当它是一个类数据成员时，如何调用成员函数的指针？ [英] How to invoke pointer to member function when it's a class data member?

问题描述

struct B
{
  void (B::*pf)(int, int);  // data member
  B () : pf(&B::foo) {}
  void foo (int i, int j) { cout<<"foo(int, int)\n"; } // target method
};

int main ()
{
  B obj;
  // how to call foo() using obj.pf ?
}

在上面的测试代码中， pf 是 B 的数据成员。调用它的语法规则是什么？这应该是直接，但我没有得到一个适当的匹配。例如如果我尝试 obj。* pf（0,0）; 然后我得到：

In above test code, pf is a data member of B. What's the grammar rule to invoke it ? It should be straight forward, but I am not getting a proper match. e.g. If I try obj.*pf(0,0); then I get:

error: must use ‘.*’ or ‘->*’ to call pointer-to-member function in ‘pf (...)’, e.g. ‘(... ->* pf) (...)’

推荐答案

像这样：

(obj.*obj.pf)(0, 1);

会员访问（。优先于指向成员运算符的指针，因此这相当于：

Member access (.) has a higher precedence than a pointer to member operator so this is equivalent to:

(obj.*(obj.pf))(0, 1);

因为函数调用的优先级高于成员运算符的指针，所以你不能： / p>

Because function call also has higher precedence than a pointer to member operator, you can't do:

obj.*obj.pf(0, 1) /* or */ obj.*(obj.pf)(0, 1)

因为这相当于：

obj.*(obj.pf(0, 1)) // grammar expects obj.pf to be a callable returning a
                    // pointer to member

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