Resize

#include <stdio.h>#include <stdlib.h>
#include "bmp.h"
int main(int argc, char *argv[]){    // Grab enlargement factor    int n = atoi(argv[3]);
    // ensure proper usage    if (argc != 4 || n > 100)    {        fprintf(stderr, "Usage: ./resize infile outfile enlarge_factor(0-100)\n");        return 1;    }
    // remember filenames    char *infile = argv[1];    char *outfile = argv[2];
    // 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;    }
    // grabbing the padding calculation for the original read file    int paddingRead =  (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;    int biWidthRead = bi.biWidth;
    // resizing file header for the new image size.    bi.biWidth = bi.biWidth * n;    bi.biHeight = bi.biHeight * n;
    // write outfile's BITMAPFILEHEADER    fwrite(&bf, sizeof(BITMAPFILEHEADER), 1, outptr);
    // write outfile's BITMAPINFOHEADER    fwrite(&bi, sizeof(BITMAPINFOHEADER), 1, outptr);
    // determine padding for scanlines    int padding =  (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    // 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 < biWidthRead; j++)        {            // temporary storage            RGBTRIPLE triple;
            // read RGB triple from infile            fread(&triple, sizeof(RGBTRIPLE), 1, inptr);
            // print out n pixels to stretch horizontally            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, paddingRead, SEEK_CUR);
        // then add it back (to demonstrate how)        for (int k = 0; k < padding; k++)        {            fputc(0x00, outptr);        }
        // seeking back to print n scanlines, stratching vertically        if(i % n != n - 1)        {            fseek(inptr, - (biWidthRead * sizeof(RGBTRIPLE) + paddingRead), SEEK_CUR);        }    }
    // close infile    fclose(inptr);
    // close outfile    fclose(outptr);
    // success    return 0;}