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Re: objects and call external [message #29368 is a reply to message #29273]

Tue, 12 February 2002 20:12

Mark Rivers
Messages: 49
Registered: February 2000

Member

Gert <gert.van.de.wouwer@NO_SPAMpandora.be> wrote in message
news:SJea8.136468$rt4.12914@afrodite.telenet-ops.be...
> hi,
>
> I try to use a call_external in an object method like this:

> pro MCP2000__DEFINE
> struct = {MCP2000, hComm: 0l, status: 0l}
> end

> function MCP2000::Init
> self.hComm = 0l
> return, 1
> end

> function MCP2000::InitPort
>
self.status=call_external('D:\Cpp\SerCommDll\Debug\SerCommDl l.dll','InitPort
Dll',$
> /PORTABLE,'COM1',self.hComm ,/UNLOAD)
> return, self.status
> end
>
> the idea is here that self.hComm contains a valid handle, but it doesnt -
it stays zero.

Your problem has nothing to do with CALL_EXTERNAL or the fact that you are
using an object method. The problem is that when you pass self.hComm (to
any routine) IDL views that as an "expression" and passes a copy of
self.hComm, not the address of self.hComm. Thus you cannot modify
self.hComm in the called routine. It is analogous to C passing integers by
value - the called routine can write into the function parameter, but the
calling routine does not see the resulting change. Your second way of doing
it is correct, pass "temp" and copy "temp" to self.hComm on the return.

Mark Rivers

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[Message index]

		objects and call external By: Gert on Tue, 12 February 2002 12:15
		Re: objects and call external By: Gert Van de Wouwer on Wed, 13 February 2002 06:18
		Re: objects and call external By: Gert Van de Wouwer on Wed, 13 February 2002 05:18
		Re: objects and call external By: Mark Rivers on Tue, 12 February 2002 20:12

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