std::nullptr_t
From cppreference.com
| Defined in header
<cstddef>
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||
| typedef decltype(nullptr) nullptr_t;
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(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.
[edit] Example
If two or more overloads accept different pointer types, an overload for std::nullptr_t is necessary to accept a null pointer argument.
Run this code
#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(NULL); // ambiguous overload: all three functions are candidates }
Output:
Pointer to integer overload Pointer to double overload null pointer overload
[edit] See also
| nullptr | the pointer literal which specifies a null pointer value (C++11) |
| implementation-defined null pointer constant (macro constant) |
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| (C++14)
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checks if a type is std::nullptr_t (class template) |