Arg Parsing

Simulant provides a simple way to pass command line options to your application. To use this functionality you'll need to do the following:

1. Define arguments in your smlt::Application subclass constructor
2. Pass argc, and argv to Application::run()
3. Access the values

Defining arguments

Defining arguments is simple, here's an example from the Particles sample:

    args->define_arg("--stress", smlt::ARG_TYPE_BOOLEAN, "stress test the particle system");
    args->define_arg("--filename", smlt::ARG_TYPE_STRING, "display the selected file");

args is a property on the Application. The first param must start with a double-hyphen and is the argument that can be passed on the command line. The type can be: boolean, string, float or integer.

Finally the last argument is the help text displayed when someone runs your application with the --help flag.

Accessing values

You can access the values using the arg_value template function:

    auto maybe_value = app->args->arg_value<bool>("stress");  // Access the value
    auto maybe_value = app->args->arg_value<bool>("stress", false); // Specify a default

The returned value is not the final value. arg_value<T> returns an optional<T>:

    if(maybe_value.has_value()) {
        auto final_value = maybe_value.value();
    }

If you passed a default to arg_value<T>() then has_value() will always return true. Otherwise has_value() will return false if the user didn't pass a value for this param.

Notice that the name passed to arg_value<T>() doesn't need the leading hyphens. The name of this variable can be defined by passing a custom var_name to define_arg.