Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!hellgate.utah.edu!helios.ee.lbl.gov!ux1.lbl.gov!beard
From: beard@ux1.lbl.gov (Patrick C Beard)
Newsgroups: comp.sys.mac.programmer
Subject: Re: SndNewChannel crashes my program!
Keywords: c, Sound, snd, code
Message-ID: <4846@helios.ee.lbl.gov>
X-Local-Date: 14 Feb 90 02:03:40 PST
Date: 14 Feb 90 10:03:40 GMT
References: <7605@tank.uchicago.edu>
Sender: usenet@helios.ee.lbl.gov
Reply-To: beard@ux1.lbl.gov (Patrick C Beard)
Distribution: usa
Organization: Lawrence Berkeley Laboratory, Berkeley
Lines: 47

In article <7605@tank.uchicago.edu> fri0@tank.uchicago.edu (Christian E. Fritze) writes:
#
#Dear Netters!
#
#I'm a beginning Mac programmer trying to use the sound manager routines to play
#some sampled sound.  Why does the following code (an excerpt from my THINK C
#4.0 program) break my Mac at the indicated function call?  Odd address, says
#the debugger; sound doesn't play.  IMV says that passing a NIL pointer to
#SndNewChannel tells SndNewChannel to allocate a channel for you and return it. 

##include <SoundMgr.h>
##define NULL	0L
#
#main()
#
#{
#
#SndChannelPtr	soundPtr;
#Handle			soundHndl;
#OsErr			Check;
#	
#soundHndl = GetResource('snd ',16658);
#
#	/*This call does it... */
#Check=SndNewChannel(&soundPtr,sampledSynth,initSRate22k,NULL);

As you said, IMV says that passing a NIL pointer gets you a new channel.
You forgot to initialize the variable soundPtr to nil!  Therefore, you
get a crash when SndNewChannel gets whatever happens to be on the stack.

I won't comment on the "stupidity" of this question.  Apple, why did
you come up with such a bizarre way to allocate a channel?  I much
prefer the NewWindow method.  In other words, we can preallocate memory
for Windows and pass it to NewWindow:

	WindowPtr myWindow = (WindowPtr)NewPtr(sizeof(WindowRecord));
	
	WindowPtr w = NewWindow(myWindow, bounds, title, visible, procID, 
							behind, goAwayFlag, refCon);

I suppose the rationale was that an OSErr code should be returned
because opening a channel does more than allocate memory for the
channel record, but perhaps a SoundError() function would be better.
-------------------------------------------------------------------------------
-  Patrick Beard, Macintosh Programmer                        (beard@lbl.gov) -
-  Berkeley Systems, Inc.  ".......<dead air>.......Good day!" - Paul Harvey  -
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