// Resize a BMP file

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

#include "bmp.h"

int main(int argc, char *argv[]) { // ensure proper usage if (argc != 4) { fprintf(stderr, "Usage: %s n infile outfile\n", argv[0]); return 1; }

// remember filenames
int n = atoi(argv[1]);
if ( n < 0 )
{
    fprintf(stderr, "Usage: %s n infile outfile\n", argv[0]);
    return 2;
}

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 3;
}

// open output file
FILE *outptr = fopen(outfile, "w");
if (outptr == NULL)
{
    fclose(inptr);
    fprintf(stderr, "Could not create %s.\n", outfile);
    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 5;
}
// determine padding for scanlines
int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
int new_padding = (4 - (n * bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

// Update BITMAPINFOHEADER
BITMAPINFOHEADER new_bi;
new_bi.biWidth = n * bi.biWidth;
new_bi.biHeight = n * bi.biHeight;
new_bi.biSizeImage = ((sizeof(RGBTRIPLE) * new_bi.biWidth) + new_padding) + abs(new_bi.biHeight);

// Update BITMAPFILEHEADER
BITMAPFILEHEADER new_bf;
new_bf.bfSize = new_bi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

//printf("%lu\n",sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER));



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

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

// iterate over infile's scanlines
for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
{
    for (int l = 0; l < n - 1 ; l++)
    {
        // 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);

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

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

        // send infile cursor back
        fseek(inptr, padding, SEEK_CUR);
    }

    // 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);

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

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

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

}

// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// success
return 0;

}

Code:

// Resize a BMP file

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

#include "bmp.h"

int main(int argc, char *argv[])
{
    // ensure proper usage
    if (argc != 4)
    {
        fprintf(stderr, "Usage: %s n infile outfile\n", argv[0]);
        return 1;
    }

    // remember filenames
    int n = atoi(argv[1]);
    if ( n < 0 )
    {
        fprintf(stderr, "Usage: %s n infile outfile\n", argv[0]);
        return 2;
    }

    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 3;
    }

    // open output file
    FILE *outptr = fopen(outfile, "w");
    if (outptr == NULL)
    {
        fclose(inptr);
        fprintf(stderr, "Could not create %s.\n", outfile);
        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 5;
    }
    // determine padding for scanlines
    int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
    int new_padding = (4 - (n * bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

    // Update BITMAPINFOHEADER
    BITMAPINFOHEADER new_bi;
    new_bi.biWidth = n * bi.biWidth;
    new_bi.biHeight = n * bi.biHeight;
    new_bi.biSizeImage = ((sizeof(RGBTRIPLE) * new_bi.biWidth) + new_padding) + abs(new_bi.biHeight);

    // Update BITMAPFILEHEADER
    BITMAPFILEHEADER new_bf;
    new_bf.bfSize = new_bi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

    //printf("%lu\n",sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER));



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

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

    // iterate over infile's scanlines
    for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
    {
        for (int l = 0; l < n - 1 ; l++)
        {
            // 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);

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

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

            // send infile cursor back
            fseek(inptr, padding, SEEK_CUR);
        }

        // 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);

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

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

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

    }

    // close infile
    fclose(inptr);

    // close outfile
    fclose(outptr);

    // success
    return 0;
}