Arg3P

Single-Header C++20 argument parsing library.

Introduction

Arg3P is a small & header-only argument parser designed for C++20. It provides a simple, type-safe interface for defining command-line options with short and/or long names. Boolean arguments act as flags, while all other argument types consume a following value.

Features

• Header-only & dependency free
• Supports both short (-a) and long (--alpha) options.
• Short options may be grouped: -abc == -a -b -c.
  • Only one non-boolean (value-taking) option may appear in a group & must be the last to appear.
• Positional arguments may be specified to appear before and after flagged arguments through the PositionalArgument class.
• Automatic type converesion for fundamental and string-constructible types.
• Clean, type-safe design using modern C++20 concepts and ranges.

Examples

See the examples/ directory for more comprehensive examples.

// see examples/basic.cpp

#include <iostream>

#include <Arg3P/Arg3P.hpp>

int
main(int argc, const char *argv[])
{
	using namespace Arg3P;

	// Define command-line arguments
	auto verbose =
		Arg<bool>::makeRequired('v', "verbose", "enable verbose output");
	auto input =
		Arg<std::string>::makeRequired('i', "input", "set the input file path");
	auto threads =
		Arg<int>::makeRequired("threads", "set the number of worker threads");

	// Register arguments with the parser
	Parser<const char *> parser{{input, threads, verbose}};

	// Parse command line (skip program name)
	const std::optional<Error> error = parser(std::span(argv + 1, argc - 1));
	if(error.has_value()) {
		std::cerr << "Error parsing argument: "
				  << errorName(error.value().error) << ": "
				  << error.value().message << "\n";
		return 1;
	}

	// Access results
	std::cout << "Verbose: " << verbose->get().value_or(false) << "\n";
	std::cout << "Input:   " << input->get().value_or("<none>") << "\n";
	std::cout << "Threads: " << threads->get().value_or(1) << "\n";
}

Implementation Notes

• Boolean arguments (Arg<bool>) act as flags and take no value.
• Non-boolean arguments consume the next command-line token as a value.
• Grouped short options (-abc) expand left to right; the last may take a value.
• When there are front and back positional arguments expected and there are more non-flagged arguments provided before any flagged arguments appear, these are interpreted as the back positional arguments.

License

Arg3P is licensed under the BSD 2-Clause license, see the LICENSE file or https://opensource.org/license/BSD-2-Clause for a copy of the License.