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Pointers with Images Help

maninbluerobe (5)
I get a memory access violation when I run the below code. void createNewImage(int width, int height); this function deletes any current image data and creates a new image with the specified width/height and allocates the needed number of pixels dynamically. The new image contains four blocks with different color, red, blue, green, and black. I'm really having a lot of trouble with this one I cant get my head around images with pointers.

Thanks


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#include <iostream>
#include "image.h"


image::image() 
{
	pixels = NULL;
	width = 0;
	height = 0;
}

image::image(string filename) 
{
	pixels = NULL;
	width = 0;
	height = 0;
	loadImage(filename);
}

image::image(image &other)
{
	

}
image::~image()
{
	for (int i = 0; i < height; i++)
		delete[]this->pixels[i];
	delete[]this->pixels;
}

int image::getWidth()
{
	return this->width;
}

int image::getHeight()
{
	return this->height;
}

pixel** image::getPixels()
{
	return this->pixels;
}

void image::createNewImage(int width, int height)
{

	for (int i = 0; i < height; i++)
		delete[]this->pixels[i];
	delete[]this->pixels;

	//provide the code for this function
	pixel **p = new pixel*[width];

	for (int i = 0; i < width; i++)
		p[i] = new pixel[width];

	//for (int j = 0; j < height; j++)
		//p[j] = new pixel[height];



	for (int i = 0; i < width; i++)
	{

		for (int j = 0; j < height; j++)
		{

			p[i][j].red=255;
			p[i][j].blue=0;
			p[i][j].green = 0;
			
		}

	}
	this->pixels = p;
}







//-------------------------------------------Please do not touch the following functions---------------------------------
bool image::loadImage(string filename)
{
	if(pixels)
	{
		for(int i=0; i<height; i++)
			delete [] pixels[i];
		delete [] pixels;
		pixels = NULL;
		width = 0;
		height = 0;
	}
	
	CImage myImage;
	CString cs(filename.c_str());
	myImage.Load(cs);
	
	if(myImage.IsNull())
	{
		cout << "The requested image could not be loaded." << endl;
		return false;
	}
	if(myImage.GetBPP() != 24) 
	{
		cout << "The input image must be stored in the 8 bit RGB (24 bpp) colorspace." << endl;
		return false;
	}

	width = myImage.GetWidth();
	height = myImage.GetHeight();

	pixels = new pixel*[height];
	uchar* imageBuf = (uchar*)myImage.GetBits();
	int scanline = myImage.GetPitch();

	for (int j = 0; j < height; j++) 
	{
		pixels[j] = new pixel[width];	
		for (int i = 0; i < width; i++) 
		{
			pixels[j][i].red = imageBuf[j*scanline+i*3+2];
			pixels[j][i].green = imageBuf[j*scanline+i*3+1];
			pixels[j][i].blue = imageBuf[j*scanline+i*3];
		}
	}
	return true;
}

void image::pixelsToCImage(CImage* myImage)
{
	myImage->Create(width, height, 24, 0);
	if (myImage->IsNull()) {
		cout << "An error occured when creating a new image!" << endl;
		return;
	}

	uchar* imageBuf = (uchar*)myImage->GetBits();
	int scanline = myImage->GetPitch();
	for (int j = 0; j < height; j++) 
		for (int i = 0; i < width; i++) 
		{
			imageBuf[j*scanline+i*3] = pixels[j][i].blue;
			imageBuf[j*scanline+i*3+1] = pixels[j][i].green;
			imageBuf[j*scanline+i*3+2] = pixels[j][i].red;
		}
}

void image::saveImage(string filename) 
{
	if(!pixels)
	{
		cout << "No image data has been created to save! (The pixel buffer is empty)" << endl;
		return;
	}

	CImage myImage;
	pixelsToCImage(&myImage);

	CString cs(filename.c_str());
	myImage.Save(cs);

	return;
}
kbw (9488)
There's lots of code there, and without showing declarations of things--the declarations aren't irrelevant details, they're absolutely essential.

