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From: toma@tekgvs.LABS.TEK.COM (Tom Almy)
Newsgroups: alt.msdos.programmer,comp.sys.ibm.pc.programmer
Subject: Re: Why won't DOS allow more than 20 open files?
Message-ID: <7642@tekgvs.LABS.TEK.COM>
Date: 11 Jun 90 16:38:31 GMT
References: <90160.191651JXS118@psuvm.psu.edu> <1990Jun10.151538.25462@xrtll.uucp>
Reply-To: toma@tekgvs.LABS.TEK.COM (Tom Almy)
Followup-To: alt.msdos.programmer
Organization: Tektronix, Inc., Beaverton,  OR.
Lines: 33

In article <1990Jun10.151538.25462@xrtll.uucp> silver@.UUCP (PUT YOUR NAME HERE) writes:
>In article <90160.191651JXS118@psuvm.psu.edu> JXS118@psuvm.psu.edu (Jeff Siegel, Op from Atherton Hall) writes:
>$Even though I have the statement FILES = 40 in my config.sys, DOS refuses
>$to open more than 20 files at once and returns error code 4 (no handles
>$available) if I try to open more. 

>   Yup.  Unless you fiddle DOS otherwise (and I forget how to), each process
>is only allowed 20 file handles, irrespective of your FILES= statement.  The
>FILES= statement controls how many files can be open at once, not how many
>one process can have open.

>   The workaround involves using some DOS call that expands the table of
>file handles for your process, but I've never done it and I can't recall
>how to do it.  I'm sure someone else will post it.

Well, the INT 21H call is:

AH =67H
BX = # desired handles

It returns carry flag clear if successful. The function is only available
in DOS versions >=3.3.

*BUT* if you are using a C compiler, and the stdio package, then you have
an additional hurdle. Every C compiler library I have seen maintains a static
table for FILE, which has 20 entries. The only way I know to expand these
tables is to have access to the library source, make the change, and recompile
the library. If you use open(), read(), etc. (not stdio), or many other
languages, then you are home free.

Tom Almy
toma@tekgvs.labs.tek.com
Standard Disclaimers Apply