1

我有一个UtlString类，它派生自std::string并添加了额外的实用程序，例如将 int 转换为字符串。但是当我在下面的代码中将这个类与流一起使用时，我遇到了一些错误

istream& operator >> (istream& stream, UtlDatePeriod& object)
{

  stream >> (object._startDate).AsString() >> (object._endDate).AsString();
//(object._startDate).AsString() returns UtlString by value.
  return stream;


}

错误是：

error: no match for âoperator>>â in âstream >> std::basic_string<char, std::char_traits<char>, std::allocator<char> >(((const std::basic_string<char, std::char_traits<char>, std::allocator<char> >&)((const std::basic_string<char, std::char_traits<char>, std::allocator<char> >*)(& jda::UtlDate::AsString() const().jda::UtlString::<anonymous>))))â

/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/istream:119: note: candidates are: 
std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_istream<_CharT, _Traits>& (*)(std::basic_istream<_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/istream:123: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:130: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:166: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:170: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:173: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:177: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:180: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:184: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:188: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:193: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:197: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:202: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:206: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:210: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_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/istream:214: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(void*&) [with _CharT = char, _Traits = std::char_traits<char>]

/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../include/c++/4.4.6/istream:238: note:                 std::basic_istream<_CharT, _Traits>& std::basic_istream<_CharT, _Traits>::operator>>(std::basic_streambuf<_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/bits/basic_string.h:2485: note:                 std::basic_istream<_CharT, _Traits>& std::operator>>(std::basic_istream<_CharT, _Traits>&, std::basic_string<_CharT, _Traits, _Alloc>&) [with _CharT = char, _Traits = std::char_traits<char>, _Alloc = std::allocator<char>]
4

3 回答 3

3

不要使用继承来添加额外的实用程序。相反，添加非成员函数以将该功能提供给std::string. 所以而不是

class FancyString: public std::string
{
public:
     void doCoolStuff() const;
};

写

void doCoolStuff(std::string const& s);

如果您（也）需要向 a 添加额外的状态std::string，请使用组合

class FancyString
{
public: 
     void doCoolStuff() const;
private:
     int some_state;
     std::string s_;
};

std::string从未设计为基类。一方面，它没有虚拟析构函数。

于 2013-09-24T14:20:52.103 回答
2

你的代码是：

stream >> (object._startDate).AsString() ...

为了澄清您的问题，请参阅下面的错误代码：

string f()
{
   return "Hi";
}

...

cin >> f(); // <--- ERROR

该对象cin需要对左值的非常量引用，string但没有这样的事情。

于 2013-09-24T14:23:45.393 回答
0

如果您确实想从 istream 中读取新课程，则应添加功能

istream & operator >> (istream & is, Uistream&  data);
于 2013-09-24T14:24:53.143 回答