Question

Nowadays, with C++11, Whats recommended to use, Zero or NULL? The first of the second if?

int * p = getPointer();

if( 0 == p ){
    // something
}

if( NULL == p ){
    // something
}

UPDATE: I forget the new

if( nullptr == p ){
    // something
}

UPDATE 2: the examples are to show the options to write null pointer, I know is more pleasant to write if( !p ).

Answer 1

The other answers are right. But I wanted to say a little more about why nullptr is better.

In C++11 “perfect forwarding” is very important. It is used everywhere. Obvious places are bind and function. But it is also used in a multitude of other places under the covers. But “perfect forwarding” isn’t perfect. And one of the places it fails is null pointer constants.

template <class T>
void display(T)
{
    std::cout << type_name<T>() << '\n';
}

template <class T>
void
f(T&& t)
{
    display(std::forward<T>(t));  // "perfectly forward" T
}

int main()
{
    f(0);
    f(NULL);
    f(nullptr);
}

With an appropriate definition of type_name<T>(), on my system this prints out:

int
long
std::nullptr_t

This can easily make the difference between working code and errors. With any luck your errors will come at compile time (with horrible error messages). But you may also get run time errors in some circumstances.

Aggressively ban use of 0 and NULL in your code.

Even if you’re not perfect forwarding in your code, code you call (such as the std::lib) is very likely using it under the covers.