Volatile Member Functions (C++)

Question

Given the following class:

class MyClass {
  public:
    int value() const {
      return value_;
    }

  private:
    volatile int value_;
};

Does the value() member function also have to be marked as volatile to avoid getting optimized away or is it okay as written? Thanks.

Answer 1

It is completely analogous to how const works.

If you have a const object, only member functions marked const are callable.

And so...

If you have a volatile object, only member functions marked volatile are callable.

As long as the object itself is not volatile, it makes no difference whether the function is.

However, do keep in mind that volatile has nothing to do with multithreading, and it will not help you write thread-safe code. It is the wrong tool for anything concurrency-related.

Answer 2

Does the value() member function also have to be marked as volatile to avoid getting optimized away or is it okay as written?

Marking the member function volatile will have no effect on whether it is optimized away or not. It is fine as written.

The worry is if I have MyClass c; and then call c.value(); a couple times, the compiler might think c.value() will return the same value (even though it could have possibly changed..)

It sounds like what you want is to learn about atomic variables. Take a look at std::atomic.

If you really want to learn about volatile, read this paper: http://www.cs.utah.edu/~regehr/papers/emsoft08-preprint.pdf