使用std :: thread调用重载的成员函数 [英] Calling overloaded member functions using std::thread

问题描述

是否有可能需要使用线程来重载函数？

Is it possible to have overloads for functions that we need to span using threads ?

我有一个简单的类，称为Complex。

I have a simple class called Complex.

class Complex
{
public:
    Complex():realPart_(0), imagPart_(0){}

    Complex(double rp, double ip) : realPart_(rp), imagPart_(ip) {}

    double & real() { return realPart_;}
    double & imag() { return imagPart_;}

    const double & real() const { return realPart_;}
    const double & imag() const { return imagPart_;}

    double square() const {return realPart_*realPart_ - imagPart_*imagPart_;}

    void display() const
    {
        std::cout << "Square of the Complex number (" << realPart_ << ") + i (" << imagPart_ << " ) is " << square() << std::endl;  
    }

    void display(unsigned nTimes) const {while(nTimes-- > 0)display();}

private:

    double realPart_;
    double imagPart_;

};

void Test3()
{
    Complex c1(1, 0.74), c2(2, 0.35);

    std::thread sqCalc1(&Complex::display, &c1);
    std::thread sqCalc2(&Complex::display, &c2);

    sqCalc1.join();
    sqCalc2.join();
}

构建此代码时会出错。

I get errors when I build this code.

error C2661: 'std::thread::thread' : no overloaded function takes 2 arguments

如果没有不带符号的重载显示函数，那么我显示的代码可以正常工作。

If there is no overloaded display function that takes an unsigned then the code I have shown works fine.

推荐答案

问题与 std :: thread 无关（错误具有误导性），可以通过重新排列代码来显示：

The problem is nothing to do with std::thread (the error is misleading), as can be shown by rearranging the code:

auto memfunc = &Complex::display;
std::thread sqCalc1(memfunc, &c1);
std::thread sqCalc2(memfunc, &c2);

错误现在将出现在第一行，因为正如其他答案所说，表达式& Complex :: display 指的是一个重载函数，编译器不知道您的意思是什么。

The error will be on the first line now, because as other answers have said, the expression &Complex::display refers to an overloaded function and the compiler doesn't know which one you mean.

您可以通过强制编译器告诉您要调用的函数的类型（使用强制转换或类似方法）来选择所需的重载：

You can select the desired overload by telling the compiler the type of the function you are trying to call, with a cast or like this:

void (Complex::*memfunc)() const = &Complex::display;
std::thread sqCalc1(memfunc, &c1);
std::thread sqCalc2(memfunc, &c2);

现在您已明确请求显示重载返回 void 并且不接受任何参数。

Now you've explicitly requested the display overload that returns void and takes no arguments.

如果编译器支持C ++ 11别名声明，则可以使更容易阅读：

If your compiler supports C++11 alias declarations you can make that easier to read:

using memfunc_type = void (Complex::*)() const;
memfunc_type memfunc = &Complex::display;
std::thread sqCalc1(memfunc, &c1);
std::thread sqCalc2(memfunc, &c2);

这篇关于使用std :: thread调用重载的成员函数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！