nullptr, the pointer literal

 

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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 that nullptr retains the meaning of null pointer constant even if it is no longer a literal.

Run this code

#include <cstddef>
#include <iostream>
 
template<class T>
constexpr T clone(const T& t)
{
    return t;
}
 
void g(int*)
{
    std::cout << "Function g called\n";
}
 
int main()
{
    g(nullptr);        // Fine
    g(NULL);           // Fine
    g(0);              // Fine
 
    g(clone(nullptr)); // Fine
//  g(clone(NULL));    // ERROR: non-literal zero cannot be a null pointer constant
//  g(clone(0));       // ERROR: non-literal zero cannot be a null pointer constant
}

Output:

Function g called
Function g called
Function g called
Function g called

Keywords

nullptr

References

• C++20 standard (ISO/IEC 14882:2020):

• 7.3.12 Pointer conversions [conv.ptr]

• C++17 standard (ISO/IEC 14882:2017):

• 7.11 Pointer conversions [conv.ptr]

• C++14 standard (ISO/IEC 14882:2014):

• 4.10 Pointer conversions [conv.ptr]

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

• 4.10 Pointer conversions [conv.ptr]

See also

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