you're right. it would have been more clever of me to actually look at my
own code first, or to think about it a moment longer. :-) i've pasted in
here my own code to replace FldHandleEvent in a Hack i wrote. this code
works for me.
Boolean __FldHandleEvent(FieldPtr pfld, EventPtr pEvent)
{
Boolean (*Trap)(FieldPtr, EventPtr) = 0; // original trap pointer
// get the address of original trap from HackMaster
FtrGet(idAppl, idcTRAP_FldHandleEvent, (DWord*)&Trap);
// detect when to activate
if (keyDownEvent == pEvent->eType)
{
DWord dwCfgPanel = 0;
FtrGet(idAppl, ftrCfgPanel, &dwCfgPanel);
if (dwCfgPanel)
goto Error;
// ... irrelevent code removed ...
}
Error:
// call original trap
return Trap(pfld, pEvent);
}
-----Original Message-----
From: Ade Barkah <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
Date: Tuesday, May 11, 1999 5:16 PM
Subject: Re: Basic Hackmaster Problem
>Hi Chris, Bob,
>
>I admit I'm rusty with my C, but in C++ at least, I'm afraid both you and
>Bob are mistaken.
>
>Declaring "Boolean oldTrap (FieldPtr, EventPtr)" does not make oldTrap
>a function pointer. Instead, it declares "oldTrap" as a function taking
>two arguments and returning Boolean. The (*) syntax must be used to make
>a function pointer. Having the '*' does not give you a pointer to a
>pointer to a function.
>
>If we had:
>
> Boolean oldTrap (FieldPtr, EventPtr);
> oldTrap = get_old_trap(); // Error! oldTrap not lvalue.
>
>If we instead had:
>
> Boolean (*oldTrap) (FieldPtr, EventPtr);
> oldTrap = get_old_trap() // Fine, oldTrap is a fn ptr.
>
>Now oldTrap is a function pointer, not a function. To use the oldTrap, it
>is optional to dereference it. That is:
>
> result = (*oldTrap) (fld, event); // Fine
> oldTrap (fld, event); // Also fine
>
>Perhaps this is why the confusion:
>
> Boolean realfunction (FieldPtr, EventPtr);
> Boolean (*oldTrap) (FieldPtr, EventPtr);
>
> oldTrap = realfunction; // Legal!
>
>It makes it seem as though 'realfunction' is a pointer to function. It
>is not. The following code is exactly equivalent to the last line above:
>
> oldTrap = &realfunction; // This is what is really
> // happening.
>
>That is, as a matter of convenience, once you have declared a function
>pointer, it is legal to omit the "&" when getting the address, and to
>omit the "*" when using the address.
>
>I'm sure the rules are the same with C, but you can test all of the
>above with your favorite C or C++ compiler. =-)
>
>Take care,
>
>-Ade
>
>
>At 03:47 PM 5/11/99 -0700, you wrote:
>>Bob is basically correct, but here's the root of the problem:
>>
>>a function pointer is (as should be obvious from the phrase) a pointer.
so
>>by declaring "Boolean oldTrap(FieldPtr, EventPtr);" you have already made
>>oldTrap be a pointer. so sticking that extra "*" in the declaration of
>>oldTrap is what's hosing you, because it turns "oldTrap" into a pointer to
a
>>pointer to a function, which is not what you want.
>>
>>
>>-----Original Message-----
>>From: Bob Ebert <[EMAIL PROTECTED]>
>>To: [EMAIL PROTECTED] <[EMAIL PROTECTED]>
>>Cc: Palm Developers Forum List <[EMAIL PROTECTED]>
>>Date: Tuesday, May 11, 1999 10:24 AM
>>Subject: Re: Basic Hackmaster Problem
>>
>>
>>>At 6:39 PM -0700 5/10/99, Mark Campillo wrote:
>>>>Boolean (*oldTrap)(FieldPtr, EventPtr);
>>>> //handled = oldTrap(fld, event); <-- This seems to be the problem line
>>>
>>>Well, honestly the pointer-to-function declaration syntax has always
>>>confused me, which is why I prefer typedefs, but I think it's the source
of
>>>your problem. The variable oldTrap in this case is a pointer to a
>>>function, so you need to dereference it in order to call it.
>>>
>>>That is, your line should be:
>>> handled = (*oldTrap)(fld, event)
>>>
>>>It would probably be clearer if you did something like this:
>>>
>>> // create the type
>>> typedef Boolean FldHandleEventFunction(FieldPtr, EventPtr);
>>>
>>> // declare the variable -- explicitly a pointer to a function
>>> FldHandleEventFunction *oldTrapP;
>>>
>>> // get the value
>>> FtrGet(myCreator, myResID, &oldTrapP);
>>>
>>> // call the function
>>> handled = (*oldTrapP)(fld, event)
>>>
>>>
>>> --Bob
>
>
>
