C ++ 11 /生成的构造函数 [英] C++11 / Generated constructor

问题描述

我一直在从事其他人（离开公司）启动的C ++项目。他写了一段看起来不错的代码，但我听不懂。

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.

下面是该代码的简化版：

Here is below a simplified version of the code:

有两个类别：

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();
    }
};

主要：

有在主函数中进行以下调用：

There is the following call in the main function:

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

首先，我很惊讶该代码编译时没有任何错误，因为没有 Algo_t 以 ifstream 作为参数。
我更惊讶地注意到这段代码很好用。

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C ++引入了一些新功能11（带有右值...）？

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。您不能直接从 ifstream 构造 Algo_t ，但是可以构造 Matrix_t 和 ifstream 。因此，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 （您的一个用户定义的转化），然后您使用该临时变量来构造 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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