Question

我在这个问题上进行了大量搜索，发现了许多类似的问题，但我还没有找到解决方案。我正在宣布上课：

class File {

    public:
            string fileName;
            std::ifstream & flinstream;
            Password pass;
            //Next block to look at
            unsigned int nb;
            unsigned int sectorsLeft;
File (string name,string passd);
File ( );
};

和相应的功能：

File::File (string name,string passd) {
         fileName =  name;
        const char* cstr =  name.c_str();
         pass =  Password(passd);
         flinstream =  std::ifstream(cstr);
        if(!flinstream.good()) {
            string err =  "The file '";
            err.append(name);
            err.append("' could not be opened!");
            callError(err,3);
        }
    }

在编译时，我收到以下错误：

 [0] => out.cpp: In constructor ‘File::File(std::string, std::string)’:
    [1] => out.cpp:130:3: error: uninitialized reference member ‘File::flinstream’
    [2] => In file included from /usr/include/c++/4.5/ios:39:0,
    [3] =>                  from /usr/include/c++/4.5/ostream:40,
    [4] =>                  from /usr/include/c++/4.5/iostream:40,
    [5] =>                  from out.cpp:1:
    [6] => /usr/include/c++/4.5/bits/ios_base.h: In member function ‘std::basic_ios<char>& std::basic_ios<char>::operator=(const std::basic_ios<char>&)’:
    [7] => /usr/include/c++/4.5/bits/ios_base.h:788:5: error: ‘std::ios_base& std::ios_base::operator=(const std::ios_base&)’ is private
    [8] => /usr/include/c++/4.5/iosfwd:77:11: error: within this context
    [9] => /usr/include/c++/4.5/iosfwd: In member function ‘std::basic_istream<char>& std::basic_istream<char>::operator=(const std::basic_istream<char>&)’:
    [10] => /usr/include/c++/4.5/iosfwd:83:11: note: synthesized method ‘std::basic_ios<char>& std::basic_ios<char>::operator=(const std::basic_ios<char>&)’ first required here
    [11] => /usr/include/c++/4.5/iosfwd: In member function ‘std::basic_ifstream<char>& std::basic_ifstream<char>::operator=(const std::basic_ifstream<char>&)’:
    [12] => /usr/include/c++/4.5/iosfwd:111:11: note: synthesized method ‘std::basic_istream<char>& std::basic_istream<char>::operator=(const std::basic_istream<char>&)’ first required here
    [13] => /usr/include/c++/4.5/streambuf: In member function ‘std::basic_filebuf<char>& std::basic_filebuf<char>::operator=(const std::basic_filebuf<char>&)’:
    [14] => /usr/include/c++/4.5/streambuf:781:7: error: ‘std::basic_streambuf<_CharT, _Traits>::__streambuf_type& std::basic_streambuf<_CharT, _Traits>::operator=(const std::basic_streambuf<_CharT, _Traits>::__streambuf_type&) [with _CharT = char, _Traits = std::char_traits<char>, std::basic_streambuf<_CharT, _Traits>::__streambuf_type = std::basic_streambuf<char>]’ is private
    [15] => /usr/include/c++/4.5/iosfwd:108:11: error: within this context
    [16] => /usr/include/c++/4.5/iosfwd: In member function ‘std::basic_ifstream<char>& std::basic_ifstream<char>::operator=(const std::basic_ifstream<char>&)’:
    [17] => /usr/include/c++/4.5/iosfwd:111:11: note: synthesized method ‘std::basic_filebuf<char>& std::basic_filebuf<char>::operator=(const std::basic_filebuf<char>&)’ first required here
    [18] => out.cpp: In constructor ‘File::File(std::string, std::string)’:
    [19] => out.cpp:134:36: note: synthesized method ‘std::basic_ifstream<char>& std::basic_ifstream<char>::operator=(const std::basic_ifstream<char>&)’ first required here
    [20] => out.cpp: In constructor ‘File::File()’:
    [21] => out.cpp:142:3: error: uninitialized reference member ‘File::flinstream’
    [22] => out.cpp: In member function ‘File& File::operator=(const File&)’:
    [23] => out.cpp:51:12: error: non-static reference member ‘std::ifstream& File::flinstream’, can't use default assignment operator
    [24] => out.cpp: In function ‘int main(int, char**)’:
    [25] => out.cpp:166:57: note: synthesized method ‘File& File::operator=(const File&)’ first required here
)

我认为ifstream对作业而言非常特别，但是我不知道如何将它包含在课堂中。在此先感谢您的帮助！

编辑：我已尝试过上述类的几种排列，例如使用正常变量：

std::ifstream flinstream;

使用建议的open()功能：

flinstream.open(cstr);

但是，错误仍然相同。

Answer 1

对于初学者，除非您真的想要引用到ifstream，否则我只会在您的班级中声明ifstream

std::ifstream flinstream;

在C ++ 03（以前版本的C ++）中，对流类禁用赋值，因此该行

flinstream =  std::ifstream(cstr);

不会编译。但是，您可以使用std::ifstream::open方法执行此操作：

flinstream.open(cstr);
/* ... remaining processing ... */

希望这有帮助！

Answer 2

参考文献不能保持未初始化状态。您必须初始化初始化列表中的所有引用成员。

flinstream正在构造函数的主体中初始化。在构造函数的主体执行时，flinstream的值必须具有合法值。参考文献必须始终具有合法价值。

初始化程序列表应始终优先于构造函数体。

类错误中的C ++ ifstream

2 个答案: