C++中cout函数的理解

一、test.cpp

include 
  
   
using namespace std;
int main()
{
     cout<<"hello"<
   
    
 
    
二、iostream位于/usr/include/c++/4.4，代码如下：
 
    





 
    
// Standard iostream objects -*- C++ -*-

// Copyright (C) 1997, 1998, 1999, 2001, 2002, 2005, 2008, 2009
// 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 3, 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.

// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// 
     .

/** @file iostream
 *  This is a Standard C++ Library header. 
 */

//
// ISO C++ 14882: 27.3  Standard iostream objects
//

#ifndef _GLIBCXX_IOSTREAM
#define _GLIBCXX_IOSTREAM 1

#pragma GCC system_header

#include 
     
      
#include 
      
        #include 
       
         _GLIBCXX_BEGIN_NAMESPACE(std)//namespace { /** * @name Standard Stream Objects * * The 
        
          header declares the eight 
         standard stream * objects. For other declarations, see * http://gcc.gnu.org/onlinedocs/libstdc++/manual/bk01pt11ch24.
         html * and the @link iosfwd I/O forward declarations @endlink * * They are required by default to cooperate with the global C library's * @c FILE streams, and to be available during program startup and * termination. For more information, see the HOWTO linked to above. */ //@{ extern istream cin; ///< Linked to standard input extern ostream cout; ///< Linked to standard output extern ostream cerr; ///< Linked to standard error (unbuffered) extern ostream clog; ///< Linked to standard error (buffered) #ifdef _GLIBCXX_USE_WCHAR_T extern wistream wcin; ///< Linked to standard input extern wostream wcout; ///< Linked to standard output extern wostream wcerr; ///< Linked to standard error (unbuffered) extern wostream wclog; ///< Linked to standard error (buffered) #endif //@} // For construction of filebuffers for cout, cin, cerr, clog et. al. static ios_base::Init __ioinit; _GLIBCXX_END_NAMESPACE } #endif /* _GLIBCXX_
         IOSTREAM */
        
       
      
     
 
    
 
    

 
 说明cout是类ostream的实例，并且位于std这个命名空间下，所以要using namespace std; 
    
 cout<<是ostream类的运算符重载