nullptr (C++11)

In a Nutshell

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

Header

No header required (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 a null pointer value of the corresponding type
Implicit conversion	→ Any member pointer type	Converts to a null member pointer value of the corresponding type

Minimal Example

void f(int* p) {
    // Handle pointer
}

void f(int i) {
    // Handle integer
}

int main() {
    // Calls f(int*)
    f(nullptr);

    // Calls f(int)
    f(0);
}

Embedded Applicability: High

• A zero-overhead abstraction; the compiler directly generates a null pointer value, producing the same instructions as 0 or NULL.
• Avoids ambiguity between integer and pointer overloads in register manipulation functions (e.g., overloads for hardware registers).
• Behaves correctly in template metaprogramming (e.g., static assertions, type traits), whereas NULL and 0 would fail.
• Fully compatible with C-style low-level hardware manipulation code, allowing for risk-free, gradual replacement.

Compiler Support

GCC	Clang	MSVC
4.6	3.0	2010

See Also

• cppreference: nullptr

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