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Re: Pointers and Objects [message #35768 is a reply to message #35571]

Tue, 08 July 2003 06:47

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Johan Marais writes:

> I want to create an object with a pointer as one data member. When the
> object initialize it zero all the data members and the pointer becomes a
> NULL pointer. To me it seems that it is unusable now because you cannot
> change a NULL pointer. Anybody knows what can be done?

Well, you certainly can change a NULL pointer to *something*
or what would be the point? At the time you want to fill it
up, you could have code like this:

IF Ptr_Valid(self.ptr) THEN *self.ptr = mything ELSE $
self.ptr = Ptr_New(mything)

Or, if you want to initialize a pointer in the INIT method
to something that can always be dereferenced, you could
allocate memory, but not store anything. This is
essentially the same as storing an undefined variable in
the pointer:

self.ptr = Ptr_New(/Allocate_Heap)

Then, later:

*self.ptr = mything

Cheers,

David
--
David W. Fanning, Ph.D.
Fanning Software Consulting, Inc.
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155

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[Message index]

		Pointers and Objects By: Johan Marais on Tue, 08 July 2003 05:15
		Re: Pointers and Objects By: David Fanning on Tue, 08 July 2003 06:47
		Re: Pointers and Objects By: Michael Galloy on Thu, 15 March 2007 13:47
		Re: Pointers and Objects By: Robbie on Tue, 20 March 2007 19:13

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