使用std :: copy - 错误C2679：找不到正确的二进制'='运算符 [英] Using std::copy - error C2679: can't find correct binary '=' operator

问题描述

我尝试使用此问题的解决方案：

• 如何在C ++中逐行迭代cin？
  

错误讯息

c：\program files（x86）\microsoft visual studio 10.0 \vc\include\xutility（2144）：error C2679：binary'='：无操作符，它接受类型为 const Line'（或者没有可接受的转换）

b
$ b

我使用Visual C ++ 2010 Express。

代码

 ＃include< string> 
＃include< iostream> 
＃include< fstream> 
＃include< vector> 
＃include< iterator> 
 
 class Line 
 {
 std :: string data; 
 
 public：
 friend std :: istream& operator>>（std :: istream& inputStream，Line& line）
 {
 std :: getline（inputStream，line.data）; 
 return inputStream; 
} 
 
操作符std :: string（）
 {
返回数据; 
} 
}; 
 
 int main（int argc，char * argv []）
 {
 std :: fstream file（filename.txt，std :: fstream :: in | std :: fstream :: out）; 
 std :: vector< std :: string>线; 
 
 //错误在这些行之一
 std :: copy（
 std :: istream_iterator< Line>（file），
 std :: istream_iterator< Line>（），
 std :: back_inserter（lines））; 
} 
  

解决方案

罚款：

  class Line 
 {
 std :: string data; 
 
 public：
 friend std :: istream& operator>>（std :: istream& inputStream，Line& line）
 {
 std :: getline（inputStream，line.data）; 
 return inputStream; 
} 
 
操作符std :: string（）const 
 {
返回数据; 
} 
}; 
  

转换运算符需要 const 。

I am trying to use a solution from this question:

• How do I iterate over cin line by line in C++?

The error message

c:\program files (x86)\microsoft visual studio 10.0\vc\include\xutility(2144): error C2679: binary '=' : no operator found which takes a right-hand operand of type 'const Line' (or there is no acceptable conversion)

(and a bunch of template trace data after this)

I am using Visual C++ 2010 Express.

The code

#include<string>
#include<iostream>
#include<fstream>
#include<vector>
#include<iterator>

class Line
{
  std::string data;

public:
  friend std::istream& operator>>(std::istream& inputStream, Line& line)
  {
    std::getline(inputStream, line.data);
    return inputStream;
  }

  operator std::string()
  {
    return data;
  }
};

int main(int argc, char* argv[])
{
  std::fstream file("filename.txt", std::fstream::in | std::fstream::out);
  std::vector<std::string> lines;

  // error is in one of these lines
  std::copy(
    std::istream_iterator<Line>(file),
    std::istream_iterator<Line>(),
    std::back_inserter(lines));
}

解决方案

Here is correct version that compiles fine :

class Line
{
    std::string data;

    public:
        friend std::istream& operator>>(std::istream& inputStream, Line& line)
        {
            std::getline(inputStream, line.data);
            return inputStream;
        }

        operator std::string() const
        {
            return data;
        }
};

The conversion operator needs to be const.

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