函数指针作为结构的静态成员

Question

Please look at the definition of the structure below:

struct rectangle
{
   int len,bre;
   static int diagonal;
   static (int) (*ptr) (int,int);
};

int rectangle::diagonal;
rectangle::ptr; // (WHAT SHOULD COME HERE)

rectangle r1,r2;

Hi friends, I have defined a structure here. We know that the size of 'r1' or 'r2' is sum of the members 'len and 'bre' only.

Now to allocate memory for the static members we must do it explicitly. The allocation for the static member diagonal is fine. But what should I give in the place: (WHAT SHOULD COME HERE) so that the memory allocation for the function pointer is fine.

Hope my explanation is clear to you. Please do help me.

Answer 1

The easiest way is to typedef a function and use it there:

typedef int (*MyFunction) (int,int);
struct rectangle
{
    ...
    static MyFunction ptr;
};
MyFunction rectangle::ptr = /*initialize it here*/

But also you can do it as int (*rectangle::ptr)(int,int)

Answer 2

Below is the correct way:

struct rectangle
{
...
   static int (*ptr) (int,int);
       // ^^^ no braces needed
};

int (rectangle::*ptr) (int, int);
//   ^^^^^^^^^^^^^^ defining a function pointer

Whenever there is a confusion related to function pointer, make a typedef and use it:

typedef int (*fptr) (int,int);
struct rectangle
{
   static fptr ptr;
};

fptr rectangle::ptr;

Answer 3

Try:

struct rectangle
{
   int len,bre;
   static int diagonal;
   static int (*ptr) (int,int);
};

int rectangle::diagonal;
int (*rectangle::ptr)(int,int) = NULL;

rectangle r1,r2