C++ 无法将派生字符串类与ifstream类一起使用

我有一个

UtlString

类，它派生自

std:：string

，并添加了额外的实用程序，如将int转换为string。但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>]

error:std:：basic_string（（（const std:：basic_string&）（（const std:：basic_string*）（&jda:：UtlDate:：AsString（）const（）.jda:：UtlString:：））中的–operator>>不匹配
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../../include/c++/4.4.6/istream:119：注：候选者包括：
std:：basic_-istream&std:：basic_-istream:：operator>>（std:：basic_-istream&（*）（std:：basic_-istream&））[带_-CharT=char，_-Traits=std:：char\u-Traits]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../include/c++/4.4.6/istream:123：注意：std:：basic_-istream&std:：basic_-istream:：operator>>（std:：basic_-ios&（*）（std:：basic_-ios&）[带.\u-CharT=CharT，\u-Traits=std:：CharT]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../include/c++/4.4.6/istream:130：注：std:：basic_-istStream&std:：basic_-istStream&std:：basic_-Stream:：operator>>（std:：ios\u-base&（*）（std:：ios\u-base&）[带.\u-CharT=CharT，\u-Traits=std:：CharT]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../include/c++/4.4.6/istream:166：注意：std:：basic_istream&std:：basic_istream:：operator>>（bool&）[带_CharT=char，_Traits=std:：char_Traits]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../include/c++/4.4.6/istream:170：注意：std:：basic_istream&std:：basic_istream:：operator>>（短int&）[带_CharT=char，_Traits=std:：char\u Traits]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../include/c++/4.4.6/istream:173:注意：std:：basic_istream&std:：basic_istream:：operator>>（短的无符号int&）[带_CharT=CharT，_Traits=std:：char
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../include/c++/4.4.6/istream:177：注意：std:：basic_istream&std:：basic_istream:：operator>>（int&）[带_CharT=char，_Traits=std:：char_Traits]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../include/c++/4.4.6/istream:180：注意：std:：basic_istream&std:：basic_istream:：operator>>（无符号int&）[带_CharT=char，_Traits=std:：char_Traits]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../include/c++/4.4.6/istream:184：注意：std:：basic_istream&std:：basic_istream:：operator>>（长整型）[带_CharT=char，_Traits=std:：char_Traits]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../include/c++/4.4.6/istream:188：注意：std:：basic_istream&std:：basic_istream:：operator>>（长无符号int&）[带_CharT=CharT，_Traits=std:：char
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../../include/c++/4.4.6/istream:193：注意：std:：basic_istream&std:：basic_istream:：operator>>（long long int&）[带_CharT=CharT，_Traits=std:：char_Traits]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../include/c++/4.4.6/istream:197:注意：std:：basic_istream&std:：basic_istream:：operator>>（长-长无符号int&）[带_CharT=CharT，_Traits=std:：char
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../include/c++/4.4.6/istream:202：注意：std:：basic_istream&std:：basic_istream:：operator>>（float&）[带_CharT=char，_Traits=std:：char_Traits]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../include/c++/4.4.6/istream:206：注意：std:：basic_-istream&std:：basic_-istream:：operator>>（double&）[带_-CharT=char，_-Traits=std:：char\u-Traits]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../include/c++/4.4.6/istream:210：注意：std:：basic_istream&std:：basic_istream:：operator>>（长双精度&）[带_CharT=CharT，_Traits=std:：char\u Traits]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../include/c++/4.4.6/istream:214:注意：std:：basic_istream&std:：basic_istream:：operator>>（void*&）[带_CharT=char，_Traits=std:：char
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../../include/c++/4.4.6/istream:238：注：std:：basic_istream&std:：basic_istream:：operator>>（std:：basic_streambuf*）[带_CharT=char，_Traits=std:：char_Traits]
/usr/lib/gcc/x86_64-redhat-linux/4.4.6/../../../../../../../../include/c++/4.4.6/bits/basic_string.h:2485：注意：std:：basic_istream&std:：operator>>（std:：basic_istream&，std:：basic_string&），std:：basic_string&[带(CharT=CharT，)Traits=std:：CharT\u-Alloc=std:：分配器]

不要使用继承来添加额外的实用程序。相反，添加非成员函数以向

std:：string

提供该功能。所以不是

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

写

如果您（还）需要向

std:：string

添加额外的状态，请使用composition

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

---

std:：string

从未被设计为基类。首先，它没有虚拟析构函数。

不要使用继承来添加额外的实用程序。相反，添加非成员函数以向

std:：string

提供该功能。所以不是

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

写

如果您（还）需要向

std:：string

添加额外的状态，请使用composition

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

std:：string

从未被设计为基类。首先，它没有虚拟析构函数。

您的代码是：

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

要澄清您的问题，请参阅以下错误代码：

string f()
{
   return "Hi";
}

...

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

string f（）
{
返回“Hi”；
}
...
cin>>f（）；// 您的代码是：

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

要澄清您的问题，请参阅以下错误代码：

string f()
{
   return "Hi";
}

...

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

string f（）
{
返回“Hi”；
}
...
cin>>f（）；// 如果您确实希望从istream读取新类，则应该添加函数

istream & operator >> (istream & is, Uistream&  data);

如果您确实希望从istream读取新类，则应该添加函数

istream & operator >> (istream & is, Uistream&  data);

从
std:：string
派生是一种糟糕的方法。我认为使用组合而不是继承会使您的问题更容易解决。从
std:：string
派生是一种糟糕的方法。我认为使用构图而不是在