pset3 resize (less) - double free or corruption (fasttop)

Question

the code is working with small.bmp, but not with large.bmp and i can't understand why. Even resizing smiley.bmp, when n is too big it's not working. Here's the code:

// Copies a BMP file

include

include

include "bmp.h"

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

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

//ensure n <= 100
if (n < 1 || n > 100)
{
    fprintf(stderr, "Usage: ./resize n infile outfile\n");
    return 6;
}

// 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;
}

//determine oldpadding
int oldpadding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;

//save width and height for later usage
int width = bi.biWidth;
int height = abs(bi.biHeight);

//update file headers and padding
bi.biWidth *= n;
bi.biHeight *= n;
int padding = (4 - (bi.biWidth * sizeof(RGBTRIPLE)) % 4) % 4;
bi.biSizeImage = ((sizeof(RGBTRIPLE) * bi.biWidth) + padding) * 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 to store pixels for resizing
RGBTRIPLE *pixels = malloc(sizeof(RGBTRIPLE) * bi.biWidth);

// iterate over infile's scanlines
for (int i = 0, p; i < height; i++)
{
    //set p = 0 to iterate over the array where pixels are stored
    p = 0;

    // iterate over pixels in scanline
    for (int j = 0; j < width; j++)
    {
        // temporary storage
        RGBTRIPLE triple;

        // read RGB triple from infile
        fread(&triple, sizeof(RGBTRIPLE), 1, inptr);

        // write RGB triple into the array n times
        for (int k = 0; k < n; k++)
        {
            pixels[p] = triple;
            p++;
        }
    }

    // write array to outfile n times and add padding for each line
    for (int a = 0; a < n; a++)
    {
        fwrite(pixels, sizeof(RGBTRIPLE) * bi.biWidth, 1, outptr);
        for (int d = 0; d < padding; d++)
        {
            fputc(0x00, outptr);
        }
    }

    //free memory of array
    free(pixels);

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

// close infile
fclose(inptr);

// close outfile
fclose(outptr);

// success
return 0;

}

Answer 1

Move free(pixels) out of your loop.

You could also use RGBTRIPLE pixels[bi.biWidth]; instead of malloc, removing the need for free.