Question

So I had one large function that worked. Then I decided to modify it and now I am just printing out a black square. I am attaching my code to see if any one would understand what is happening. These three function where once large function:
Function 1

int
readpgm (pgm_type * header, char input[80], char output[80])
{
    FILE *instream;

    int size, read;
    instream = fopen (input, "rb");

    fileChecker (instream);

    fscanf (instream, "%2s%d%d%d", header->filetype, &header->width,
        &header->height, &header->maxgray);

    if (!header->filetype[0] == 'P' || !header->filetype[1] == '5') {
        fatal ("Incorrect Type");
    }

    size = header->width * header->height;

    header->p = malloc (size * sizeof (char));

    read = fread (header->p, 1, size, instream);
    if (read != size) {
        fatal ("Incorrect Size");
    }

    return size;
}

void
crop (pgm_type * header, char output[80])
{
    printf ("Height: %i, Width: %i, Total pixels: %i \n", header->height,
        header->width, header->height * header->width);

    int temp, y1, y2, x1, x2, wide, high;

    printf ("Please Enter x1 y1 x2 y2 \n");


    scanf ("%i %i %i %i", &x1, &y1, &x2, &y2);
    if (y1 > y2) {
        temp = y1;
        y1 = y2;
        y2 = temp;
    }
    if (x1 > x2) {
        temp = x1;
        x1 = x2;
        x2 = temp;
    }
    wide = x2 - x1 + 1;
    high = y2 - y1 + 1;

    printFile (wide, high, x1, x2, y1, y1, header, output);
}

void
printFile (int wide, int high, int x1, int x2, int y1, int y2,
       pgm_type * header, char output[80])
{
    FILE *outstream;

    outstream = fopen (output, "wb");

    fileChecker (outstream);

    fprintf (outstream, "%2s\n%i %i\n%i\n", header->filetype, wide, high,
         header->maxgray);

    pixel image[header->height][header->width];
    pixel *pix = malloc ((wide * high) * sizeof (char));

    int a = 0;

    for (int b = 0; b < header->height; ++b) {
        for (int c = 0; c < header->width; ++c) {
            image[b][c] = header->p[a];
            ++a;
        }
    }

    int k = 0;
    for (int i = y1; i <= y2; ++i) {
        for (int j = x1; j <= x2; ++j) {
            pix[k] = image[i][j];
            ++k;
        }
    }

    fwrite (pix, 1, (wide * high) * sizeof (pixel), outstream);
    free (pix);
    fclose (outstream);
}

The first two function are call in main.

Answer 1

This works for me.

//gcc c2.c -std=c99  -g -Wall -Wextra
#include <stdio.h>
#include <malloc.h>
#include <assert.h>

typedef struct pgm_type pgm_type;
struct pgm_type{
  char filetype[2];
  int width,height,maxgray;
  unsigned char*p;
};


int
readpgm (pgm_type * header, char*fn)
{
    FILE *instream;

    int size, read;
    instream = fopen (fn,"rb");

    assert(instream);

    fscanf (instream, "%2s%d%d%d", header->filetype, &header->width,
        &header->height, &header->maxgray);
    printf("%2s %d %d %d\n",header->filetype,header->width,
       header->height,header->maxgray);

    if (!header->filetype[0] == 'P' || !header->filetype[1] == '5') {
      printf ("Incorrect Type");
    }

    size = header->width * header->height;

    header->p = malloc (size * sizeof (char));

    read = fread (header->p, 1, size, instream);
    if (read != size) {
      printf ("Incorrect Size");
    }

    return size;
}

void
printFile (int x1, int x2, int y1, int y2,pgm_type * header, char*fn)
{
    FILE *outstream;
    int wide=x2-x1+1,high=y2-y1+1;
    printf("cropping to %dx%d\n",wide,high);
    outstream = fopen (fn, "wb");

    assert (outstream);

    fprintf (outstream, "%2s\n%i %i\n%i\n", header->filetype, wide, high,
         header->maxgray);

    unsigned char image[header->height][header->width];
    unsigned char *pix = malloc ((wide * high) * sizeof (char));

    int a = 0;

    for (int b = 0; b < header->height; ++b) {
        for (int c = 0; c < header->width; ++c) {
            image[b][c] = header->p[a];
            ++a;
        }
    }

    int k = 0;
    for (int j = y1; j <= y2; ++j) {
        for (int i = x1; i <= x2; ++i) {
            pix[k] = image[j][i];
            ++k;
        }
    }

    fwrite (pix, wide,high, outstream);
    free (pix);
    fclose (outstream);
}


int
main()
{
  pgm_type h;
  readpgm(&h,"lena.pgm");
  printFile(64,129,32,230,&h,"o2.pgm");
  return 0;
}