C++ ifstream 类错误

Question

我围绕这个问题进行了很多搜索，发现了很多类似的问题，但我还没有找到解决方案。我正在声明一个类：

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 ( );
};

和一个相应的函数：

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
)

我收集到 ifstream 对赋值和所有内容相当特殊，但我没有想法如何将其包含在课程中。预先感谢您的帮助！

编辑：我已经尝试了上述类的几种排列，例如使用普通变量：

std::ifstream flinstream;

以及使用建议的 open() 函数：

flinstream.open(cstr);

但是，错误仍然相同。

Answer 1

对于初学者，除非您确实想要对 ifstream 的引用，否则我只需在您的类中将 ifstream 声明为

std::ifstream flinstream;

In C++03 (以前版本的 C++），流类的赋值被禁用，因此该行将

flinstream =  std::ifstream(cstr);

无法编译。但是，您可以使用 std::ifstream::open 方法来执行此操作：

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

希望这会有所帮助！

Answer 2

引用不能处于未初始化状态。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。当构造函数主体执行时，flinstream 的值必须具有合法值。参考文献必须始终具有法律价值。

初始值设定项列表应始终优先于构造函数主体。