nullptr, the pointer literal

C++

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User-defined conversion

Syntax

nullptr		(since C++11)

Explanation

The keyword nullptr denotes the pointer literal. It is a prvalue of type std::nullptr_t. There exist implicit conversions from nullptr to null pointer value of any pointer type and any pointer to member type. Similar conversions exist for any null pointer constant, which includes values of type std::nullptr_t as well as the macro NULL.

Example

Demonstrates how nullptr allows forwarding via a template function.

Run this code

#include <cstddef>
#include <iostream>

template<class F, class A>
void Fwd(F f, A a)
{
    f(a);
}

void g(int* i)
{
    std::cout << "Function g called\n";
}

int main()
{
    g(NULL);           // Fine
    g(0);              // Fine

    Fwd(g, nullptr);   // Fine
//  Fwd(g, NULL);  // ERROR: No function g(int)
}

Output:

Function g called
Function g called
Function g called

Keywords

nullptr

See also

NULL	implementation-defined null pointer constant (macro constant)
nullptr_t (C++11)	the type of the null pointer literal nullptr (typedef)

References

• C++11 standard (ISO/IEC 14882:2011):

• 4.10 Pointer conversions [conv.ptr]