateImg;
*ptr = *imageIn;
This means you just modify the local variable rotateImg and not the object which is given by the pointer.
And here just a plain NO:
ptr points on an image. Each +j means "go to the next image" or more precissly: ptr = ptr + sizeof(image); which should be around 12 bytes + vtable. Dont do this. You You can just do this when you loop over an 1 dimensional pixel array.
*(ptr + j * height + (height - i - 1)) = *(ptr + i * width + j); //BAD
Here is some C style code which solves the problem. I did not know you could give a 2 dimensional array via a double pointer **ptr (indirect pointers).
void RotateClockWise(image* imageIn)
{
image rotateImg;
rotateImg = *imageIn;
image *ptr = imageIn;
int height = rotateImg.getHeight();
int width = imageIn->getWidth();
pixel** normalPix = rotateImg.getPixels();
pixel** rotatePix = imageIn->getPixels();
for (int i = 0; i < height; i++)
{
for (int j = 0; j < width; j++)
{
rotatePix[i][j] = normalPix[(height-1)-j][(width-1)-i];
}
}
}
I am to lazy to code it in C++ Style, but have a look at the Reference
void RotateClockWise(image& imageIn)

Answer 2

You have imageIn argument that probably points to image you want to rotate. However, you create rotateImg object, get pointer to this object (ptr) and duplicate imageIn to this ptr. So, now you manipulate image copy instead of image itself, that is why object pointed by imageIn never changes its value.