Pset4 resize (less) Invalid file format

Question

This pset has been super hard for me. I am trying to resize horizontally before I tackle vertical and I am able to compile and run the program but when I go to open the output file I get the error message "Invalid or Unsupported Image Format."

I've backed out of my changes from copy.c and the problem seems to be when I change the fwrite from &bf to &bfresize and &bi to &biresize. I see several others have had the same problem but my code already includes one of the recommended fixes in one of them and doesn't include what I think was problematic in the others. I've read through them all and I still don't see it.

I was able to get the image to open yesterday and I can't remember what I changed since then that might be causing this problem. I've moved some things around, did I accidentally delete a line of code? I'm sure it's something stupid but I've looked at it over and over and I just don't see it. Help would be much appreciated.

// Copies a BMP file

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

#include "bmp.h"

int main(int argc, char *argv[])
{
// ensure proper usage
if (argc != 4)
{
    fprintf(stderr, "Usage: resize factor small large\n");
    return 1;
}

// remember filenames
char *small = argv[2];
char *larger = argv[3];
int n = atoi(argv[1]);

// open input file
FILE *inptr = fopen(small, "r");
if (inptr == NULL)
{
    fprintf(stderr, "Could not open %s.\n", small);
    return 2;
}

// open output file
FILE *outptr = fopen(larger, "w");
if (outptr == NULL)
{
    fclose(inptr);
    fprintf(stderr, "Could not create %s.\n", larger);
    return 3;
}

//Ensure argv[1] is a number between 1 and 100
if (n < 0 || n > 100)
{
    fprintf(stderr, "Choose a resize factor between 1 and 100.\n");
    return 4;
}

// read infile's BITMAPFILEHEADER
BITMAPFILEHEADER bf;
fread(&bf, sizeof(BITMAPFILEHEADER), 1, inptr);

// read infile's BITMAPINFOHEADER
BITMAPINFOHEADER bi;
fread(&bi, sizeof(BITMAPINFOHEADER), 1, inptr);

// ensure infile is (likely) a 24-bit uncompressed BMP 4.0
if (bf.bfType != 0x4d42 || bf.bfOffBits != 54 || bi.biSize != 40 ||
    bi.biBitCount != 24 || bi.biCompression != 0)
{
    fclose(outptr);
    fclose(inptr);
    fprintf(stderr, "Unsupported file format.\n");
    return 4;
}

BITMAPFILEHEADER bfresize = bf;
BITMAPINFOHEADER biresize = bi;

biresize.biWidth = bi.biWidth * n;
biresize.biHeight = bi.biHeight * n;

// determine padding for scanlines
int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
int paddingresize = (4 - (biresize.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

biresize.biSizeImage = ((sizeof(RGBTRIPLE) * biresize.biWidth) + paddingresize) * abs(biresize.biHeight);
bfresize.bfSize = biresize.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

// write outfile's BITMAPFILEHEADER
fwrite(&bfresize, sizeof(BITMAPFILEHEADER), 1, outptr);

// write outfile's BITMAPINFOHEADER
fwrite(&biresize, sizeof(BITMAPINFOHEADER), 1, outptr);

// iterate over infile's scanlines
for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
{
    // iterate over pixels in scanline
    for (int j = 0; j < bi.biWidth; j++)
    {

        // temporary storage
        RGBTRIPLE triple;

        // read RGB triple from infile
        fread(&triple, sizeof(RGBTRIPLE), 1, inptr);

        for (int l = 0; l < n; l++)

        // write RGB triple to outfile
        fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);

    }

    // skip over padding, if any
    fseek(inptr, padding, SEEK_CUR);

    // then add it back (to demonstrate how)
    for (int k = 0; k < paddingresize; k++)
    {
        fputc(0x00, outptr);
    }
}

// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// success
return 0;
}

Answer 1

Went back to the walkthrough and went through my code line by line with Zamyla. I think I see it (I was right, it is something really really obvious and called out specifically in the walkthrough). It's working on smiley (stretches smiley out). Doesn't seem to stretch small so much as force the pixels to run into the next set of pixels (I now have red and blue pixels instead of just green and white) but I am back to being hopeful.