nullptr, the pointer literal

 

C++

Language

Standard library headers

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Technical Specifications

 

C++ language

 

Expressions

General

value categories (lvalue, rvalue, xvalue)

order of evaluation (sequence points)

constant expressions

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primary expressions

lambda-expression(C++11)

Literals

integer literals

floating-point literals

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string literals

null pointer literal(C++11)

user-defined literal(C++11)

Operators

Assignment operators: a=b, a+=b, a-=b, a*=b, a/=b, a%=b, a&=b, a|=b, a^=b, a<<=b, a>>=

Increment and decrement: ++a, --a, a++, a--

Arithmetic operators: +a, -a, a+b, a-b, a*b, a/b, a%b, ~a, a&b, a|b, a^b, a<<b, a>>b

Logical operators: a||b, a&&b, !a

Comparison operators: a==b, a!=b, a<b, a>b, a<=b, a>=b

Member access operators: a[b], *a, &a, a->b, a.b, a->*b, a.*b

Other operators: a(...), a,b, a?b:c

Alternative representations of operators

Precedence and associativity

Fold expression(C++17)

new-expression

delete-expression

throw-expression

alignof

sizeof

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typeid

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Operator overloading

Conversions

Implicit conversions

const_cast

static_cast

reinterpret_cast

dynamic_cast

Explicit conversions (T)a, T(a)

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]