Defined in header <cstddef> | ||
---|---|---|
typedef decltype(nullptr) nullptr_t; | (since C++11) |
std::nullptr_t
is the type of the null pointer literal, nullptr
. It is a distinct type that is not itself a pointer type or a pointer to member type.
If two or more overloads accept different pointer types, an overload for std::nullptr_t
is necessary to accept a null pointer argument.
#include <cstddef> #include <iostream> void f(int* pi) { std::cout << "Pointer to integer overload\n"; } void f(double* pd) { std::cout << "Pointer to double overload\n"; } void f(std::nullptr_t nullp) { std::cout << "null pointer overload\n"; } int main() { int* pi; double* pd; f(pi); f(pd); f(nullptr); // would be ambiguous without void f(nullptr_t) // f(0); // ambiguous call: all three functions are candidates // f(NULL); // ambiguous if NULL is an integral null pointer constant // (as is the case in most implementations) }
Output:
Pointer to integer overload Pointer to double overload null pointer overload
nullptr | the pointer literal which specifies a null pointer value (C++11) |
implementation-defined null pointer constant (macro constant) |
|
(C++14) | checks if a type is std::nullptr_t (class template) |
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