Thread: Naming pointer to function in a struct...

Okay, I'm writing a program where I need to use structs which contain two pointers to functions. I want to refer to these pointers as choose and decide... I'd like to know now if this code is the right way...

Code:

struct
{
 int ident;
 int (*choose) (int);
 int (*decide) (int);
} personality[NUM];

And is there any other way? Like maybe...

Code:

struct
{
 int ident;
 int (*) (int) choose;
 int (*) (int) decide;
} personality[NUM]

Also, I'd like to make sure that the following is a valid use of these function pointers.

Code:

j = (*personality[i].choose)(i);

I've never really used something like this before so... help me save a little time here anyone who already knows what the proper syntax is?

And oh yea, is there any way to name the parameters of the function.. you know, just for documentation? Like...

Code:

struct
{
 int ident;
 int (*choose) (int self);
 int (*decide) (int judgeMe);
} personality[NUM];

Yes, the first one is the right way. However, you can make it cleaner and easier to understand with a typedef:

( hope it's correct, I don't have a compiler here... )

PHP Code:


#include <stdio.h>

typedef int (*FUNCTION_POINTER_INT2INT)(int);

const unsigned int NUM = 2;

struct
{
    int ident;
    FUNCTION_POINTER_INT2INT choose;
    FUNCTION_POINTER_INT2INT decide;
} personality[NUM];

int test( int i )
{
    return i*2;
}

int main()
{
    personality[0].choose = test;

    printf( "%d", personality[0].choose( 5 ) );

    return 0;
} 


Ehhe, okay, now I have another problem...

Code:

enum {kind, usurper, egoist, NUM};

struct
{
 int ident;
 int (*choose) (void);
 int (*decide) (int);
} personality[NUM];

int kind_choose (void);
int kind_decide (int judgeMe);

personality[kind] = {kind, kind_choose, kind_decide};

Let me be the first to say that this did not work.

I'm sure there's other problems with this, but the first problem is that
personality[kind] = {kind, kind_choose, kind_decide};
looks like a declaration of an array of kind elements, not the assignment of values struct personality[kind] (admittedly, this probably isn't even a legal way to assign values to a struct).

This leaves me in kind of a problem, because I would like a nice and easy way to add and remove personalities. I considered using something like this...

Code:

#define ASSIGNPERSONALITY(A) \\
{ personality[A].ident = A; \\
  personality[A].choose = A ## _choose; \\
  personality[A].decide = A ## _decide; }

But at first I'm not even sure this will work, since each A is going to be an enum constant, and I think that this is a pretty confusing construct anyhow.

So anyways, does anyone have a suggestion for a good way for me to -easily- add/remove personalities when I compile?

The only thing wrong with your last example is failure to include 'struct' before it, that and you haven't named your structure. I'd do something like:

Code:

struct personalityTypes {
    int ident;
    int (*chose)(void);
    int (*decide)(int);
};

Then build a table, I think you could use your macro, but let me clarify, you want a compile-time list change, not a runtime? A compile time change could use something like:

Non-macro version:

Code:

struct personalityTypes personalityTable[] =
{
    { kind, kind_choose, kind_decide },
    { usurper, usurper_choose, usurper_decide },
    ... more ... 
};

Or, with slight modification, your macro might work, I personally haven't tried, but I believe it should do the trick:

Macro version:

Code:

#define PERSONALITY(A) { A, A ## _chose, A ## _decide }

struct personalityTypes personalityTable[] =
{
    PERSONALITY(kind),
    PERSONALITY(usurper),
    PERSONALITY(egoist)
}

That should do the trick.

Quzah.