Resize less comfortable; still stuck; cannot understand f(seek)

Question

I thought I got it, but still stuck. any help appreciated

/** * resizes bmp piece by piece */

include

include

include "bmp.h"

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

// make sure resize facotr is valid
int factor = atoi(argv[2]);
if (factor < 0 || factor >100)
{
    printf("factor must be positive integer less or equal to 100.\n");
    return 2;
}




// remember filenames
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 4;
}

// construct bitmap headers for the outfile
BITMAPFILEHEADER out_bf;
BITMAPINFOHEADER out_bi;

out_bf = bf;
out_bi = bi;

out_bi.biWidth = bi.biWidth*factor;
out_bi.biHeight = bi.biHeight*factor;

// work out padding for scanlines
int in_padding = (4 - (bi.biWidth*sizeof(RGBTRIPLE))%4)%4;
int out_padding = (4 - (out_bi.biWidth*sizeof(RGBTRIPLE))%4)%4;

// work out change of image size
out_bi.biSizeImage = ((sizeof(RGBTRIPLE)*out_bi.biWidth) + out_padding)*abs(out_bi.biHeight);

//work out change of file size
out_bf.bfSize = out_bi.biSizeImage + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);



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

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


// iterate over infile's scanlines
for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight; i++)
{
    // ensure each line is written factor times
    for (int n = 0; n < factor; n++)
    {
        // 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);

            // ensure repeated factor times
            for (int m = 0; m < factor; m++)
            {
            // write RGB triple to outfile
            fwrite(&triple, sizeof(RGBTRIPLE), 1, outptr);
            }
        }
        // skip over padding, if any
        fseek(inptr,in_padding, SEEK_CUR);

        // write padding to outffile
        for (int k = 0; k < out_padding; k++)
        {
            fputc(0x00, outptr);
        }
        // return cursor
        fseek(inptr, -(bi.biWidth*sizeof(RGBTRIPLE)+ in_padding), SEEK_CUR);
    }
    //return cursor again I dont know why
    fseek(inptr, (bi.biWidth*sizeof(RGBTRIPLE)+ in_padding), SEEK_CUR);
}
// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// success
return 0;

}

Answer 1

You have to check your command line arguments. You take the third argument as the resize factor and as the infile name.