| Defined in header <cstddef> | ||
|---|---|---|
| Defined in header <cstring> | ||
| Defined in header <cwchar> | ||
| Defined in header <ctime> | ||
| Defined in header <cstdio> | (until C++11) | |
| Defined in header <clocale> | (since C++11) | |
| Defined in header <cstdlib> | (since C++11) | |
#define NULL /*implementation-defined*/ |
The macro NULL is an implementation-defined null pointer constant, which may be.
| an integral constant expression rvalue of integer type that evaluates to zero. | (until C++11) |
| an integral constant expression prvalue of integer type that evaluates to zero or a prvalue of type | (since C++11) (until C++14) |
| an integer literal with value zero, or a prvalue of type | (since C++14) |
A null pointer constant may be implicitly converted to any pointer type; such conversion results in the null pointer value of that type. If a null pointer constant has integer type, it may be converted to a prvalue of type std::nullptr_t.
Possible implementation
#define NULL 0 //since C++11 #define NULL nullptr |
Notes
In C, the macro NULL may have the type void*, but that is not allowed in C++.
Example
#include <cstddef>
class S;
int main()
{
int* p = NULL;
int* p2 = static_cast<std::nullptr_t>(NULL);
void(*f)(int) = NULL;
int S::*mp = NULL;
void(S::*mfp)(int) = NULL;
}See also
| nullptr | the pointer literal which specifies a null pointer value (C++11) |
| (C++11) | the type of the null pointer literal nullptr (typedef) |
C documentation for NULL | |
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