Looking from the top I saw this error. You should be using the height version of the loop.
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	//provide the code for this function
	pixel **p = new pixel*[width];

	for (int i = 0; i < width; i++)
		p[i] = new pixel[width];

	//for (int j = 0; j < height; j++)
		//p[j] = new pixel[height];
maninbluerobe (5)
.h
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#ifndef IMAGE
#define IMAGE

#include <atlimage.h>
#include <string>
#include <cstdlib>
#include "pixel.h"

using namespace std;
typedef unsigned char uchar;
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); //this function deletes any current image data and creates a new image
													//with the specified width/height and allocates the needed number of pixels
													//dynamically. The new image contains four blocks with different color, red, blue, green, and black.
		
		//following two functions are provided.
		bool loadImage(string filename);		//load an image from the specified file path.  Return true if it works, false if it is not a valid image.
												//Note that we only accept images of the RGB 8bit colorspace!
		void saveImage(string filename);	   //Save an image to the specified path


			
	private:
		pixel** pixels;				// pixel data array for image 
		int width, height;		// stores the image dimensions 

		void pixelsToCImage(CImage* myImage);  //this function is called internally by the image class.
												//it converts our pixel struct array to a standard BGR uchar array with word spacing.
												//(Don't worry about what this does)
		
		

};

#endif
kbw (9488)
Did you fix that 2D array and rerun?

Where does the program crash? If you don't know, run it in a debugger and take a look at the call stack.
maninbluerobe (5)
access violation here imageBuf[j*scanline+i*3] = pixels[j][i].blue;

and i changed it to this
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	//provide the code for this function
	pixel **p = new pixel*[width];

//	for (int i = 0; i < width; i++)
	//	p[i] = new pixel[width];

	for (int j = 0; j < height; j++)
		p[j] = new pixel[height];
maninbluerobe (5)
here is the rest

pixel.h
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//A POD class (Plain Old Data Class) to hold one pixel's worth of data.  (Assuming the pixel is 24bpp and RGB)
//Note:  Not having getters and setters for the members of a class is only acceptable if you are using it as a Plain Old Data Class.
//If your class has any constructors, destructors, static members, virtual functions, derivations, or anything that is not a public
//data member...then you should follow the conventions we have practiced in class.  We are using a POD class in this case because it
//simplifies the usage of the pixel object as well as keeps it's memory footprint tiny (as we will have MANY of these classes loaded
//into memory at a given time.)

#ifndef PIXEL_H
#define PIXEL_H

class pixel
{
public:
	unsigned char red;		//the red component
	unsigned char green;	//the green component
	unsigned char blue;		//the blue component
};

#endif


imageProcessing.cpp
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#include "image.h"
#include "pixel.h"
#include <iostream>
#include <string>
using namespace std;


void RotateClockWise(image *imageIn); //this function rotate the imageIn 90 degreee clockwise
void RotateAntiClockWise(image *imageIn); //this function rotate the imageIn 90 degree anticlockwise

int main()
{
	//testing image 1
	image* currImage=new image("testing1.jpg");
	currImage->createNewImage(600,700); // create a new (4 blocks with different color) image with input size
	currImage->saveImage("fourColor.jpg");

	//testing image 2
	currImage=new image("testing2.jpg");
	RotateClockWise(currImage);
	currImage->saveImage("test2RotateClock.jpg");

	//testing image 3
	currImage=new image("testing3.jpg");
	RotateAntiClockWise(currImage);
	currImage->saveImage("test3RotateAntiClock.jpg");

	//testing copy concstructor using image 4
	image a("testing4.jpg");
	image b=a;
	b.createNewImage(100,100);
	b.saveImage("testing4color.jpg");
	// a should remain the same, so testing4.jpg will not be changed. 

	system("pause");
	return 0;
}

 void RotateClockWise(image *imageIn)
 {
	//please provide the code for this function
}

 void RotateAntiClockWise(image *imageIn)
 {
	 //please provide code for this function
 }
Last edited on
kbw (9488)
Should be:
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	//provide the code for this function
	pixel **p = new pixel*[width];

	for (int j = 0; j < width; j++)
		p[j] = new pixel[height];
maninbluerobe (5)
still an access reading violation on the same line
kbw (9488)
You should be using standard containers for that.

My guess is you probably corrupted the heap earlier.
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