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From: shaula@maestro.mitre.org (Shaula Doyle)
Newsgroups: comp.lang.c
Subject: (hopefully)simple question
Keywords: bus error, book
Message-ID: <1991Apr5.132443.7726@linus.mitre.org>
Date: 5 Apr 91 13:24:43 GMT
References: <1991Apr04.183739.4876@group1.UUCP> <15714@smoke.brl.mil>
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Reply-To: shaula@maestro.mitre.org (Shaula Doyle)
Organization: The MITRE Corporation, McLean, Va
Lines: 34
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related declrations from top;
struct timeval wait;
struct timeval * wait_ptr;
timeout is parameter, earlier write statement showed to be 10.

1  if (TRACE)printf("read and except masks set\n");
2  if (timeout < 0) wait_ptr = 0;  /* set timeout characteristics */
3  else {
4	  wait.tv_sec = timeout;   /* 0 is immediate return */
5	  *wait_ptr = wait;
6	}
7  if(TRACE)printf("timeout set to %d\n",timeout);

A bus error came between the two trace statements on the _second_
iteration of the loop in which this was enclosed.
I changed line 5 from
	*wait_ptr = wait;
to
	wait_ptr = &wait;

and that fixed it.  My question is: why?  what was wrong?  I know
that a segmentation error means I tried to write outside my program
address space, can someone give me an explanation of what a bus 
error is?  I hope this isn't considered a waste of time, this seemed
to me the kind of esoteric C question this group would like.
FYI: I'm using cc under SunOS 4.1.1

-thanks for the time- shaula

PS I regularly program in about 3 different languages, and I find
I get confused on basic syntax sometimes.  K&R seems to make a 
horrible reference for this sort of simple detail, and I was 
hoping someone could recommend a good alternative?  thanx again.
shaula@maestro.mitre.org