指向成员函数的指针 [英] Pointer to a member-function

问题描述

我想做以下事情：
我有两个类，A和B，并且想绑定一个函数从A到B的函数，所以每当有人调用B的函数，函数从A被调用。

I would like to do the following: I have two classes, A and B, and want to bind a function from A to a function from B so that whenever something calls the function in B, the function from A is called.

基本上，这是场景：
（ important A和B应该是独立的类）

So basically, this is the scenario: (important A and B should be independent classes)

这将是A类：

class A {
private:
    // some needed variables for "doStuff"
public:
    void doStuff(int param1, float *param2);
}

这是B类

class B {
private:
    void callTheFunction();

public:
    void setTheFunction();   

}

这是我想要使用这些类：

And this is how I would like to work with these classes:

B *b = new B();
A *a = new A();

b->setTheFunction(a->doStuff); // obviously not working :(

我读过，这可以通过std :: function ，这将如何工作？此外，这是否会影响性能每当 callTheFunction（）被调用？在我的示例中，它的一个音频回调函数，应该调用

I've read that this could be achieved with std::function, how would this work? Also, does this have an impact in the performance whenever callTheFunction() is called? In my example, its a audio-callback function which should call the sample-generating function of another class.

推荐答案

基于用法的解决方案C ++ 11 std :: function和std :: bind 。

Solution based on usage C++11 std::function and std::bind.

#include <functional>
#include <stdlib.h>
#include <iostream>

using functionType = std::function <void (int, float *)>;

class A
{
public:
    void doStuff (int param1, float * param2)
    {
        std::cout << param1 << " " << (param2 ? * param2 : 0.0f) << std::endl;
    };
};

class B
{
public:
    void callTheFunction ()
    {
        function (i, f);
    };

    void setTheFunction (const functionType specificFunction)
    {
        function = specificFunction;
    };

    functionType function {};
    int     i {0};
    float * f {nullptr};
};

int main (int argc, char * argv [])
{
    using std::placeholders::_1;
    using std::placeholders::_2;

    A a;
    B b;
    b.setTheFunction (std::bind (& A::doStuff, & a, _1, _2) );
    b.callTheFunction ();

    b.i = 42;
    b.f = new float {7.0f};
    b.callTheFunction ();

    delete b.f;
    return EXIT_SUCCESS;
}

编译：

$ g ++ func.cpp -std = c ++ 11 -o func

$ g++ func.cpp -std=c++11 -o func

输出： p>

Output:

$ ./func

$ ./func

0 0

42 7

这篇关于指向成员函数的指针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！