1

即使 << 运算符为下面的地图重载，我也遇到了一个非常奇怪的错误，Feature.h 由名为 Session.C 的类使用，我正在尝试使用 << 打印地图 tKeyboard 的值。我对这一切都很陌生，这是一个非常古老的代码，我对这个问题感到困惑，你们能提出一些建议吗？欣赏谢谢。

特征.h

class Feature {
..
public:

 typedef map<string,KeyStroke,std::less<string>,std::allocator<std::pair<const string, KeyStroke> > > tKeyboard;
                               // It is a map of keys
                               // key is the name of the keystroke
      typedef  tKeyboard::const_iterator cKeysIter;
      typedef  tKeyboard::iterator KeysIter;
..
  private:
  friend ostream &operator<<(ostream &os,const tKeyboard &);
..
};

特征.C

ostream &operator<<(ostream &os,const Feature::tKeyboard &k)
{
    os <<" Keyboard >\n";
    for (Feature::cKeysIter i=k.begin() ; i!= k.end() ; i++)
    {
        os << "key name:"<<(*i).first << " ="<< (*i).second ;
    }
    return os;
}

会话.C

 if (keyStrokeVal.empty()){
       Traced(3)<<"sendKey:Error, key "<<keyname<<" not defined or empty\n";
       Traced(7)<<"Printing Feature "<<mCurrentFeature->get_mName() <<" 's keyboard \n" << mCurrentFeature->get_mKeyboard();
       Traced(7)<<"\n";
       return(-1);
    }

错误：

Session.C:541: error: no match for âoperator<<â in âstd::operator<< [with _Traits = std::char_traits<char>](((std::basic_ostream<char, std::char_traits<char> >&)((std::basic_ostream<char, std::char_traits<char> >*)std::operator<< [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>](((std::basic_ostream<char, std::char_traits<char> >&)((std::basic_ostream<char, std::char_traits<char> >*)std::operator<< [with _Traits = std::char_traits<char>](((std::basic_ostream<char, std::char_traits<char> >&)((std::basic_ostream<char, std::char_traits<char> >*)((std::basic_ostream<char, std::char_traits<char> >*)std::operator<< [with _Traits = std::char_traits<char>](((std::basic_ostream<char, std::char_traits<char> >&)((std::basic_ostream<char, std::char_traits<char> >*)((std::basic_ostream<char, std::char_traits<char> >*)std::operator<< [with _Traits = std::char_traits<char>](((std::basic_ostream<char, std::char_traits<char> >&)((std::basic_ostream<char, std::char_traits<char> >*)std::operator<< [with _Traits = std::char_traits<char>](((std::basic_ostream<char, std::char_traits<char> >&)((std::basic_ostream<char, std::char_traits<char> >*)((std::ostream*)LogMgr::traceRovr())->std::basic_ostream<_CharT, _Traits>::operator<< [with _CharT = char, _Traits = std::char_traits<char>](std::endl [with _CharT = char, _Traits = std::char_traits<char>]))), ((const char*)"Session.C")))), ((const char*)" ")))->std::basic_ostream<_CharT, _Traits>::operator<< [with _CharT = char, _Traits = std::char_traits<char>](541))), ((const char*)" - ")))->std::basic_ostream<_CharT, _Traits>::operator<< [with _CharT = char, _Traits = std::char_traits<char>](out_time))), ((const char*)"Printing Feature ")))), ((const std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)((const std::string*)((Session*)this)->Session::mCurrentFeature->Feature::get_mName()))))), ((const char*)" \'s keyboard \012")) << ((Session*)this)->Session::mCurrentFeature->Feature::get_mKeyboard()â
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:108: note: candidates are: std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ostream<_CharT, _Traits>& (*)(std::basic_ostream<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:117: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_ios<_CharT, _Traits>& (*)(std::basic_ios<_CharT, _Traits>&)) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:127: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::ios_base& (*)(std::ios_base&)) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:165: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:169: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:173: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(bool) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/ostream.tcc:91: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:180: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(short unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/ostream.tcc:105: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:191: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:200: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:204: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long long unsigned int) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:209: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(double) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:213: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(float) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:221: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(long double) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/ostream:225: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(const void*) [with _CharT = char, _Traits = std::char_traits<char>]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/ostream.tcc:119: note:                 std::basic_ostream<_CharT, _Traits>& std::basic_ostream<_CharT, _Traits>::operator<<(std::basic_streambuf<_CharT, _Traits>*) [with _CharT = char, _Traits = std::char_traits<char>]
4

3 回答 3

1

问题是，如果friend声明首先声明（但未定义）一个函数，则该函数的名称不会被引入周围的范围。引用 C++11，[namespace.memdef]§3：

如果friend非本地类中的声明首先声明了一个类或函数，则友元类或函数是最内层封闭命名空间的成员。在该命名空间范围内（在授予友谊的类定义之前或之后）提供匹配声明之前，未限定查找 (3.4.1) 或限定查找 (3.4.3) 无法找到朋友的名称。如果调用友元函数，则可以通过名称查找找到其名称，该名称查找考虑来自与函数参数类型相关联的命名空间和类的函数（3.4.2）。

（强调我的）

因此，解决方案是一个单独的类外声明：

std::ostream &operator<<(std::ostream &os,const Feature::tKeyboard &);
于 2013-09-12T07:58:40.970 回答
0

一个可能的原因是::operator<<由于未搜索全局命名空间，因此未找到您的。而且您不允许将您的添加operator<<到::std::. 如果是这种情况，可以使用本地using ::operator<<.

于 2013-09-12T07:39:05.717 回答
-2

您是否尝试将输出运算符添加到命名空间 std 以帮助 ADL？

namespace std{
ostream &operator<<(ostream &os,const Feature::tKeyboard &k)
{
  os <<" Keyboard >\n";
  for (Feature::cKeysIter i=k.begin() ; i!= k.end() ; i++)
  {
    os << "key name:"<<(*i).first << " ="<< (*i).second ;
  }
  return os;
}
}
于 2013-09-12T07:12:10.260 回答