typedef typeof(nullptr) nullptr_t;
(since C23)nullptr_t is the type of the predefined null pointer constant, nullptr. It is a distinct type that is not itself a pointer type. It can be implicitly converted to any pointer type or bool, and the result is the null pointer value of that type or false respectively. No type other than nullptr_t itself can be converted or explicitly cast to nullptr_t.
sizeof(nullptr_t) and alignof(nullptr_t) are equal to sizeof(void*) and alignof(void*) respectively.
nullptr_t has only one valid value, i.e., nullptr. The object representation of nullptr is same as that of (void*)0. If an lvalue conversion produces a nullptr_t value with a different object representation, the behavior is undefined.
Demonstrate that nullptr_t is a distinct type.
#include <stddef.h>
#include <stdio.h>
#define DETECT_NULL_POINTER_CONSTANT(e) \
_Generic(e, \
void* : puts("void*"), \
nullptr_t : puts("nullptr_t"), \
default : puts("other") \
)
int main()
{
DETECT_NULL_POINTER_CONSTANT(((void*)0));
DETECT_NULL_POINTER_CONSTANT(0);
DETECT_NULL_POINTER_CONSTANT(nullptr);
}
Output:
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