What does it mean when a member function is volatile? [duplicate]

Question

I normally see the const specifier used to indicate a const member function. But what does it mean when the volatile keyword is used?

void f() volatile {}

This compiles fine for me but I don't understand what this is for. I couldn't find any information about this in my search so any help is appreciated.

Update: To make it clear, I know what volatile is for. I just don't know what it means in this context.

Answer 1

On a member function, const and volatile qualifiers apply to *this. Accesses of any instance members within that member function would then be volatile accesses, with the same semantics as any volatile variable. In particular, non-volatile member functions cannot be called on a volatile object, and volatile applies to overloading in the same way as const:

#include <iostream>

class C {
public:

    void f() {
        std::cout << "f()\n";
    }

    void f() const {
        std::cout << "f() const\n";
    }

    void f() volatile {
        std::cout << "f() volatile\n";
    }

    void f() const volatile {
        std::cout << "f() const volatile\n";
    }

};

int main() {

    C c1;
    c1.f();

    const C c2;
    c2.f();

    volatile C c3;
    c3.f();

    const volatile C c4;
    c4.f();

}