Question about private nested classes/structs

Hello,

can someone please tell me, why it's possible to access the member of a returned private nested struct? Shouldn't the compiler complain about the privateness of the returned data type?

Code:

---

#include <iostream>

using std::cout;
using std::endl;

class TestClass
{
private:
    struct TestStruct
    {
        int A, B, C;
    };

public:
    TestStruct get()
    {
        TestStruct t = { 1, 2, 3 };
        return t;
    }
};

int main( int argc, char **argv )
{
    TestClass *t = new TestClass();

    // Here the compiler mourns about privateness - as expected
    TestClass::TestStruct e = t->get();

    // This one works, but why?
    int a = t->get().A;
}

---

Thanks,
egrath

The type itself is private but the members are public.

By having a public method return a TestStruct you effectively negate the privateness of it. If you want TestStruct to be private then you shouldn't return any TestStruct through public methods.

The problem really becomes apparent with C++0x's type inference. You can infer the returned TestStruct type and then start instantiating as many TestStructs as you like outside of TestClass.

Hello,
thanks you for bringing light to this issue!
egrath

Why are you creating a new instance via new?

Hello Elysia,

what's wrong with creating a new instance via new?

egrath

What is the point? Do you need it? Are you aware of the overhead? Are you aware that you're creating a memory leak? Why aren't you wrapping the raw pointer in a smart pointer?

Hello Elysia,

the code i've posted when starting the thread is just an example because i wanted to add some code to the question for better understanding - think of it as working pseudo code which has nothing to do with real life code and good coding practices.

egrath

Of course. I just want to make sure you don't do anything silly in your real code.
As long as you understand the goods and bads of it, then it's fine.