Question

参考:rel=“nofollow”> [33.11] Can 页: 1

#include "stdafx.h"
#include <iostream>

int f(char x, int y) { return x; }
int g(char x, int y) { return y; }

typedef int(*FunctPtr)(char,int);

int callit(FunctPtr p, char x, int y)  // original
{
    return p(x, y);
}

int callitB(FunctPtr p, char x, int y) // updated
{
    return (*p)(x, y);
}

int _tmain(int argc, _TCHAR* argv[])
{
    FunctPtr p = g;                    // original
    std::cout << p( c ,  a ) << std::endl;

    FunctPtr pB = &g;                  // updated
    std::cout << (*pB)( c ,  a ) << std::endl;

    return 0;
}

Question> Which way, the original or updated, is the recommended method? I have tested both methods with VS2010 and each prints the correct result.

谢谢。

Although I do see the following usage in the original post:

 void baz()
 {
   FredMemFn p = &Fred::f;  ← declare a member-function pointer
   ...
 }

Answer 1

Dereferencing a function pointer yields another function pointer. So, just f(), otherwise you re only obfuscating your code.

Pointers to members are different beasts altogether. They require usage of .* or ->* operators. That s also why you should use std::function (or boost::function) instead of raw pointers to functions/memebers.

Answer 2

Both are okay:

  p();
(*p)();

但是,第一种是可取的,因为它与校长更一致。例如,你可以撰写一个职能模板:

template<typename Functor>
void f(Functor fun)
{
     fun(); //uniform invocation - it doesn t matter what it is.
}

Now this can be called with function pointers, and functor object, both, which has been made possible only because I have used the first syntax.

故事的道德是:为穿制服,。书面守则,不论援引是否为职能单位或职能对象,都应当采用相同的方式。

Answer 3

The standard allows all of the forms you use, but unless you want to confuse readers, it s generally best to be explicit: &f to take the address of the function, and (*p)( x, y ) to call it.

Answer 4

You can use either form, but it looks most natural (to me) to use this:

p(x, y);

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