Imagine we're building a utility for joining MP3 files. We want the user to supply the file names as a list of command line arguments. We also want to support an --out/-o option so the user can specify an output filename and a --quiet/-q flag for turning down the program's verbosity.

First we need to create an ArgParser instance:

#include "args.h"

ArgParser* parser = ap_new_parser();
ap_set_helptext(parser, "Usage: mp3cat...");
ap_set_version(parser, "1.0");

Supplying a helptext string for the parser activates an automatic --help/-h flag; similarly, supplying a version string activates an automatic --version/-v flag.

Now we can register our options and flags:

ap_add_str_opt(parser, "out o", "default.mp3");
ap_add_flag(parser, "quiet q");

That's it, we're done specifying our interface. Now we can parse the program's command line arguments, passing in argc and argv as supplied to main():

ap_parse(parser, argc, argv);

This will exit with a suitable error message for the user if anything goes wrong. Now we can check if the --quiet flag was found:

if (ap_found(parser, "quiet")) {
    do_stuff();
}

And determine our output filepath:

char* path = ap_get_str_value(parser, "out");

The input filenames will be collected by the parser into a list of positional arguments which we can access in various ways, e.g

for (int i = 0; i < ap_count_args(parser); i++) {
    char* filename = ap_get_arg_at_index(parser, i);
    do_stuff();
}

When we're finished using it, we can free up the parser's memory:

ap_free(parser);