From:	Nate Eldredge <neldredge AT hmc DOT edu>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Re: Forward reference....
Date:	08 Nov 1999 10:39:07 -0800
Organization:	InterWorld Communications
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"cywu" <cywu AT iii DOT org DOT tw> writes:

> Source code in xxx.h are as following:
> 
> /* Forward reference of OsTimer. This is so it can be used in the
> declaration
>  * of OsTimerNotify
>  */
>   93  typedef struct _OsTimer OsTimer;
>         typedef void (*OsTimerNotify)(OsTimer*);
>         typedef struct _OsTimer {
>           ListEntry        node;
>           TimeT            time;    /* Time period of the timer in TimeT
> units */
>           OsTimerNotify    func;    /* Pointer to function called when timer
> fires */
>           TimeT            startTime;
> 100     } OsTimer;
> but after compile, the error message is:
>     xxx.h:100: redefinition of 'OsTimer'
>     xxx.h:93: 'OsTimer' previously declare here

Hmm... here's one way to do it.

struct _OsTimer; /* This is the forward declaration */
typedef struct _OsTimer OsTimer; /* typedef it to the name we want */
typedef void (*OsTimerNotify)(OsTimer *);
/* Now actually define struct _OsTimer; it's the one thing not yet
	defined. */
struct _OsTimer {
	...
	OsTimerNotify func;
	...
};


-- 

Nate Eldredge
neldredge AT hmc DOT edu

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