nullptr, the pointer literal (since C++11)
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[edit] Syntax
nullptr
[edit] 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 .
[edit] Keywords
[edit] 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
[edit] References
- C++23 standard (ISO/IEC 14882:2024):
- 7.3.12 Pointer conversions [conv.ptr]
- C++20 standard (ISO/IEC 14882:2020):
- 7.3.12 Pointer conversions [conv.ptr]
- C++17 standard (ISO/IEC 14882:2017):
- 7.11 Pointer conversions [conv.ptr]
- C++14 standard (ISO/IEC 14882:2014):
- 4.10 Pointer conversions [conv.ptr]
- C++11 standard (ISO/IEC 14882:2011):
- 4.10 Pointer conversions [conv.ptr]
[edit] See also
C documentation for nullptr