How to determine if a class has no class deriving from it?

Question

How to determine if a class has no class deriving from it? Any type-traits methods help?

I want to write out some data. The data is created via a pointer like

unique_ptr<A> a(new A);

If class A has no sub-class, I just write out the data content. If A has subclasses, I will write out its concrete type first, and then write the data content. When reading the data, after reading the concrete type, I know using what concrete type to create the pointer and then read the data content. Thus, I think I have to determine if A has subclass or not?

What problem are you trying to solve? There is probably a better way. This sounds like an [X-Y problem](https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem). — Greg Hewgill, Feb 26 '14 at 19:12
I don't think this is possible, due to separate compilation. I agree that you should post what you're trying to accomplish. — , Feb 26 '14 at 19:13
Give `A` a virtual method that writes out what you need. And read [a good C++ book](http://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). — juanchopanza, Feb 26 '14 at 19:22
@juanchopanza If it is simple, would you give me an example? I appreciate it. — user1899020, Feb 26 '14 at 19:25

score 1 · Answer 1 · answered Feb 26 '14 at 19:14

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Thats not possible, because a class doesn't know what (If exists) class derives from it.

What you could check is if a class derives from another:

struct foo {};

struct bar : foo {};

static_assert( std::is_base_of<foo,bar>::value );

answered Feb 26 '14 at 19:14

Manu343726

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score 1 · Accepted Answer · answered Feb 26 '14 at 19:22

1

In C++11, you can declare a class final. This makes sure that no class can derive from it. See http://en.cppreference.com/w/cpp/language/final.

answered Feb 26 '14 at 19:22

Christian Hackl

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How to determine if a class has no class deriving from it?

2 Answers2