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c++c++11nullptr
Moiz Sajid
Moiz Sajid

Reputation: 675

What is the difference between nullptr and nullptr_t in C++?

Which one should I use? Any advantages if I use one over the other?

Upvotes: 23

Views: 12619

Answers (7)

πάντα ῥεῖ
πάντα ῥεῖ

Reputation: 1

"... if I use one over the other?"

You can't (use one over the other) they're orthogonal by these means:

nullptr_t is the type used to represent a nullptr

nullptr is (1)effectively a constant of type nullptr_t that represents a specific compiler implementation defined value.

See the C++11 standards section:

2.14.7 Pointer literals

  1. The pointer literal is the keyword nullptr. It is a prvalue of type std::nullptr_t.
    [ Note: std::nullptr_t is a distinct type that is neither a pointer type nor a pointer to member type; rather, a prvalue of this type is a null pointer constant and can be converted to a null pointer value or null member pointer value. See 4.10 and 4.11. — end note ]

1) Just like the this keyword nullptr stands for an rvalue rather than being of const type. Thus, decltype(nullptr) can be a non-const type. With Visual C++ 2015 and MinGW g++ 5.1 it is non-const.

Upvotes: 9

Barry
Barry

Reputation: 302932

From [lex.nullptr]:

Pointer Literals

pointer-literal:
     nullptr

The pointer literal is the keyword nullptr. It is a prvalue of type std::nullptr_t. [ Note: std::nullptr_t is a distinct type that is neither a pointer type nor a pointer to member type; rather, a prvalue of this type is a null pointer constant and can be converted to a null pointer value or null member pointer value. See 4.10 and 4.11. —end note ]

So use nullptr when you need a pointer literal, and std::nullptr_t in a context when you need to take that type. The latter, for instance, if you're making a function or constructor or something that can take a nullptr as an argument.

Upvotes: 3

julian.757
julian.757

Reputation: 163

In exactly the same way that true is a C++ keyword literal of type bool, nullptr is a C++ keyword literal of type std::nullptr_t.

Upvotes: 7

Vlad from Moscow
Vlad from Moscow

Reputation: 310980

nullptr is a pointer literal of type std::nullptr_t. And moreover nullptr is also a keyword of the C++ the same way as boolean literals false and true.:)

Upvotes: 3

Karlis Olte
Karlis Olte

Reputation: 353

If you try this

cout << typeid(nullptr).name() << endl;

you will see that nullptr is of type std::nullptr_t.

Upvotes: 3

Quentin
Quentin

Reputation: 63124

nullptr is the constant, nullptr_t is its type. Use each one in contexts where you need respectively a null pointer, or the type of a null pointer.

Upvotes: 37

Sam Estep
Sam Estep

Reputation: 13304

nullptr is of type nullptr_t.

Upvotes: 5

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