How to use Printf like format string with argv

Question

I'm trying to add support to my program for something that would allow me to enter /Input/Images/%03d.png /Output/Images/%03d.blah, but I'm not sure how to do that?

I've googled around for every combination of format string, printf, and argv that I can think of.

I want to e able to load everything before the %03d as a constant, and loop over %03d to select multiple different input files, in order, to read them in. so it would be /Input/Images/000.png, then /Input/Images/001.png all the way to /Input/Images/999.png.

tl;dr I want to handle a sequence of files, but I don't know how to do that.

Sounds like a perfect recipe for all kinds of format string attacks. — Eugene Sh., Aug 13 '15 at 17:31
Are you trying to pattern-match on file names/paths, or do you know what value you want to substitute into `%03d`? — Matt Olson, Aug 13 '15 at 17:34
What have you tried? As @EugeneSh. wrote, doing that would open up to attack, since the `argv` string would have to be passed to `printf` or `sprintf` as the first argument. Better to split your program arguments into `source` and `dest` then you can build the full filenames without fear of damage. — Weather Vane, Aug 13 '15 at 17:44
Please be more specific, what exactly should your program do ? You write you want to enter `/Input/Images/%03d.png /Output/Images/%03d.blah` but then what ? — Jabberwocky, Aug 13 '15 at 17:49
It would be a string of digits, I was thinking that like 0 would mean leading zeros, 3, 4, 5, whatever would be the number of digits, and d would be for decimal like other programs use. I want to be able to take in the path of the file, and loop over the digits of the file name in order to select a group of files. lets say there are ten files all named Frame_00x.png, I want to be able to take the path, and everything before the x in the file name as a constant, and loop over x up to 10 times, so I can read in all of those files. — MarcusJ, Aug 13 '15 at 18:25
Then pass the base number of the file set and the number of files you want to process, and build the loop and the filenames from those. — Weather Vane, Aug 13 '15 at 18:39

score 1 · Accepted Answer · answered Aug 13 '15 at 18:58

You could do it like this. The solution leaves much to be desired in string size checking, but the basis is this.

You enter the paths and the file number base and and the number of files in the batch you want to process.

#include <stdio.h>

int main (int argc, char *argv[])
{
    unsigned basenum, numfiles, i;
    char inname[1000], outname[1000];

    if (argc < 5)
        return 1;
    sscanf(argv[3], "%u", &basenum);
    sscanf(argv[4], "%u", &numfiles);
    for (i=0; i<numfiles; i++) {
        sprintf (inname, "%s/%03u.png", argv[1], basenum + i);
        sprintf (outname, "%s/%03u.blah", argv[2], basenum + i);
        //convertimg (inname, outname);
        printf ("Processed %s to %s\n", inname, outname);
    }
return 0;
}

Program input

test aaa dest/bbbb 100 10

Program output

Processed aaa/100.png to dest/bbbb/100.blah
Processed aaa/101.png to dest/bbbb/101.blah
Processed aaa/102.png to dest/bbbb/102.blah
Processed aaa/103.png to dest/bbbb/103.blah
Processed aaa/104.png to dest/bbbb/104.blah
Processed aaa/105.png to dest/bbbb/105.blah
Processed aaa/106.png to dest/bbbb/106.blah
Processed aaa/107.png to dest/bbbb/107.blah
Processed aaa/108.png to dest/bbbb/108.blah
Processed aaa/109.png to dest/bbbb/109.blah

How to use Printf like format string with argv

1 Answers1