parse_known_args

[p-ranav]

Closes #181

This PR adds a parse_known_args support.

Sometimes a program may only parse a few of the command-line arguments, passing the remaining arguments on to another script or program. In these cases, the parse_known_args() function can be useful. It works much like parse_args() except that it does not produce an error when extra arguments are present. Instead, it returns a list of remaining argument strings.

#include <argparse/argparse.hpp>
#include <cassert>

int main(int argc, char *argv[]) {
  argparse::ArgumentParser program("test");
  program.add_argument("--foo").implicit_value(true).default_value(false);
  program.add_argument("bar");

  auto unknown_args =
    program.parse_known_args({"test", "--foo", "--badger", "BAR", "spam"});

  assert(program.get<bool>("--foo") == true);
  assert(program.get<std::string>("bar") == std::string{"BAR"});
  assert((unknown_args == std::vector<std::string>{"--badger", "spam"}));
}

[tt2468]

Thanks for this!