FancyArgumentParser

A single-header, dependency-free C++ command-line argument parser.

Argparse-style ergonomics for C++ — named & positional arguments, type casting, choices, defaults, auto-generated help, and Python-like keyword arguments in C++20.

Tutorial · Examples · Class reference

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Why

Drop one header into your project and get a fully featured argument parser — no submodules, no CMake packages, no linking. Everything lives in argparse.h.

Features

• 🧩 Single header, zero dependencies — just #include "argparse.h".
• 🏷️ Named and positional arguments, freely mixed.
• 🔢 Typed values — int, long long, double, bool, and string.
• 🎚️ Flexible arity — fixed counts, kAnyArgCount (zero-or-more), kFromOneToInfiniteArgCount (one-or-more), or flags (zero values).
• ✅ Validation — required/optional, value choices, and defaults.
• 📖 Auto-generated help & usage, with custom epilogue and overridable usage line.
• 🔤 Long-option abbreviations (--verb → --verbose when unambiguous).
• ⚙️ Configurable — custom prefix characters, ignore-unknown args, custom namespace.
• 🆕 Three declaration styles, including Python-like keyword arguments in C++20.
• 🧪 Tested across Linux, macOS and Windows on C++17/20/23.

Quick start

Copy argparse.h into your project — that's the whole installation.

#include <iostream>
#include "argparse.h"

int main(int argc, char** argv)
{
    auto parser = argparse::ArgumentParser("greet").SetDescription("A tiny greeter");

    parser.AddArgument(argparse::CreateNamedArgument("n", "name", 1,
        argparse::ArgTypeCast::e_String, true).SetHelp("Who to greet"));
    parser.AddArgument(argparse::CreateNamedArgument("c", "count", 1,
        argparse::ArgTypeCast::e_int, false).SetDefault(1).SetHelp("How many times"));

    auto obj = parser.ParseArgs(argc, argv);
    if (!obj.IsArgValid())
    {
        std::cout << obj.GetErrorString() << "\n" << parser.GetHelp(80) << std::endl;
        return 1;
    }

    auto name = obj.GetArg("name");
    for (int i = 0; i < obj.GetArg("count").GetAsInt(); ++i)
        std::cout << "Hello, " << name.GetAsString() << "!\n";
    return 0;
}

$ c++ -std=c++17 greet.cpp -o greet
$ ./greet --name World --count 2
Hello, World!
Hello, World!

Three ways to declare an argument

Pick whichever reads best — they build the same argument.

// 1. Fluent setters
parser.AddArgument(argparse::CreateNamedArgument()
    .SetShortName("n").SetLongName("numbers")
    .SetType(argparse::ArgTypeCast::e_int)
    .SetAnyNumberOfArgumentsButAtLeastOne());

// 2. Positional factory arguments
parser.AddArgument(argparse::CreateNamedArgument("n", "numbers",
    argparse::kFromOneToInfiniteArgCount, argparse::ArgTypeCast::e_int));

// 3. Keyword style — Python-like, needs C++20 designated initializers
parser.AddArgument(argparse::CreateNamedArgument({
    .shortName = "n",
    .longName  = "numbers",
    .nargs     = argparse::kFromOneToInfiniteArgCount,
    .type      = argparse::ArgTypeCast::e_int}));

Note: every argument is required by default — call SetRequired(false) (or set required = false) to make one optional.

Requirements

• A C++11 compiler or newer. The library is continuously tested on C++17, C++20 and C++23 across Linux, macOS and Windows.
• The std::any-based Get() accessor is available from C++17 onward; the typed getters (GetAsInt(), GetAsVecInt(), …) work in every standard.
• Designated-initializer (keyword) argument construction needs C++20.

Building the tests

The tests live under tests/ and are never included by the header, so consumers can ignore them entirely.

cmake -S tests -B build
cmake --build build
ctest --test-dir build --output-on-failure

Override the standard with -DCMAKE_CXX_STANDARD=20 (or 23).

Documentation

• 📘 Tutorial — step-by-step introduction.
• 📗 Examples — flags, choices, positional/named mixes, bool, ranges, keyword args, and more.
• 📙 Class reference — full API overview.
• 📓 About — project background.

License

Released under the MIT License — see the header of argparse.h for the full text. © 2021 simfeo.