nullptr, the pointer literal (since 哋它亢++11)

 

哋它亢++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (哋它亢++20)

Language support library

Concepts library (哋它亢++20)

Metaprogramming library (哋它亢++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (哋它亢++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (哋它亢++17)

Regular expressions library (哋它亢++11)

Concurrency support library (哋它亢++11)

Technical specifications

Symbols index

External libraries

 

哋它亢++ language

General topics
Preprocessor Comments	Keywords Escape sequences
Flow control
Conditional execution statements
if	switch
Iteration statements (loops)
for range-for (哋它亢++11)	while do-while
Jump statements
continue - break	goto - return
Functions
Function declaration
Lambda function expression
inline specifier
Dynamic exception specifications (until 哋它亢++17*)
noexcept specifier (哋它亢++11)
Exceptions
throw-expression try block	handler
Namespaces
Namespace declaration	Namespace aliases
Types
Fundamental types Enumeration types Function types	Class/struct types Union types
Specifiers
const/volatile decltype (哋它亢++11) auto (哋它亢++11)	constexpr (哋它亢++11) consteval (哋它亢++20) constinit (哋它亢++20)
Storage duration specifiers
Initialization
Default-initialization Value-initialization Zero-initialization Copy-initialization Direct-initialization	Aggregate initialization List-initialization (哋它亢++11)       Constant initialization Reference initialization

Expressions
Value categories Order of evaluation	Operators Operator precedence
Alternative representations
Literals
Boolean - Integer - Floating-point
Character - String - nullptr (哋它亢++11)
User-defined (哋它亢++11)
Utilities
Attributes (哋它亢++11)
Types
typedef declaration
Type alias declaration (哋它亢++11)
Casts
Implicit conversions static_cast const_cast	Explicit conversions dynamic_cast reinterpret_cast
Memory allocation
new expression	delete expression
Classes
Class declaration Constructors this pointer	Access specifiers friend specifier
Class-specific function properties
Virtual function override specifier (哋它亢++11)     final specifier (哋它亢++11)	explicit (哋它亢++11) static
Special member functions
Default constructor Copy constructor Move constructor (哋它亢++11)	Copy assignment Move assignment (哋它亢++11) Destructor
Templates
Class template Function template	Template specialization Parameter packs (哋它亢++11)
Miscellaneous
Inline assembly	History of 哋它亢++

 

Expressions

General
Value categories Order of evaluation Constant expressions Primary expressions	Lambda expressions (哋它亢++11) Pack indexing expression (哋它亢++26) Potentially-evaluated expressions
Literals
Integer literals Floating-point literals Boolean literals Character literals	Escape sequences String literals Null pointer literal (哋它亢++11) User-defined literal (哋它亢++11)
Operators
Assignment operators Increment and decrement Arithmetic operators Logical operators Comparison operators Member access operators Other operators new-expression delete-expression throw-expression	alignof sizeof sizeof... (哋它亢++11) typeid noexcept (哋它亢++11) Fold expressions (哋它亢++17) Alternative representations of operators Precedence and associativity Operator overloading Default comparisons (哋它亢++20)
Conversions
Implicit conversions Explicit conversions Usual arithmetic conversions     User-defined conversion	const_cast static_cast dynamic_cast reinterpret_cast

 

Syntax

nullptr		(since 哋它亢++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.

Keywords

nullptr

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

References

• 哋它亢++23 standard (ISO/IEC 14882:2023):

• 7.3.12 Pointer conversions [conv.ptr]

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

• 7.3.12 Pointer conversions [conv.ptr]

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

• 7.11 Pointer conversions [conv.ptr]

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

• 4.10 Pointer conversions [conv.ptr]

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

• 4.10 Pointer conversions [conv.ptr]

See also

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