Pset4 resize strange resized image and does not resize after some value

Question

I am stuck since I have no idea what is wrong with my code. I believe my resizing code is correct. I think I'm not changing the headers correctly, which is giving me this image:

Also, i think it doesn't resize after i give a resize value of bigger than 20. It outputs Incorrect file type, which makes me even more suspectible of the file headers.

The CS50's peek line:

./resize 4 small.bmp student.bmp
~cs50/pset4/resize 4 small.bmp staff.bmp
~cs50/pset4/peek student.bmp staff.bmp

outputs all correct (green).

The other problem is that sometimes it resizes sometimes it keeps the same size even after inputting different value.

This code is a mess, and I've been stuck on resize for well over a week now. I've looked through some help here but couldn't come up with a solution. Any help is aprreciated.

    /**
 * Copies a BMP piece by piece, just because.
 */

#include <stdio.h>
#include <stdlib.h>
#include <cs50.h>

#include "bmp.h"

int main(int argc, char *argv[])
{
    // ensure proper usage
    if (argc != 4)
    {
        fprintf(stderr, "Usage: ./copy n infile outfile\n");
        return 1;
    }

    // remember filenames
    int resize = atoi(argv[1]);
    char *infile = argv[2];
    char *outfile = argv[3];

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

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

    // 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;
    }

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

    // add another variable for headers
    BITMAPINFOHEADER bi_out = bi;
    BITMAPFILEHEADER bf_out = bf;

    // change members' sizes before writing
    bi_out.biWidth *= resize;

    // copy padding for scanlines
    int paddingChanged = (4 - (bi_out.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    bi_out.biHeight *= resize;
    bi_out.biSizeImage = ((sizeof(RGBTRIPLE) * bi_out.biWidth) + paddingChanged) * abs(bi_out.biHeight);
    bf_out.bfSize = bi_out.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

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

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

    // (recopy method) (Zamyla's pseudocode) FOR EACH ROW
    // iterate over infile's scanlines
    for (int i = 0, y = abs(bi_out.biHeight); i < y; i++)
    {
        // FOR n-1 TIMES
        // write same lines n times
        for (int m = 0, x = resize - 1; m < x; m++)
        {
            // WRITE PIXELS TO OUTFILE
            // iterate over pixels in scanline
            for (int j = 0; j < bi_out.biWidth; j++)
            {
                // temporary storage
                RGBTRIPLE triple;

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

                // write triple n times
                for (int k = 0; k < resize; k++)
                {
                    // write RGB triple to outfile
                    fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
                }
            }

            // WRITE PADDING TO OUTFILE
            for (int k = 0; k < paddingChanged; k++)
            {
                fputc(0x00, outptr);
            }

            // SEND INFILE COURSOR BACK
            fseek(inptr, 0, SEEK_SET);
        }

        // ADD PIXELS TO OUTFILE
        for (int j = 0; j < bi_out.biWidth; j++)
        {
            // temporary storage
            RGBTRIPLE triple;

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

            // write triple n times
            for (int k = 0; k < resize; k++)
            {
                // write RGB triple to outfile
                fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
            }
        }

        // ADD PADDING TO OUTFILE
        for (int k = 0; k < paddingChanged; k++)
        {
            fputc(0x00, outptr);
        }

        // SKIP OVER INFILE PADDING
        fseek(inptr, padding, SEEK_CUR);
    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}

UPDATE: The problems were:

1. I was using too many iterations on the for() loops. I changed bi_out.biWidth and bi_out.biHeight to bi.biWidth and bi.biHeight inside these loops.
2. My fseek() line was incorrect. I changed it to fseek(inptr, -(long)bi.biWidth * (long)sizeof(RGBTRIPLE), SEEK_CUR); and it is finally working now.

Answer 1

In your for loops, use bi.biHeight, not bi_out.biHeight. Together with your nested loops, you'll get to bi_out.biHeight lines written in total.

Same for width, which has its own two nested loops.

Instead of resetting to start of the file

fseek(inptr, 0, SEEK_SET);

do like

fseek(inptr, -bi.biWidth * sizeof(RGBTRIPLE), SEEK_CUR);

to reset to the start of the line.

An alternative could be to read the line, saving it to an array, and writing it resize times.