Thread: OOP with Incomplete types problem

Hi,

I'm new here but i've used this forum since i've started programing in C some month ago (btw, my nick is nosila, can a moderator / admin change that please? My bad), i have a school project to finish, it is mainly about creating a database program using list's, etc... I tryed to go over the top with this learning incomplete types and how i can use them to have some pseudo OO in C (i've experience with Java so i'm work really well with this) but i'm having all sorts of trouble doing it... So, what i have now is:

(this is not my actual project, just trying to resume it with the information i found more relevant)

Code:

Paint.h
#include Main.h
typedef struct _paint Paint;
Paint.c
#include Paint.h
struct _paint{

char * paint_color;
int paint_number;
};
Car.h
#include Main.h
typedef struct _car Car;
Car.c
#include Car.h
struct _car{
Paint * paint;
char * brand;
char * model;
};
Main.h
#include <stdio.h>
#include <stdlib.h>
#include "Paint.h"
#include "Car.h"

All of the header files have the #ifndef so the header is only defined once

Problem:
-How can i have a function in car that return the *paint???

if i have it like this

Paint * car_getPaint(Car * car);

it gives me errors in header file (in the beginning of this function signature) saying

error C2143: syntax error : missing '{' before '*'

------------


I've get this error in my project and in a "test" project i have created to test this kind of stuff... Anyone knows how to solve this??

PS: i've written this code here without testing so it may be possible i am missing some small things like ; or smtg!

You don't actually have anything called 'Paint' in your example. Consider:

Code:

/* foo.h */
typedef struct foo
{
    ...stuff...
} FOO;

/* some other file */
#include "foo.h"   /* now you can use FOO */

FOO *myfunthatreturnsfoo( void )
{
    ...
    return athingoffootype;
}

Quzah.

Why aren't you defining your structures in the header files? Anyway, car.h/.c doesn't have any reference or knowledge of paint.h, because it's not included for car.h/.c to see.


Quzah.

Originally Posted by Bayint Naung

Usual idiom:

foo.h // interface

Code:

#ifndef FOO_INCLUDED                // include guard
#define FOO_INCLUDED
enum { MAX_FOO_SIZE = 100 };

typedef struct foo foo;
foo *new_foo(int bar,char *s);
#endif

foo.c // implementation

Code:

#incude "foo.h"

struct foo {
   int bar;
   char *s;
};
foo *new_foo(int n,char *str) {
 ....
}

Yes, that always works but when i try to use 2 typedef's of incomplete type structs that i created, it gives-me error


Tried to typedef both structs in the header where i use them, and it works, like

typedef struct _car Car;
typedef struct _paint Pain;


but, do i really have to do that in EVERY header i use ? Shouldn't the #include combo take care of that??? This is BS, wasted a full day and a half thinking that doing that was plain stupid...

Originally Posted by anduril462

You're not really getting OO in C. An OO implementation on par with something like C++ or Java is pretty much impossible. You can implement a few of the features and design patterns (e.g. factory) this way. Nevertheless, hiding struct details can be useful. Bayint Naung gave the classic example I suggest you follow.

I would also avoid your crazy circular #include statements, with Main.h including Paint.h and Car.h, each of which include Main.h. Make things simple and logical. If the code in Car.c needs to know about stuff in Paint.h, include it. If not, don't. Same goes for Paint.h and Main.

Yes i know that, but at least is the most approximate OO i can get at least, in terms of encapsulation and data hiding...

Hum ok gonna change that I did that thinking that those typedef's would be "global", that way i could use any typedef anywhere..

Originally Posted by tabstop

It does, as you have it written in this thread (in that I have pasted into a set of files here and it compiles beautifully). If it's not working for you in your files, it's because you're not doing what you say you're doing.

Just for the record, what compiler are you using? Tomorrow i will upload my test project where i replicate that...

Thanks for all the help,

-NoSila