What header file needs to be included for using nullptr in g++?

Question

I am using g++ 4.4.1 and want to use nullptr, but I am not being able to find which header file is required to be included. It does not seem to be keyword eithe

Answer 1

I would recommend not using nullptr as defined above, because it can be dangerous. If you want to use nullptr the following statement should be true.

sizeof(nullptr) == sizeof(void*) == sizeof(any pointer)

However, sizeof(nullptr) (as defined above) will not comply to this rule. It will actually evaluate to sizeof(bad nullptr) = 1.

This is a correct implementation.

#pragma once

namespace std
{
    //based on SC22/WG21/N2431 = J16/07-0301
    struct nullptr_t
    {
        template operator any * () const
    {
        return 0;
    }
    template operator T any:: * () const
    {
        return 0;
    }

#ifdef _MSC_VER
    struct pad {};
    pad __[sizeof(void*)/sizeof(pad)];
#else
    char __[sizeof(void*)];
#endif
private:
    //  nullptr_t();// {}
    //  nullptr_t(const nullptr_t&);
    //  void operator = (const nullptr_t&);
    void operator &() const;
    template void operator +(any) const
    {
        /*I Love MSVC 2005!*/
    }
    template void operator -(any) const
    {
        /*I Love MSVC 2005!*/
    }
    };
static const nullptr_t __nullptr = {};
}

#ifndef nullptr
#define nullptr std::__nullptr
#endif