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From: nakada@husc4.HARVARD.EDU (paul nakada)
Newsgroups: comp.sys.apple
Subject: Re: Finding if a file exists on a disk in Applesoft BASIC.
Message-ID: <1701@husc6.UUCP>
Date: Mon, 20-Apr-87 21:21:49 EST
Article-I.D.: husc6.1701
Posted: Mon Apr 20 21:21:49 1987
Date-Received: Tue, 21-Apr-87 05:51:18 EST
References: <8704190657.AA12796@cdfb.toronto.edu> <1500@sphinx.uchicago.edu>
Sender: news@husc6.UUCP
Reply-To: nakada@husc4.UUCP (paul nakada)
Organization: Harvard Univ. Science Center
Lines: 23

>> Can anyone inform me how I can find out if a given file exists on the
>> disk or not through a BASIC (or a ML routine) program?
>> 
>> Right now, I am using VERIFY to see if the file name exists.  If it doesn't
>> exists (the desired case), it causes an error.  I use ONERR GOTO and use
>> an error handling routine to deal with it.  The problem is, it seems to
>> clear some GOSUB stacks, and when it encounters a RETURN, it comes back
>> with 'RETURN WITHOUT GOSUB ERROR', even though it was within a subroutine.

This problem is easily overcome using basic.  The key to it is
understanding the error handling in the apple.  The ONERR GOTO
statement is not a conditional gosub statement.  It does, although
save the current program location.  After the proper error correcting
statements are executed in the error routine (in this case, the
creation of a file) a RESUME command should be executed and not a
RETURN.  This will return to the point of the error where the error
has been corrected.  

Hope this helps...
paul nakada

nakada@husc4.harvard.edu
nakada@harvsc4.BITNET