Thread: What Is this???

#include <stddef.h>

I have never seen this before. When I was using C++ in the past this never came up, I can't compile with this error.

Why is it not allowing me to compile a simple code then?

Code:

// -*- C++ -*- forwarding header.
// Copyright (C) 1997, 1998, 1999, 2000, 2002 Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

//
// ISO C++ 14882: 18.1  Types
//

/** @file cstddef
 *  This is a Standard C++ Library file.  You should @c #include this file
 *  in your programs, rather than any of the "*.h" implementation files.
 *
 *  This is the C++ version of the Standard C Library header @c stddef.h,
 *  and its contents are (mostly) the same as that header, but are all
 *  contained in the namespace @c std.
 */

#ifndef _CPP_CSTDDEF
#define _CPP_CSTDDEF 1

#pragma GCC system_header

#include <stddef.h>

namespace std 
{
  using ::ptrdiff_t;
  using ::size_t;
}

#endif