GNU argp "too few arguments" - c++

Question

My program is supposed to take two required arguments, and three optional arguments, like follows
ATE <input file> <output file> [--threads] [--bass] [--treble]
(note, I haven't figured out how to take <required> arguments yet, so input and output file is defined in the code as -i input_file and -o output_file)
I'm using the GNU library argp to parse the command line arguments, my file is based off the third example.
I run my program using the following command
$ ./ATE -i input_file.pcm -o output_file.pcm
Too few arguments!
Usage: ATE [OPTION...]
-p AMOUNT_OF_THREADS -b BASS_INTENSITY -t TREBLE_INTENSITY
input_file.pcm output_file.pcm
Try `ATE --help' or `ATE --usage' for more information.
threads: 2, bass: 4, treble: 4
opening file input.pcm
RUNNING!
done, saving to out.pcm
When running my program, I get "too few arguments", even though argp succesfully parsed the input and output option, as you can see in the output.
Printing out the number of arguments in parse_opt, cout << state->arg_num << endl; gives me 0's at every call.
The code is a little long, but it's completely self-contained so you can compile it to see for yourself.
commands.cpp
using namespace std;
#include <stdlib.h>
#include <argp.h>
#include <iostream>
#include <string>
#include <errno.h>
struct arguments {
string input_file;
string output_file;
int threads;
int bass;
int treble;
};
static char doc[] = "Parallequaliser - a multithreaded equaliser application written in c++";
static char args_doc[] = "-p AMOUNT_OF_THREADS -b BASS_INTENSITY -t TREBLE_INTENSITY input_file.pcm output_file.pcm";
static struct argp_option options[] = {
{"input_file", 'i', "IN_FILE", 0, "an input file in pcm format"},
{"output_file", 'o', "OUT_FILE", 0, "an output file in pcm format"},
{"threads", 'p', "AMOUNT_OF_THREADS", OPTION_ARG_OPTIONAL, "amount of threads, min 2"},
{"bass", 'b', "BASS_INTENSITY", OPTION_ARG_OPTIONAL, "bass intensity, from 0 to 7"},
{"treble", 't', "TREBLE_INTENSITY", OPTION_ARG_OPTIONAL, "treble intensity, from 0 to 7"},
{0}
};
static error_t parse_opt (int key, char *arg, struct argp_state *state) {
struct arguments *arguments = (struct arguments *) state->input;
switch (key) {
case 'p':
if (arg == NULL) {
arguments->threads = 4;
} else {
arguments->threads = strtol(arg, NULL, 10);
}
break;
case 'b':
if (arg == NULL) {
arguments->bass = 4;
} else {
arguments->bass = strtol(arg, NULL, 10);
}
break;
case 't':
if (arg == NULL) {
arguments->treble = 4;
} else {
arguments->treble = strtol(arg, NULL, 10);
}
break;
case 'i':
if (arg == NULL) {
cout << "You forgot to specify the input file using the -i input_file.pcm option" << endl;
} else {
arguments->input_file = (string) arg;
}
break;
case 'o':
if (arg == NULL) {
cout << "You forgot to specify the out file using the -i output_file.pcm option" << endl;
} else {
arguments->output_file = (string) arg;
}
break;
case ARGP_KEY_ARG:
cout << "Key arg... " << key << endl;
if (state->arg_num > 5){
cout << "Too many arguments!" << endl;
argp_usage(state);
}
break;
case ARGP_KEY_END:
if (state->arg_num < 2){
cout << "Too few arguments!" << endl;
argp_usage(state);
}
break;
default:
return ARGP_ERR_UNKNOWN;
}
return 0;
}
static struct argp argp = { options, parse_opt, args_doc, doc };
int main (int argc, char **argv) {
struct arguments arguments;
arguments.threads = 2;
arguments.bass = 4;
arguments.treble = 4;
argp_parse(&argp, argc, argv, ARGP_NO_EXIT, 0, &arguments);
cout << "threads: " << arguments.threads << ", bass: " << arguments.bass << ", treble: " << arguments.treble << endl;
cout << "opening file " << arguments.input_file << endl;
cout << "RUNNING!" << endl;
cout << "done, saving to " << arguments.output_file << endl;
return 0;
}

Answer 1

The options don't count as "arguments" for the context of the argp parser.
When running ./ATE -i input_file.pcm -o output_file.pcm, you have "too few arguments" because you reach ARGP_KEY_END, the end of the arguments, with no arguments left. arg_num represents the "stand-alone" arguments : the number of ARGP_KEY_ARG arguments that have been processed. You don't have any.
To make sure you have the two required arguments as you initialy wanted, check that you don't reach ARGP_KEY_END without having seen two arguments (like you are already doing : the too few arguments would mean you don't have your two filenames). The case ARGP_KEY_ARG is where you get the values of the arguments.