Question

What is the lifetime of a C++ class member. For example, at which time will the std::fstream of a Foo object be released? When entering the destructor or when leaving the destructor? Is this defined in the C++ standard?

struct Foo
{
    std::fstream mystream;
    ~Foo()
    {
        // wait for thread writing to mystream
    }
};

Answer 1

The mystream data member is destroyed during the destruction of the Foo object, after the body of ~Foo() is executed. C++11 §12.4[class.dtor]/8 states:

After executing the body of the destructor and destroying any automatic objects allocated within the body, a destructor for class X calls the destructors for X‘s direct non-variant non-static data members, the destructors for X‘s direct base classes and, if X is the type of the most derived class, its destructor calls the destructors for X‘s virtual base classes.

mystream is a non-variant, non-static data member of Foo (a variant data member is a member of a union; Foo is not a union).