segmentation fault only when I use certain resolutions

This is a discussion on segmentation fault only when I use certain resolutions within the C Programming forums, part of the General Programming Boards category; Hey! I am still writing my image manipulation program to learn more about pointers. I thought I was doing well ...

  1. #1
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    Aug 2007
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    segmentation fault only when I use certain resolutions

    Hey! I am still writing my image manipulation program to learn more about pointers. I thought I was doing well this time, but yesterday I realized that it gives me "Segmentation fault" when I use images with certain resolutions.

    Code:
    #include <stdio.h>
    #include <stdarg.h>
    #include <stdlib.h>
    #include <string.h>
    #include <math.h>
    
    typedef enum {NO, YES} Bool;
    
    typedef struct GS8Pixel {
    	int level;
    } GS8Pixel;
    typedef struct GS8Image {
    	int width, height;
    	GS8Pixel *data;
    } GS8Image;
    
    void createGS8Image(GS8Image **image, int width, int height);
    void freeGS8Image(GS8Image **image);
    GS8Pixel getPixelOfGS8Image(GS8Image *image, int x, int y);
    void setPixelOfGS8Image(GS8Image *image, int x, int y, int level);
    int getP3StringSizeOfGS8Image(GS8Image *image);
    void GS8ImageToP3String(char *str, GS8Image *image);
    Bool GS8ImageToP3File(char *file_path, GS8Image *image);
    void scaleGS8ImageWithNearestNeighbourInterpolation(GS8Image **new_image, GS8Image *old_image, float scale);
    
    void createGS8Image(GS8Image **image, int width, int height)
    {
    	int i;
    	*image = malloc(sizeof(GS8Image));
    	(*image)->data = malloc(sizeof(GS8Pixel)*width*height);
    //	if ((*image)->data == NULL) {
    //		fprintf(stderr, "out of memory!\n");
    //	}
    	for(i = 0; i < width*height; ++i)
    	{
    		((*image)->data)[i].level = 0;
    	}
    	(*image)->width = width;
    	(*image)->height = height;
    }
    void freeGS8Image(GS8Image **image)
    {
    	free((*image)->data);
    	free((*image));
    	*image = NULL;
    }
    GS8Pixel getPixelOfGS8Image(GS8Image *image, int x, int y) 
    {
    	return image->data[y*image->width+x];
    }
    void setPixelOfGS8Image(GS8Image *image, int x, int y, int level)
    {
    	image->data[y*image->width+x].level = level;
    }
    void scaleGS8ImageWithNearestNeighbourInterpolation(GS8Image **new_image, GS8Image *old_image, float scale) 
    {
    	int new_image_width, new_image_height, x, y, tmp_x, tmp_y;
    	new_image_width = (int) (scale * old_image->width);
    	new_image_height = (int) (scale * old_image->height);
    	createGS8Image(new_image, new_image_width, new_image_height);
    	for(y = 0; y < new_image_height; ++y)
    	{
    		for(x = 0; x < new_image_width; ++x)
    		{
    			tmp_x = (int) (x / scale + 0.5);
    			tmp_y = (int) (y / scale + 0.5);
    			getPixelOfGS8Image(*new_image, x, y);
    		}
    	}
    }
    
    Bool GS8ImageToP3File(char *file_path, GS8Image *image)
    {
    	FILE *fp;
    	char str[getP3StringSizeOfGS8Image(image)];
    	GS8ImageToP3String(str, image);
    	if((fp = fopen(file_path, "w"))==NULL) {
    		printf("unable to open file");
    		return NO;
    	}
    	fputs(str, fp);
    	fclose(fp);
    	return YES;
    }
    void GS8ImageToP3String(char *str, GS8Image *image)
    {
    	int i, tmp_level;
    	char tmp[70], *str_end;
    	strcpy(str, "P3\n");
    	sprintf(tmp, "&#37;d %d\n", image->width, image->height);
    	strcat(str, tmp);
    	strcat(str, "255\n");
    	str_end = str + strlen(str);
    	for(i = 0; i < image->width*image->height; ++i)
    	{
    		tmp_level = (image->data)[i].level;
    		sprintf(tmp, "%3d %3d %3d  ", tmp_level, tmp_level, tmp_level);
    		strcpy(str_end, tmp);
    		str_end += 13;
    		if ( i%10 ==9 ) {
    			strcpy(str_end, "\n");
    			str_end += 1;
    		}
    	}
    }
    int getP3StringSizeOfGS8Image(GS8Image *image)
    {
    	char tmp[70];
    	sprintf(tmp, "%d %d\n", image->width, image->height);
    	return 1 + strlen(tmp) + 3 + 4 + 13*image->width*image->width + (image->width*image->width/10);
    }
    
    
    int main (int argc, char const *argv[])
    {
    	GS8Image *a, *b, *c;
    	
    	createGS8Image(&a, 10, 10);
    	GS8ImageToP3File("test.ppm", a);
    	printf("10x10 done.\n");
    	
    	createGS8Image(&b, 1, 1);
    	GS8ImageToP3File("test.ppm", b);
    	printf("1x1 done.\n");
    	
    	createGS8Image(&c, 1, 10);
    	GS8ImageToP3File("test.ppm", c);
    	printf("1x10 done.\n");
    	return 0;
    }
    Resolutions that work -> 1x1, 10x10, 512x512
    Resolutions that don't work -> 1x10, 9x10, 1024x1024

    I don't get why I get segmentation faults. Can someone teach me?
    I've confirmed that the segmentation fault occurs when I access the array element
    (image->data)[i]
    the i when it happens changes according to the resolution.
    Last edited by kkjj; 08-27-2007 at 04:20 AM. Reason: Colored code

  2. #2
    Cogito Ergo Sum
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    Don't know anything about this, but colour the sections you think are the faulty areas for easier reading

  3. #3
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    thanks JFonseka! I've colored my code

  4. #4
    Cogito Ergo Sum
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    With my very limited knowledge, all I can think of is that you haven't allocated enough space for higher resolutions to be handled, hence why it's seg faulting.

  5. #5
    and the hat of wrongness Salem's Avatar
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    I find the colours unreadable - moving on...
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
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