如何为每个循环传递成员函数? [英] How to pass a member function in for each loop?

问题描述

我正在尝试使用 std :: for_each()代替常规的 for 循环，但是我无法将成员函数传递给 for_each().

I'm trying to use std::for_each() instead of a normal for loop as a practice, but I can't pass a member function to for_each().

这是代码:

class Class
{
    public :
        void func (int a)
        {
            cout << a * 3 << " ";
        }
}ob1;

int main()
{
    int arr[5] = { 1, 5, 2, 4, 3 };
    cout << "Multiple of 3 of elements are : ";
    for_each(arr, arr + 5, ob1);
}

仅当此成员函数为 void operator()(int a)时，此方法才有效.我不知道为什么其他任何成员函数都不能传递到 for_each()！

It works only if this member function is void operator() (int a). I don't know why any other member function cannot be passed into for_each()!

推荐答案

您没有将任何类方法传递给 for_each()，而是传递了一个对象，该对象仅在该对象实现 operator().

You are not passing any class method to for_each(), you are passing an object, which only works when the object implements operator().

要让 for_each()调用您的 Class :: func()方法，您需要:

To let for_each() call your Class::func() method, you would need to either:

• 在您的课程中实现 operator():

class Class
{
public:
    void func (int a)
    {
        std::cout << a * 3 << " ";
    }

    void operator()(int a)
    {
        func(a);
    }
}ob1;

std::for_each(arr, arr + 5, ob1);

使用实现 operator()的单独委托来调用您的类.

use a separate delegate that implements operator() to call into your class.

• 您可以定义自定义函子(C ++ 11之前的版本):

• you can define a custom functor (pre-C++11):

struct functor
{
    Class &obj;

    functor(Class &c) : obj(c) {}

    void operator()(int a)
    {
        obj.func(a);
    }
};

std::for_each(arr, arr + 5, functor(ob1));

或使用 std :: bind() (C ++ 11和更高版本):

or use std::bind() (C++11 and later):

#include <functional>

auto func = std::bind(&Class::func, &obj1, std::placeholders::_1);
std::for_each(arr, arr + 5, func);

或使用 lambda (C ++ 11和稍后):

or use a lambda (C++11 and later):

auto func = [&](int a){ obj1.func(a); };
std::for_each(arr, arr + 5, func);

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