NULL
From cppreference.com
Defined in header
<cstddef>
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Defined in header
<cstring>
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Defined in header
<cwchar>
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Defined in header
<ctime>
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Defined in header
<cstdio>
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(until C++11) |
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Defined in header
<clocale>
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(since C++11) |
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Defined in header
<cstdlib>
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(since C++11) |
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#define NULL /*implementation-defined*/
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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 std::nullptr_t |
(since C++11) (until C++14) |
an integer literal with value zero, or a prvalue of type std::nullptr_t |
(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.
Contents |
[edit] Possible implementation
#define NULL 0 //since C++11 #define NULL nullptr |
[edit] Notes
In C, the macro NULL
may have the type void*
, but that is not allowed in C++.
[edit] Example
Run this code
#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; }
[edit] See also
nullptr | the pointer literal which specifies a null pointer value (C++11) |
(C++11)
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the type of the null pointer literal nullptr (typedef) |
C documentation for NULL
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