How can I modify a function by C pointer？Can it be done？

Question

First, define two functions. Then, assign the address represented by the function name to two ordinary pointers. Finally, copy the value pointed to by one pointer to the memory pointed to by another pointer. Output the same result by calling different functions? How can i achieve it? Or can it be achieved?

Have you tried to do the steps that are described here? At which step are you stuck? What is the problem? — mkrieger1, May 09 '21 at 13:48
Please check these answer. It already given on stackoverflow [ModifyPointer](https://stackoverflow.com/questions/35609109/modify-pointer-value-in-a-function/35609326) [ModifyPointer](https://stackoverflow.com/questions/766893/how-do-i-modify-a-pointer-that-has-been-passed-into-a-function-in-c) — Muhammad, May 09 '21 at 13:50
Why is the sentence "Output the same result by calling different functions" written like a question? — mkrieger1, May 09 '21 at 13:51
Actually this is not a problem, it’s just that I’m curious. It seems that someone has already explained. — Fantety, May 09 '21 at 23:31

score 0 · Answer 1 · answered May 09 '21 at 13:52

0

#include <stdio.h>
#include <stdlib.h>

void f(int *x)
{
    int j=7;
    *x=j;
    printf("%d-",*x);

} 

int main()
{
    int i=66 ;
    int *x;
    x=&i;
    f(x);
    printf("%d",*x);

    return 0;

}

answered May 09 '21 at 13:52

Muhammad

19
2

1

Where does this “assign the address represented by the function name[s] to two ordinary pointers” as requested by the question? – Eric Postpischil May 09 '21 at 14:10
Well, I shared it what I understand from your question. Please let know when you are asking exactly. Or add your code into question. So I can fix it – Muhammad May 09 '21 at 14:11
I am not the OP. – Eric Postpischil May 09 '21 at 14:12

score 0 · Accepted Answer · answered May 09 '21 at 14:12

C does not support modifying functions at run-time. Copying the bytes of one function to another function is not likely to work. In common C implementations, the memory of functions is marked read-only, and modifying it requires special steps to change that. Even if you can write to the memory, instructions may be different depending on where they are located in memory—they may use absolute addresses or offsets from special reference points—so the copied instructions will not work in their new locations.

How can I modify a function by C pointer？Can it be done？

2 Answers2