c++11 what is 0, NULL and nullptr?

nullptr.cpp

#include <iostream>


void whatis(int*& pointer);


int main()
{
	int* isempty;
	int* zero = 0;
	int* null = NULL;
	int* nullpointer = nullptr;

	std::cout << "isempty:" << std::endl;
	whatis(isempty);

	std::cout << "zero:" << std::endl;
	whatis(zero);

	std::cout << "null:" << std::endl;
	whatis(null);

	std::cout << "nullpointer:" << std::endl;
	whatis(nullpointer);

	std::cin.get();
	return 0;
}

void whatis(int*& pointer)
{
	if (pointer == 0) {
		std::cout << "\t 0" << std::endl;
	}
	
	if (pointer == NULL) {
		std::cout << "\t NULL" << std::endl;
	}

	if (pointer == nullptr) {
		std::cout << "\t nullptr" << std::endl;
	}
}

I tried this and all three of them came out to equal all three? WTF?

This code snippet is not written in C11, but written in C++11. Not the same language. file should be named nullptr.c instead of nullptr.cpp. GCC detects that file extension difference and uses a different compiler under the hood (cc1 instead of cc1plus). Also, you can't use <iostream> because that doesn't exist in C. when compiling this snippet using gcc or clang, make sure you add the -std=c11 flag to enable c11. Otherwise, it would default to c99, which is the previous ansi standard. If I recall correctly, nullptr doesn't even exist in C. You have to use NULL, which should be a defined as ((void*)0).