Skip to main content

Simple API

This is the first example to open when you want the default cli20 flow. It shows the smallest useful cli20 program: one flag, one optional named argument, and one required positional input.

Source​

Source: examples/simple_api.cc

examples/simple_api.cc
#include <iostream>

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

struct Args {
  cli::Description description{
      "Minimal cli20 program with one flag, one option, and one positional."};
  cli::Help<> help;
  cli::Flag<"verbose", 'v'> verbose{{.help = "Enable verbose logging"}};
  cli::StringOption<"output", 'o'> output{{.help = "Optional output file"}};
  cli::Positional<std::string> input{
      {.help = "Input file", .presence = cli::required}};
};

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

  if (args.verbose.value()) {
    std::cout << "verbose: true\n";
  }
  if (args.output) {
    std::cout << "output: " << *args.output << '\n';
  }
  std::cout << "input: " << *args.input << '\n';
  return 0;
}

What This Example Shows​

This example declares a CLI as ordinary typed fields, mixes a flag with an optional named value and a required positional, and lets cli20 handle standard help and error flow. On success, verbose becomes a bool, output holds an optional path-like string, and input holds the required file name.

Try It​

cli20@cli20-dev: ~
cli20@cli20-dev:~$ simple_api

Things to try:

  • Happy path — --verbose --output result.txt input.cc
  • No flag — input.cc (just the required positional)
  • Help — --help
  • Missing positional — --verbose to see the required-argument error