函数参数vs函数参数的指针？ [英] Pointer to function parameter vs function parameter?

问题描述

我想了解以下两个声明之间的区别： f1 和 f2
在 f1 我声明这个参数是一个指向 void（）是 f2 声明不同于 f1 ？声明是等效的吗？在 main 中，我可以使用原型 void（）的函数调用它们。我理解通过值/指针/引用传递的概念，但是这些是函数，并不真正了解差异。它不像我可以修改作为参数传递的函数在 f1 ...谢谢！

I'd like to understand what is the difference between the 2 declarations, f1 and f2, below: In f1 I declare the parameter to be a pointer to a function of type void(), how is the f2 declaration different from the f1? Are the declarations equivalent? In main I can invoke both of them with functions of prototype void (). I understand the concept of passing by value/pointer/reference, however these are functions and don't really understand the difference. It is not like I can "modify" the function passed as parameter in f1... Thanks!

PS ：碰到众所周知的大多数Vexing解析问题时，由这个问题引发的）：

PS: came by this question when bumping into the well known Most Vexing Parsing problem :)

#include <iostream>

using namespace std;

void f1(void (*x)())
{
    x();
}

void f2(void x())
{
    x();
}

void g1()
{
    cout << "Invoking f1(g1())" << endl;
}

void g2()
{
    cout << "Invoking f2(g2())" << endl;
}


int main() 
{
    f1(g1);
    f2(g2);
}

程序编译，输出为

Invoking f1(g1())
Invoking f2(g2())

推荐答案

它们是等价的。

由于不能将函数作为参数传递给函数（你不能这样做）任何具有C中函数的函数，除非调用它们或获取它们的地址），编译器会静默地将参数更改为指向函数的指针。

Since you can't pass a function as an argument to a function (you can't do anything with functions in C other than call them or take their address), the compiler silently changes the argument into a pointer to a function.

与数组 - 你不能传递数组作为函数参数，所以任何时候你声明一个函数参数作为数组，它会静静地变成一个指针。

This is much the same as happens with arrays -- you can't pass arrays as function arguments either, so any time you declare a function argument as an array, it silently gets changed into a pointer.

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