What is the nullptr keyword, and why is it better than NULL?
c++, c++11, nullptr, pointers
Solution
How is it a keyword and an instance of a type?
This isn't surprising. Both `true` and `false` are keywords and as literals they have a type ( `bool` ). `nullptr` is a pointer literal of type `std::nullptr_t`, and it's a prvalue (you cannot take the address of it using `&`).
`4.10` about pointer conversion says that a prvalue of type `std::nullptr_t` is a null pointer constant, and that an integral null pointer constant can be converted to `std::nullptr_t`. The opposite direction is not allowed. This allows overloading a function for both pointers and integers, and passing `nullptr` to select the pointer version. Passing `NULL` or `0` would confusingly select the `int` version.
A cast of `nullptr_t` to an integral type needs a `reinterpret_cast`, and has the same semantics as a cast of `(void*)0` to an integral type (mapping implementation defined). A `reinterpret_cast` cannot convert `nullptr_t` to any pointer type. Rely on the implicit conversion if possible or use `static_cast`.
The Standard requires that `sizeof(nullptr_t)` be `sizeof(void*)`.
Problem
We now have C++11 with many new features. An interesting and confusing one (at least for me) is the new `nullptr`. Well, no need anymore for the nasty macro `NULL`. ``` int* x = nullptr; myclass* obj = nullptr; ``` Still, I am not getting how `nullptr` works. For example, Wikipedia article says: C++11 corrects this by introducing a new keyword to serve as a distinguished null pointer constant: nullptr. It is of type nullptr_t, which is implicitly convertible and comparable to any pointer type or pointer-to-member type. It is not implicitly convertible or comparable to integral types, except for bool. How is it a keyword and an instance of a type? Also, do you have another example (beside the Wikipedia one) where `nullptr` is superior to good old `0`?