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>.

Quick API 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 pointer-to-member type	Converts to a null pointer-to-member 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);        // 调用 f(int)，可能非预期
    f(nullptr);  // 调用 f(int*)，精确匹配
    int* p = nullptr;
    if (p == nullptr) { std::cout << "null\n"; }
}

Embedded Applicability: High

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

Compiler Support

GCC	Clang	MSVC
4.6	3.0	2010

See Also

• cppreference: nullptr

---

Some content referenced from cppreference.com, licensed under CC-BY-SA 4.0