Resize v2

// Resizes a BMP file

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "bmp.h"

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

    float n = atof(argv[1]);
    char *infile = argv[2];
    char *outfile = argv[3];

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

    // open output file
    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;
    }

    // dimensions of original picture
    int originalWidth = bi.biWidth;
    int originalHeight = abs(bi.biHeight);
    int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    // dimensions of resized picture
    bi.biWidth = floor(n*bi.biWidth);
    bi.biHeight = floor(n*bi.biHeight);
    int paddingResize = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    bi.biSizeImage = ((sizeof(RGBTRIPLE)*bi.biWidth)+paddingResize)*abs(bi.biHeight);
    bf.bfSize = bi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

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

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

    // create array that stores pixels of original picture
    RGBTRIPLE pixels[originalHeight][originalWidth];

    // iterate over infile's scanlines
    for (int row = 0; row < originalHeight; row++)
    {
        // iterate over pixels in scanline
        for (int col = 0; col < originalWidth; col++)
        {
            //put pixel in array
            fread(&pixels[row][col], sizeof(RGBTRIPLE), 1, inptr);
        }
        fseek(inptr, padding, SEEK_CUR);
    }

    // writes resized image to outfile
    for(int row = 0; row < originalHeight; row++)
    {
        for(int resizeVertical = 0; resizeVertical < n; resizeVertical++)
        {
            for(int col = 0; col < originalWidth; col++)
            {
                for(int resizeH = 0; resizeH < n; resizeH++)
                {
                    fwrite(&pixels[row][col], sizeof(RGBTRIPLE), 1, outptr);
                }
            }
            for (int k = 0; k < paddingResize; k++)
            {
                fputc(0x00, outptr);
            }
        }
    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}