成员函数的函数指针

问题描述

我想将一个函数指针设置为类的成员，该类是指向同一类中另一个函数的指针。我这样做的原因很复杂。

I'd like to set up a function pointer as a member of a class that is a pointer to another function in the same class. The reasons why I'm doing this are complicated.

在这个例子中，我想输出为1

In this example, I would like the output to be "1"

class A {
public:
 int f();
 int (*x)();
}

int A::f() {
 return 1;
}


int main() {
 A a;
 a.x = a.f;
 printf("%d\n",a.x())
}

但是这在编译时失败。为什么？

But this fails at compiling. Why?

推荐答案

语法错误。成员指针是与普通指针不同的类型类别。成员指针必须与其类的对象一起使用：

The syntax is wrong. A member pointer is a different type category from a ordinary pointer. The member pointer will have to be used together with an object of its class:

class A {
public:
 int f();
 int (A::*x)(); // <- declare by saying what class it is a pointer to
};

int A::f() {
 return 1;
}


int main() {
 A a;
 a.x = &A::f; // use the :: syntax
 printf("%d\n",(a.*(a.x))()); // use together with an object of its class
}

ax 还没有说明该函数要调用的对象。它只是说你想使用存储在对象 a 中的指针。在。操作符的左操作数前面再次预处理 a 会告诉编译器调用函数上。

a.x does not yet say on what object the function is to be called on. It just says that you want to use the pointer stored in the object a. Prepending a another time as the left operand to the .* operator will tell the compiler on what object to call the function on.

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