nullptr (C++11)

In a Nutshell

A null pointer literal of type std::nullptr_t that safely distinguishes integer overloads, completely resolving the ambiguity the NULL macro and the integer 0 create in templates and function overloading.

Header

No header required (it is a language keyword); the type is defined in <cstddef>.

Core API Quick Reference

Operation	Signature	Description
Null pointer literal	nullptr	A prvalue of type std::nullptr_t
Implicit conversion	→ any pointer type	Converts to the null pointer value of the corresponding type
Implicit conversion	→ any member pointer type	Converts to the null member pointer value of the corresponding type

Minimal Example

#include <iostream>
void f(int) { std::cout << "int\n"; }
void f(int*) { std::cout << "int*\n"; }

int main() {
    f(0);        // Calls f(int), possibly unintended
    f(nullptr);  // Calls f(int*), exact match
    int* p = nullptr;
    if (p == nullptr) { std::cout << "null\n"; }
}

Embedded Applicability: High

• A zero-overhead abstraction: the compiler directly produces a null pointer value at compile time, generating the same instructions as 0 or NULL
• Avoids integer-vs-pointer overload ambiguity in register-manipulation functions (e.g., overloads that operate on hardware registers)
• Behaves correctly in template metaprogramming (e.g., static assertions, type traits), where NULL and 0 would fail
• Fully compatible with C-style low-level hardware-manipulation code, so NULL can be replaced incrementally with no risk

Compiler Support

GCC	Clang	MSVC
4.6	3.0	2010

See Also

• cppreference: nullptr

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