如何强制xcode使用正确的iostream标头c

xcode 4.2
os x 10.7

当我设置我的包括看起来像：

#include <iostream>
#include <boost/thread.hpp>

我从位于/ opt / local / include / boost / tr1 / tr1的文件中收到以下错误

Lexical or Preprocessor Issue
'boost/tr1/detail/config_all.hpp' file not found

/ opt / local / include / boost / tr1 / tr1 / iostream文件的内容：

//  (C) Copyright John Maddock 2005.
//  Use,modification and diStribution are subject to the
//  Boost Software License,Version 1.0. (See accompanying file
//  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
//  This file exists to prevent std lib headers from accidentally
//  including a TR1 extention header; we must suppress this otherwise
//  we can end up with cyclic dependencies with some std lib implementations.
//
#ifndef BOOST_TR1_iostream_INCLUDED
#  define BOOST_TR1_iostream_INCLUDED
#  ifndef BOOST_TR1_NO_REcursION
#     define BOOST_TR1_NO_REcursION
#     define BOOST_TR1_NO_iostream_REcursION
#  endif
#  include <boost/tr1/detail/config_all.hpp>
#  if Defined(BOOST_HAS_INCLUDE_NEXT) && !defined(BOOST_TR1_DISABLE_INCLUDE_NEXT)
#     include_next <iostream>
#  else
#     include BOOST_TR1_STD_HEADER(iostream)
#  endif
#  ifdef BOOST_TR1_NO_iostream_REcursION
#     undef BOOST_TR1_NO_iostream_REcursION
#     undef BOOST_TR1_NO_REcursION
#  endif
#endif

@R_400_10675@用位于/Developer/SDKs/MacOSX10.7.sdk/usr/include/c /4.2.1/的iostream标头

你将不得不原谅我,因为我对c很新,甚至更新xcode.预先感谢您的任何帮助.