Could someone please tell me where I'm going wrong here in resize-less(pset4)?

Question

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

#include <string.h>

#include "bmp.h"

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

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

//ensure n less than 100

if(n > 100 || n < 1)
{
    fprintf(stderr, "n shouldnt be more than 100");
    return 1;
}

// 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;
}


BITMAPINFOHEADER bi_out;
bi_out=bi;

bi_out.biHeight *= n;
bi_out.biWidth *= n;

// determine padding for scanlines of ofile
int padding2 = (4 - ((bi_out.biWidth) * sizeof(RGBTRIPLE)) % 4) % 4;
int padding  = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

bi_out.biSizeImage = ((sizeof(RGBTRIPLE) * bi_out.biWidth) + padding2) * abs(bi_out.biHeight);
bf.bfSize = bi_out.biSizeImage + 54; // sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);





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

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




// iterate over infile's scanlines
for (int i = 0; i < abs(bi_out.biHeight); i++)
{
    // 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);

        for(int k = 0; k < n; ++k)
        {
            fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
        }

    }


    for (int k = 0; k < padding2; k++)
    {
        fputc(0x00, outptr);
    }

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

}


// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// success
return 0;

}

Answer 1

There are two major issue. First, the code is using biWidth and biHeight for the output file to control reading from the input file.

Second, there's no actual code to handle vertical scaling.

Perhaps a review of the walkthroughs is in order?

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