Xref: utzoo comp.sys.mac.programmer:13132 comp.sys.mac:50513
Path: utzoo!attcan!uunet!clyde.concordia.ca!mcgill-vision!bloom-beacon!snorkelwacker!apple!amdahl!twg.com!lefty
From: lefty@twg.com (David N. Schlesinger)
Newsgroups: comp.sys.mac.programmer,comp.sys.mac
Subject: Re: Finding the current position of an open file--again
Message-ID: <205@gollum.twg.com>
Date: 12 Mar 90 21:22:49 GMT
Sender: news@twg.com
Organization: The Wollongong Group
Lines: 21
References:<5743.25f51321@george.uh.edu> <5753.25f634f1@george.uh.edu>

In article <5753.25f634f1@george.uh.edu> mike@george.uh.edu (Mike 
Frederick) writes:
> I have trapped a READ (xA002), and I can see the paramBlock with the
> ioRefNum in it.  Using only MacBugs, how can I get to the file mark?  I see
> something called a File Control Block which is kept in memory for each open
> file, and it a field called fcbCrPs which is described as "mark".  Is this
> what I want, and how do I get to the correct FCB from the paramBlock?

Yes, the fcbCrPs field _is_ what you want.  To find the appropriate FCB, 
take the ioRefNum from the parameter block and add it to the address stored at the low-memory global FCBsPtr (at location 0x34E).  This will get you a pointer to the appropriate FCB.

Hope this helps,

Lefty

|<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>|
|           David N. Schlesinger   ||   "When I have nothing to say,       |
|           The Wollongong Group   ||    my lips are sealed;               |
| Internet: Lefty@twg.com          ||    say something once,               |
| POTS:     415/962-7219           ||    why say it again?" -- David Byrne |
|<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>|