c - 从函数指针中读取数据是否合法？

Question

根据标准，从函数指针访问数据是否合法？

类似于:

#include <stdio.h>

int test(){
    //
}

int main() {
    int (*fp)(void) = &test;

    int i=0;
    for(i; i<10; ++i)
        printf("%x", *(fp+i));
}

Running on ideone ，它似乎有效 - 但我想知道它是否是预期的，或者它是否是实现定义的，并且该页面可能被操作系统读取保护？

Answer 1

从 C 标准的角度来看，不，不是。

N1570 中的 Annex J 有一章是关于常用扩展的:

J.5 Common extensions

1. The following extensions are widely used in many systems, but are not portable to all implementations. The inclusion of any extension that may cause a strictly conforming program to become invalid renders an implementation nonconforming. ...

然后在 J.5.7 函数指针转换中提到了这个扩展:

2. A pointer to a function may be cast to a pointer to an object or to void, allowing a function to be inspected or modified (for example, by a debugger) (6.5.4).