如何在嵌套类中初始化成员？ C ++

Question

I have a problem with initializing members of class inside class. Let's say that I want to set diameter, width and volume to 1 just like I set x to 1

struct car {
    int x;
    struct wheels {
        int diameter;
        int width;
    };
    struct engine {
        int volume;
    };
    car();
    car(wheels w, engine e);
};

car::car() : x(1), wheels::diameter(1), wheels::width(1) {}

I also tried do it like this but with no luck:

car::car() : x(1), wheels{ 1,1 } {}

Answer 1

Your class declares the nested classes wheels and engine , but it doesn't actually contain member variables of type wheels or type engine . It's pretty easy to fix this:

struct car {
    struct Wheels {
        int diameter;
        int width;
    };
    struct Engine {
        int volume;
    };

    int x;
    Wheels wheels;
    Engine engine;
    car() : x(1), wheels{1,1}, engine{} {}
    car(Wheels w, Engine e) : x(1), wheels(w), engine(e) {}
};

Answer 2

wheels and engine are just types, there are no data members of those types in your car struct, the only data member is x .

I think you probably meant to do something like this instead:

struct car {
    struct wheels {
        int diameter;
        int width;
    };
    struct engine {
        int volume;
    };
    int x;
    wheels w;
    engine e;
    car();
    car(wheels w, engine e);
};

car::car() : x(1), w{1, 1}, e{1} {}

car::car(wheels w, engine e) : x(1), w(w), e(e) {}

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