Question

I have been reading through other questions on here and there is something that has me confused and hopefully it can be explained. I am sure there it is a simple thing but it is alluding me.

So in C++ we have private variables that are only viewable within the class:

class MyClass
{
    private:
        int i;
};

But we can also have unnamed namespaces:

namespace
{
    int i;
}

Both appear to be private to the class but in the 2nd case you cannot see they exist from the header file. From reading other questions it seems that functions are different as you can’t pass class objects to them? But I am not sure what the difference is here for variables.

Is there a disadvantage to the 2nd way that means you should still use private variables?

Answer 1

They aren’t the same.

Integer i in the anonymous namespace will be shared by all instances of MyClass.

The private integer i in MyClass will be unique for each instantiation of the class.

The equivalent using private would be to make i static:

//.h
class MyClass
{
    private:
        static int i;
};

And instantiate the one single shared i like this:

//.cpp
int MyClass::i = 0;