Sample using getopt.

params_CMakeLists.txt

cmake_minimum_required(VERSION 3.9)
project(params)

set(CMAKE_CXX_STANDARD 98)

add_executable(params main.cpp)

params_main.cpp

#include <iostream>
#include <cstdlib>
#include <unistd.h>
#include <sstream>

using namespace std;

int main(int argc, char **argv) {
    cout << "Parametros" << endl;

    int procs, opt;
    stringstream loglevel;

    if (argc < 2) {
        cerr << "Show usage here! "<< endl;
        return EXIT_FAILURE;
    }

    // Parameters
    while ((opt = getopt(argc, argv, ":n:l:")) != -1) {
        switch (opt) {
            case 'n':
                procs = atoi(optarg);
                break;
            case 'l':
                loglevel.str(string());
                loglevel << optarg;
                break;
            case ':':
                // Exemplo: -n 10 -l
                cerr << "Faltando valor para o parametro: " << (char) optopt << endl;
                return EXIT_FAILURE;
            case '?':
                // Exemplo: -n 10 -l info -w
                cerr << "Parametro desconhecido: " << (char) optopt << endl;
                return EXIT_FAILURE;
            default:
                cerr << "Erro de parametros" << endl;
                return EXIT_FAILURE;
        }
    }

    if (loglevel.str().size() == 0) {
        // Exemplo: -n 10
        cerr << "LogLevel invalido" << endl;
        return EXIT_FAILURE;
    }

    if (optind < argc) {
        cerr << "Argumento invalido: " << argv[optind] << endl;
        return EXIT_FAILURE;
    }

    if (optind > argc) {
        cerr << "Erro de parametros" << endl;
        return EXIT_FAILURE;
    }

    cout << "Processos: " << procs << endl;
    cout << "LogLevel:  " << loglevel.str() << endl;

    return EXIT_SUCCESS;
}