什么时候在C ++中使用函数对象？ [英] When do you use function objects in C++?

问题描述

我看到函数对象经常与STL算法一起使用。由于这些算法，功能对象是否出现？什么时候在C ++中使用函数对象？它的好处是什么？

I see function objects used often together with STL algorithms. Did function objects came about because of these algorithms? When do you use a function object in C++? What is its benefits?

推荐答案

如所说的jdv，使用函子而不是函数指针，编译器;此外，函子的一个基本优点是它们可以容易地保持对它们 ¹ 的调用之间的状态，因此它们可以根据其被调用的其他时间而不同地工作， ...

As said jdv, functors are used instead of function pointers, that are harder to optimize and inline for the compiler; moreover, a fundamental advantage of functors is that they can easily preserve a state between calls to them¹, so they can work differently depending on the other times they have been called, keep track somehow of the parameters they have used, ...

例如，如果要对int的两个容器中的所有元素求和，您可以这样做：

For example, if you want to sum all the elements in two containers of ints you may do something like this:

struct
{
    int sum;
    void operator()(int element) { sum+=element; }
} functor;
functor.sum=0;
functor = std::for_each(your_first_container.begin(), your_first_container.end(), functor);
functor = std::for_each(your_second_container.begin(), your_second_container.end(), functor);
std::cout<<"The sum of all the elements is: "<<functor.sum<<std::endl;

---

---

1. R Samuel Klatchko在下面指出，他们可以支持多个独立状态，每个functor实例一个：

1. Actually, as R Samuel Klatchko pointed out below, they can support multiple independent states, one for each functor instance:

一个稍微更精确的语句是函子可以支持多个独立状态（函数可以通过静态/全局变量支持单个状态线程安全或可重入）。

A slightly more precise statement is that functors can support multiple independent states (functions can support a single state via statics/globals which is neither thread-safe nor reentrant).

Functors允许您使用更复杂的状态，例如共享状态（静态字段）和私有状态（实例字段）。但是，这种进一步的灵活性很少使用。

这篇关于什么时候在C ++中使用函数对象？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！