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Defined in header <clocale> | ||
Defined in header <cstddef> | ||
Defined in header <cstdio> | ||
Defined in header <cstdlib> | ||
Defined in header <cstring> | ||
Defined in header <ctime> | ||
Defined in header <cwchar> | ||
#define NULL /* implementation-defined */ | ||
The macroNULL is an implementation-definednull pointer constant.
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#define NULL 0// since C++11#define NULL nullptr |
In C, the macroNULL may have the typevoid*, but that is not allowed in C++ because null pointer constants cannot have that type.
#include <cstddef>#include <iostream>#include <type_traits>#include <typeinfo> 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;auto nullvar= NULL;// may trigger a warning when compiling with gcc/clang std::cout<<"The type of nullvar is "<<typeid(nullvar).name()<<'\n'; ifconstexpr(std::is_same_v<decltype(NULL),std::nullptr_t>)std::cout<<"NULL implemented with type std::nullptr_t\n";elsestd::cout<<"NULL implemented using an integral type\n"; [](...){}(p, p2, f, mp, mfp);// < suppresses "unused variable" warnings}
Possible output:
The type of nullvar is longNULL implemented using an integral type
| nullptr(C++11) | the pointer literal which specifies a null pointer value[edit] |
(C++11) | the type of the null pointer literalnullptr (typedef)[edit] |
C documentation forNULL | |
