What is the purpose of a volatile member function in C++?

Question

What is the purpose of a volatile member function in C++?

Answer 1

To answer the question about what it means to have a 'volatile member function' (which may or may not be what was originally intended by the person who posted the question), marking a member function as const or volatile (or a combined const volatile) applies those qualifiers to the this pointer used in the function. As stated by the standard (9.2.1 "The this pointer"):

The type of this in a member function of a class X is X*. If the member function is declared const, the type of this is const X*, if the member function is declared volatile, the type of this is volatile X*, and if the member function is declared const volatile, the type of this is const volatile X*.

So by marking the member function as volatile you'd be making any access to the non-static data members of the object within that member function as volatile.

Answer 2

EDIT:

This answer was posted when the question was about the volatile keyword. Question seems to have been changed by a third party.

ORIGINAL:

Volatile informs the compiler that it should not assume that the value it just put in the variable marked as volatile will be there next time it uses it... that it must check the current value before using it again.

One example is if the variable represents a memory location that might be changed by another process.

Here's an example (been ages since I did C++ so please forgive any minor syntax issues):

volatile int x;  int DoSomething() {     x = 1;      DoSomeOtherStuff();      return x+1; // Don't just return 2 because we stored a 1 in x.                   // Check to get its current value }