Predefined null pointer constant (since C23)

#include <stddef.h>
#include <stdio.h>
void g(int*)
{
    puts("Function g called");
}
#define DETECT_NULL_POINTER_CONSTANT(e) \
    _Generic(e,                         \
        void* : puts("void*"),          \
        nullptr_t : puts("nullptr_t"),  \
        default : puts("integer")       \
    )
int main()
{
    g(nullptr); // OK
    g(NULL); // OK
    g(0); // OK
    auto cloned_nullptr = nullptr;
    g(cloned_nullptr); // OK
    [[maybe_unused]] auto cloned_NULL = NULL;
//  g(cloned_NULL); // 由实现定义：可能通过
    [[maybe_unused]] auto cloned_zero = 0;
//  g(cloned_zero); // 错误
    DETECT_NULL_POINTER_CONSTANT(((void*)0));
    DETECT_NULL_POINTER_CONSTANT(0);
    DETECT_NULL_POINTER_CONSTANT(nullptr);
    DETECT_NULL_POINTER_CONSTANT(NULL); // 由实现定义
}