CLI20 — Define your CLI as a type, not as a builder.

Define your CLI as a type, not as a builder.

#include "cli/argument.hh"
#include "cli/parser.hh"

struct Args {
  cli::Flag<"verbose", 'v'>          verbose;
  cli::StringOption<"output", 'o'>   output;
  cli::Positional<std::string,
    cli::nargs::one_or_more>         inputs;
};

auto main(int argc, char* argv[]) -> int {
  const auto args = cli::parse_or_exit<Args>(argc, argv);
}

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📦

Header-only

Drop include/ into your project. No linking, no runtime overhead.

⚡

C++20 native

Compile-time option names, concepts, constexpr. Built for modern C++.

🔒

Type-safe schema

Your CLI is a struct. No string lookups at runtime.

✨

Zero macros

Clean modern C++. No registration macros anywhere.

🌿

Subcommands

Nested structs compose naturally. Recursive by design.

📖

Auto help

Add cli::Help<> help; and get full formatted help output.

CLI11 → CLI20

Before (CLI11)

CLI::App app{"my app"};
bool verbose = false;
std::string output;

app.add_flag("-v,--verbose", verbose);
app.add_option("-o,--output", output);
CLI11_PARSE(app, argc, argv);

After (CLI20)

struct Args {
  cli::Flag<"verbose", 'v'>        verbose;
  cli::StringOption<"output", 'o'> output;
};

const auto args =
  cli::parse_or_exit<Args>(argc, argv);