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 either, because my attempt to use it is rejected as

error: 'nullptr' was not declared in this scope

score 21 · Accepted Answer · edited May 23 '17 at 11:45

21

GCC 4.4.1 does not support nullptr.

Support for nullptr was added in GCC 4.6.0: http://gcc.gnu.org/gcc-4.6/changes.html

Improved experimental support for the upcoming C++0x ISO C++ standard, including support for nullptr (thanks to Magnus Fromreide), noexcept, unrestricted unions, range-based for loops (thanks to Rodrigo Rivas Costa), implicitly deleted functions and implicit move constructors.

For earlier versions of GCC, if you want to experiment with nullptr you can try the workaround in this SO question:

Can nullptr be emulated in GCC?

edited May 23 '17 at 11:45

Community

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answered Sep 21 '10 at 00:18

ZoogieZork

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since pre GCC 4.6 doesn't have nullptr you can use "__null" – Trevor Boyd Smith Oct 20 '15 at 19:53
1

@Trevor Boyd Smith: `__null` is simply what NULL is defined to on GCC. It is *not* the same as `nullptr`, since it (obviously) has the same semantics as NULL. There is no reason to use `__null`. – rdb Jan 09 '17 at 14:52
Isn't he talking about g++? – Suraj Jain Feb 07 '17 at 11:22

score 3 · Answer 2 · edited Feb 27 '15 at 10:44

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<typename any> operator any * () const
    {
        return 0;
    }
    template<class any, typename T> 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<typename any> void operator +(any) const
    {
        /*I Love MSVC 2005!*/
    }
    template<typename any> void operator -(any) const
    {
        /*I Love MSVC 2005!*/
    }
    };
static const nullptr_t __nullptr = {};
}

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

maybe you should consider also ensuring that the alignment is correct as well, if this is important to you — danielschemmel, May 03 '13 at 04:23
Yaroslav, maybe you should consider writing without shouting. :) — Andrea Lazzarotto, Jul 12 '13 at 15:12

score 2 · Answer 3 · answered Jan 30 '14 at 10:47

2

I use -std=c++0x to enable the nullptr feature with gcc 4.6.3

answered Jan 30 '14 at 10:47

xsj0jsx

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But -std=c++0x does not enable nullptr in Gcc 4.4.x – Fernando Gonzalez Sanchez Jan 13 '16 at 17:46

score 2 · Answer 4 · answered Jul 14 '15 at 05:37

2

If you don't have the latest gcc which supports C++11 , try using NULL instead of nullptr.

answered Jul 14 '15 at 05:37

lppier

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

4 Answers4

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