Is this right?

**klee87** · 06-03-2013

NOTE: I had a previous thread about this, but since that post, I've attempted to come up with some solutions.

Just to show you, this is the place in my program where I got the variables for width and height from the input image file:

Code:

void read_header(FILE *new)
{
   int max_color;
   char P[10];


   fgets(P, 10, new);
   fscanf(new, "%d %d", &width, &height);
   fscanf(new, "%d", &max_color);
}

PART 1:

What I need to do is print out an error if the file size exceeds the 500 by 500 measurements (defined at the top as max_width and height).

PART 2: The other part is that I have to read the pixel information from the input file and store it into a 2d array. Each pixel has 3 values for red, green, and blue, but I'm not sure if this matters.

My attempt at both solutions:

Part 1:

Code:

void check_file_size /*Don't know what to put because width and height are global variables*/
{
   if (width > 500 && height > 500)
   {
      perror("Error: File size too big.\n");
   }
}

Part 2:

Code:

void store_into_array(FILE *input)
{
   int array[max_width][max_height];


   for (x = 0; x < width; x++)
   {
      for (y = height; y >=0; y--)
      {
         fscanf(input, "%d", &array[x][y]);
      }
   }
}

**laserlight** · 06-03-2013

Why are width and height global variables?

**klee87** · 06-03-2013

Because I had to use it in two separate helper functions, the one where I check the file size and the one where I stored the values into the 2d array.

**laserlight** · 06-03-2013

Originally Posted by klee87

Because I had to use it in two separate helper functions, the one where I check the file size and the one where I stored the values into the 2d array.

Poor excuse. You should make them local variables and pass them to the helper functions instead.

**migf1** · 06-04-2013

Given the info provided by this and the other post, along with the info provided by this link, here is a possible approach, regarding PART1 of your question...

Code:

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define MAGIC		"P3"	/* http://netpbm.sourceforge.net/doc/ppm.html */
#define MAX_H		500
#define MAX_W		500

typedef struct {
	char magic[3];
	int width, height;
	int maxColor;
	int pix[MAX_H][MAX_W];
}Ppm;

/* --------------------------------------------------- */
int ppm_has_valid_header( Ppm *image, int maxWidth, int maxHeight )
{
	if ( !image || maxWidth < 1 || maxHeight < 1 )
		return 0;	/* false */

	return	0 == strcmp(MAGIC, image->magic)
		&& image->width  > 0 && image->width  < 1 + maxWidth
		&& image->height > 0 && image->height < 1 + maxHeight
		;
}
/* --------------------------------------------------- */
int main( void )
{
	Ppm img;
	int temp;

	FILE *fp = fopen( "_ppm.txt", "r" );
	if ( !fp )
		goto failed_exit;

	/* start fresh */
	memset( &img, 0, sizeof(Ppm) );

	/* PART1 : read header data */
	temp = fscanf( fp, "%2s %d %d %d", img.magic, &img.width, &img.height, &img.maxColor );
	if ( 4 != temp
	|| !ppm_has_valid_header(&img, MAX_W, MAX_H)
	){
		fputs( "*** invalid or too big image, aborting...\n", stderr );
		goto failed_exit;
	}

	printf( "%s\t(magic)\n%d %d\t(width height)\n%d\t(max color value)\n",
		img.magic, img.width, img.height, img.maxColor
		);

	/* PART2: read pixel data into img.pix
	...
	*/

	fclose( fp );

	return 0;

failed_exit:
	if (fp)
		fclose(fp);
	return 1;

}

PART2 is more tricky. I would most probably read all three pixel samples using just one scanf(), because the file is expected to be well-formatted.

Something like the following...

Code:

	hasmore = 1; /* true */
	for (i=0; hasmore && i < img.height; i++)
	{
		for (j=0; j < 3 * img.width; j+=3) 
		{
			temp = fscanf(	fp,
					"%d %d %d",
					&img.pix[i][j],		/* red */
					&img.pix[i][j+1],	/* green */
					&img.pix[i][j+2]	/* blue */
					);
			...
		}
	}

with temp and hasmore used for further validating the process, informing the user and breaking out of the nested loop as needed.

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