How to use address of function in function pointer?

Question

My following code is working fine. But I have little doubt, please see //Comment1 and //Comment2

#include<stdio.h>
#include<string.h>

struct PTR
{
    int (*funptr)(int);
};

int fun1(int)
{
    printf("Fun1\n");
    return 0;
}

int fun2(int)
{
    printf("Fun2\n");
    return 0;
}

int main()
{
    PTR p;
    p.funptr = &fun1; //Comment1
    p.funptr(5);

    printf("\n");

    p.funptr = fun2; //Comment2
    p.funptr(5);


  return 0;

}

Output : Fun1 Fun2

There is no problem in output.

At comment1 '&' opertor is used, so we are expllicing telling to get address, in comment2, we are not using '&', so which one is correct way?

How can you declare PTR p in main function without using struct name or typedef? — Raghu Srikanth Reddy, Jan 15 '14 at 06:56
But, Did this code compile? You neither typecasted nor used struct before PTR. — Raghu Srikanth Reddy, Jan 15 '14 at 07:19
@RaghuSrikanthReddy Code is compiled using Visual Studio. And there should not be any reason not to compile this code. You are creating Structure PTR ,and using it. Just to clarify, is it necessary in C++ to typedef a class, no. And class and struct are very same just with one little difference. — Pranit Kothari, Jan 15 '14 at 07:27
I compiled this code using gcc. and this question is tagged C, not C++. — Raghu Srikanth Reddy, Jan 15 '14 at 07:32
@RaghuSrikanthReddy Right now my virtual machine's Ubuntu not working, but whats the problem, why I need to typedef struct? — Pranit Kothari, Jan 15 '14 at 07:38
@RaghuSrikanthReddy I used extern "C" in my whole code, and working without problem. So both C/C++ way it is working. — Pranit Kothari, Jan 15 '14 at 07:41
let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/45285/discussion-between-raghu-srikanth-reddy-and-rockstartprogrammer) — Raghu Srikanth Reddy, Jan 15 '14 at 12:59

score 1 · Answer 1 · answered Jan 15 '14 at 06:03

1

Here,

p.funptr = &fun1 we are giving the address of the function. So '&' here is optional as p.funptr = fun1 also assign address of function.

answered Jan 15 '14 at 06:03

ajay_t

2,347
7
37
62

score 1 · Accepted Answer · answered Jan 15 '14 at 06:04

1

'&' is optional when taking the address of function。

answered Jan 15 '14 at 06:04

Zwy

353
1
10

How to use address of function in function pointer?

2 Answers2