C++ public enum in namespace of class

Question

I am making a class and I want to create an enum inside that class so that it can only be accessed through the namespace of that class. I would want users to be able to access the enum outside of the class like so:

GpioPin pin(23, GpioPin::OUTPUT);

where GpioPin is the class and OUTPUT is one of the enum values.

I tried putting the enum at the top of the class and I tried putting it under the public label like (constructor included for help debugging):

public:
    enum pin_dir {
        INPUT,
        OUTPUT,
    };

    GpioPin(int pin_num, pin_dir dir): pin_num(pin_num), dir(dir) {
        std::string dir_str; 
        if(dir == INPUT){
            dir_str = "in";
        } else if (dir == OUTPUT){
            dir_str = "out";
        } else {
            std::cout << "invalid direction in constructor for pin " << pin_num << std::endl;
            return;
        }

        init_gpio_pin(pin_num, dir_str.c_str());
    }

but when under the public tag the constructor acts like the enum doesn't exist and throws a compiler error.

Does anyone know the proper way to do this?

Thanks

Edit: the problem has been solved. The code that is depicted here is correct and works as intended. The accepted answer gives some good information about enum class in C++

Answer 1

Look at enum class (google for c++ enum class).

Class Foo {
public:
    enum class Color{ Red, Green, Blue};
};

Then, you reference things as:

Foo::Color::Red

Works great.