Accessing string on private std::string inheritance

Question

I have seen this example from the book:

class Test: private std::string
{
public:
    Test():std::string("How?")
    {
    }
};

int main(int argc, char** argv)
{
    Test t;

    std::cout<<(std::string&)t<<std::endl;

    return 0;
}

I don't know how did it printed "how" when i typecasted the class name? is it because of operators? but i know that when you do private inheritance, the public and protected variables and methods will be considered "private" outside.

So my question is, how did it exactly printed "How" ?

edit :

so who is holding the string value "How" and how was it printed? Because it was printed by typecasting.

Answer 1

This illustrates one of the dangers of the C-style cast : it's the only cast that ignores inheritance access specifiers. As you saw, the cast successfully dug out the std::string base reference, even though it was private. If you try this with a static_cast, it won't compile.

Edit :

The std::string subobject of t is holding "How", as you initialized it in Test's constructor. Casting to a reference to a base class serves to access the corresponding subobject.

Answer 2

The cast (std::string&)t casts t to a reference to an instance of its base class std::string. C style casts are the only casts that can cast to an inaccessible base class. The effect is the same as with an ordinary implicit conversion to an accessible base class.