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From: jwabik@umnd-cs.UUCP
Newsgroups: comp.lang.c
Subject: Help needed ->  fseek() and ftell() in VMS VAX C
Message-ID: <384@umnd-cs-gw.umnd-cs.UUCP>
Date: Wed, 11-Feb-87 17:00:45 EST
Article-I.D.: umnd-cs-.384
Posted: Wed Feb 11 17:00:45 1987
Date-Received: Fri, 13-Feb-87 02:28:28 EST
Organization: University of Minnesota at Duluth, Computer Science
Lines: 53
Keywords: It doesn't do what the manual says ..

I'm trying to fseek my way around a large (1.5MB) file using VAX VMS C,
and am having absolutely NO LUCK.  

Background:
	I developed software on UNIX to does what I need.  The UNIX code
	works just fine (and MUCH faster) on the UNIX box.  I moved the file
	to VMS, made the few cosmetic changes (like pathnames, etc..) 
	required to compile.  No problem.  Execution, on the other hand .. 

	After much grieving, I've come to the conclusion that fseek() and
	ftell() don't work the same (if at all!) on VMS as they do on UNIX,
	even though the VMS C manual says, "Functionally Equivalent".

Precise Problem Statement:

	1)  File is opened properly. 
	2)  I've converted LONG ftell variables from UNIX to INT 
	    ftell variables for VMS.  I've followed other instructions
	    in the manual as well.
	3)  fseek(fp,n,0) does NOT bring me to byte n in the file.  If
	    I do something like:

		for (i=0; i<512; i++) printf("%c",getc(fp));

	    after the fseek, in 95% of the cases I end up with nulls
	    or blanks printed -- almost as if I fseeked to before BOF 
	    or to after EOF.  In the other 5% of the cases I end up with 
	    data from the file, but data that is clearly not even 
	    reasonablly close to n in fp.  A ftell(fp) directly 
	    following this loop always returns a BIZARRE value like 
	    (n+x), where x is in the range of 100000..300000, or -n.  

     I've been playing with this problem for a few weeks -- I've 
     tried every other type of reading fp (fscanf, fgets, etc..),
     and numerous other things that I've long since forgotten.. 
     Just when I have a method that appears to work in a test
     program, it fails in the real code..  

     Help!!!  8^)  

     Is there a limit to N in fseek(fp,N,0)?  (Aside from the limits
     of the 32 bit integer.)  What would cause a large ftell() skip
     by reading 512 bytes?  (large > 100000)  HOW CAN I MAKE THIS 
     TO WORK?  Might this be a compiler bug?  Has anyone else experienced
     this VMS snafoo?  

     Thanks in advance!

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- Jeff Wabik, UMD Computing Services.   | ihnp4 \                            =
= University of Minnesota, Duluth  55812|         umn-cs!umnd-cs!jwabik      -
- "I feel fine."  -Spock.  Boo.  Hiss!  | ????? /			     =
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