C ++ 11 / Genrated构造函数 [英] C++11 / Genrated constructor

问题描述

我一直在开发一个由别人（谁离开公司）开始的C ++项目。他写了一段代码，看起来效果很好，但我不明白。

I have been working on a C++ project started by someone else (who left the company). He has written a piece of code which seems to work pretty well but I cannot understand it.

下面是代码的简化版本：

Here is below a simplified version of the code:

有两个类：

class Algo_t {
protected :
    Matrix_t m_Matrix ;
public:
    Algo_t(Matrix_t && Matrix) {
        DoSomething();
    }
};

class Matrix_t {
protected :
    std::ifstream & m_iftsream ;
public:
    Matrix_t(std::ifstream && ifstream) {
        DoSomething();
    }
};

在主要：

在主函数中的以下调用：

There is the following call in the main function:

char * pMyFileName = agrv[1] ;
Algo_t MyAlgo(ifstream(pMyFileName));

首先我很惊讶的是代码编译没有任何错误，因为没有构造函数 Algo_t 以 ifstream 为参数。
我更惊讶地注意到这个代码工作得很好。

First I was very surprised that the code compiled without any error because there is no constructor of Algo_t taking ifstream as a parameter. I was more surprised to notice that this code works very well.

是编译器生成的构造函数还是有一些C ++引入的新特性11（带右值...）？

Are the constructor generated by the compiler or there is some new feature introduced by C++11 (with the rvalue...)?

推荐答案

在C ++中，最多允许一个用户定义的转换。您不能从 ifstream 直接构造 Algo_t ，但可以构造 Matrix_t 与 ifstream 。所以在

In C++ you are allowed up to one user defined conversion. You cannot directly construct a Algo_t from a ifstream but you can construct a Matrix_t with a ifstream. So in

Algo_t MyAlgo(ifstream(pMyFileName));

编译器构造一个临时 Matrix_t 一个用户定义的转换），然后使用该临时构造 MyAlgo

The compiler construct a temporary Matrix_t(your one user defined conversion) and then you use that temporary to construct MyAlgo

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