Parsing conmmand line arguments is a tedious task and many programming languages have libraries for it. While researching such libraries for C++
I found Lyra which works as a header-only library for C++11 and higher.
It supports the usual positional and optional arguments known from POSIX style command line tools and has the possibility to automatically generate a help text.
For a full set of examples see the documentation.
Example: Optional Arguments and Help Text
#include <iostream>
#include <lyra/lyra.hpp>
int main(int argc, const char** argv)
{
// Variables to put arguments into:
int width = 0;
int height = 0;
bool show_help = false;
const auto cli = lyra::help(show_help)
| lyra::opt(width, "width")
["-w"]["--width"]("How wide should it be?")
| lyra::opt(height, "height")
["-x"]["--height"]("How high should it be?");
// Parse the program arguments:
const auto result = cli.parse({ argc, argv });
if (!result)
{
std::cerr << result.errorMessage() << std::endl;
std::cerr << cli;
exit(1);
}
if(show_help)
{
std::cout << cli << '\n';
exit(0);
}
std::cout << "width * height: " << width * height << '\n';
}
Starting the programm without arguments yields the default values, using -h triggers the help text:
./a.out
width * height: 0
./a.out -w 15 -x 10
width * height: 150
./a.out -h
Usage:
a.out [-?|-h|--help] [-w|--width] [-x|--height]
Options, arguments:
-?, -h, --help
Display usage information.
-w, --width <width>
How wide should it be?
-x, --height <height>
How high should it be?
Entering wrong arguments also leads to the help text being printed
./a.out --blabla dddd
Unrecognized token: --blabla
Usage:
a.out [-?|-h|--help] [-w|--width] [-x|--height]
Options, arguments:
-?, -h, --help
Display usage information.
-w, --width <width>
How wide should it be?
-x, --height <height>
How high should it be?
Non-optional Arguments
Non-optional parameters can be specified by using lyra::arg instead of lyra::opt. Non-optional arguments are just specified by their position in the CLI.
const auto cli = lyra::help(show_help)
| lyra::arg(width, "width")("How wide?")
| lyra::arg(height, "height")("How high should it be?");
./a.out
width * height: 0
./a.out 10 10
width * height: 100
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