你在哪里使用一个朋友函数和一个静态成员函数？ [英] Where would you use a friend function vs. a static member function?

问题描述

当我们希望它访问该类的私有成员时，我们使非成员函数成为类的朋友。这给它与静态成员函数具有相同的访问权限。这两个选择都会给你一个函数，不与该类的任何实例相关联。

什么时候必须使用friend函数？我们什么时候必须使用静态函数？如果两者都是解决问题的可行选择，我们如何权衡它们的适用性？例如，当实现一个工厂创建类的实例 foo 它只有一个私有构造函数，如果工厂函数是 foo 的静态成员（你会调用 foo :: create（） create_foo（））？

解决方案

第11.5节C ++编程语言由Bjarne Stroustrup声明，普通成员函数获得3件事：

2. 必须在实例上调用


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朋友只能获得1个。





static 函数获取1和2。




We make a non-member function a friend of a class when we want it to access that class's private members. This gives it the same access rights as a static member function would have. Both alternatives would give you a function that is not associated with any instance of that class.

When must we use a friend function? When must we use a static function? If both are viable options to solve a problem, how do we weigh up their suitability? Is there one that should be preferred by default?

For example, when implementing a factory that creates instances of class foo which only has a private constructor, should that factory function be a static member of foo (you would call foo::create()) or should it be a friend function (you would call create_foo())?

解决方案

Section 11.5 "The C++ Programming Language" by Bjarne Stroustrup states that ordinary member functions get 3 things:

1. access to internals of class
2. are in the scope of the class
3. must be invoked on an instance

friends get only 1.

static functions get 1 and 2.

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