声明 C++静态成员函数作为其所在类的友元（语法）

发布于 2024-12-23 16:34:06 字数 538 浏览 8 评论 0原文

将静态成员函数声明为其所在类的友元的语法是什么？

class MyClass
{
private:
  static void Callback(void* thisptr); //Declare static member
  friend static void Callback(void* thisptr); //Define as friend of itself
}

我可以将其折叠成一行吗？

class MyClass
{
private:
  friend static void Callback(void* thisptr); //Declare AND Define as friend
}

是否有另一种方法可以将其全部折叠成一行？

回答

请不要投反对票，这源于我对 C++ 静态成员函数缺乏了解。答案是他们不需要成为朋友，他们已经可以访问私人成员。所以我的问题有点无效。

原文

What is the syntax for declaring a static member function as a friend of the class in which it resides.

class MyClass
{
private:
  static void Callback(void* thisptr); //Declare static member
  friend static void Callback(void* thisptr); //Define as friend of itself
}

Can I fold it into this one-liner?

class MyClass
{
private:
  friend static void Callback(void* thisptr); //Declare AND Define as friend
}

Is there another way to fold it all into a single line?

Answer

Please don't downvote, this stems from my lack of knowledge about C++ static member functions. The answer is that they don't need to be friend, they already can access private members. So my question was somewhat invalid.

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萌梦深 2024-12-30 16:34:06

其实如果是静态的就不用用friend更准确了。静态成员函数可以像普通成员函数一样访问类的内部。唯一的区别是它没有 this 指针。

void MyClass::Callback(void* thisptr) {
    MyClass* p = static_cast<MyClass*>(thisptr);
    p->public_func(); // legal
    p->private_func(); // legal
    p->private_int_var = 0; // legal
}

Actually, no need to use friend if it is static is more accurate. A static member function has access to the internals of the class just like a normal member function. The only difference is it doesn't have a this pointer.

void MyClass::Callback(void* thisptr) {
    MyClass* p = static_cast<MyClass*>(thisptr);
    p->public_func(); // legal
    p->private_func(); // legal
    p->private_int_var = 0; // legal
}

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柳絮泡泡 2024-12-30 16:34:06

类成员函数不能是其自己类的友元 - 它已经是类成员并且可以访问其私有函数。和它交朋友有什么意义？这不是脸书...

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缱倦旧时光 2024-12-30 16:34:06

默认情况下，静态成员函数可以访问类的protected / private部分，无需将其设为friend。

#include <iostream>

struct Foo{
  Foo(int i) : an_int(i) {}

  static void print_an_int(Foo& self){
    std::cout << self.an_int;
  }
private:
  int an_int;
};

int main(){
  Foo f(5);
  Foo::print_an_int(f); // output: 5
}

A static member function has access to the protected / private parts of a class by default, no need to make it a friend.

#include <iostream>

struct Foo{
  Foo(int i) : an_int(i) {}

  static void print_an_int(Foo& self){
    std::cout << self.an_int;
  }
private:
  int an_int;
};

int main(){
  Foo f(5);
  Foo::print_an_int(f); // output: 5
}

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