PSET4: Resize (less comfortable) - confusion regarding segfault and horizontal resizing

Question

Here is what I've got for PSET4: Resize so far. I get a segfault with proper usage of the program (i.e ./resize n infile outfile), and I have no clue where it's coming from. Furthermore, is my approach to horizontal resizing correct? When writing the RGBTRIPLE "triple" to the new scanline, I simply write the triple "n" times (I used "scale" as the variable for "n") by passing in "scale" as the in the fwrite() function.

// Copies a BMP file

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

#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[1];
    char *outfile = argv[2];

    // if second element in argv[] array is not a number, return 1 to main()
    if (!isdigit(argv[1]))
    {
        return 1;
    }

    int scale = atoi(argv[1]);

[EDIT: unrelated code removed for Honor Code compliance.]

Answer 1

There are a couple of issues.

First, the arg numbers used for the filenames are incorrect. I'll let you figure out why.

Second, the seg fault, is being caused here:

    if (!isdigit(argv[1]))

argv[1] is a string. isdigit takes a single char. The code is trying to shove a string down isdigit's throat and it chokes, generating the seg fault. It's the wrong approach anyways. This would only check that one char is a digit, not the whole string.

Better to convert the string to an int, as you did later when you assigned the value to scale, and test that it is within the required range from the program specification.

As for whether this is the correct approach, well, why don't you test it after making the fixes. ;-)

When you move from scale=1 to scale=2, you'll also have to make some corrections in the headers. Happy coding! ;-)

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