Can't define ++ operator in C++, what's the issue here?

Question

I\'m working through Bjarne Stroustrup\'s The C++ Programming Language and I\'m stuck on one of the examples. Here\'s the code, and aside from whitespace differences and comment

Answer 1

You have a couple of problems:

First, you are attempting to implement a function (operator++) inside another function (main). C++ does not allow this (with the exception of lambdas).

Second, you are only implementing a prefix increment, so ++light will work, but light++ will not. You should implement them both. An example of it can be found here.

Answer 2

Traffic_light& operator++(Traffic_light& t) is a function with name operator ++. Each function shall be defined outside any other function. So place the definition of the operator before main.

Answer 3

Here you have your code running:

http://coliru.stacked-crooked.com/a/74c0cbc5a8c48e47

#include <iostream>
#include <string>
#include <vector>

enum class Traffic_light { 
    green, 
    yellow, 
    red
};

Traffic_light & operator++(Traffic_light & t) {
    switch (t) {
        case Traffic_light::green:
            t = Traffic_light::yellow;
        break;
        case Traffic_light::yellow:
            t = Traffic_light::red;
        break;
        case Traffic_light::red:
            t = Traffic_light::green;
        break;
    }
    return t;
}

std::ostream& operator<<(std::ostream& os, Traffic_light & t)
{
    switch(t)
    {
        case Traffic_light::green:
            os << "green";
        break;
        case Traffic_light::yellow:
            os << "yellow";
        break;
        case Traffic_light::red:
            os << "red";
        break;
    }
    return os;

}

int main()
{
    Traffic_light light = Traffic_light::red;

    std::cout << "Ligth:" << ++light << std::endl;
    std::cout << "Ligth:" << ++light << std::endl;
    std::cout << "Ligth:" << ++light << std::endl;

    return 0;
}