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From: reagan@hiyall.enet.dec.com (John R. Reagan)
Newsgroups: comp.lang.pascal
Subject: Re: Read Files, How?
Message-ID: <12056@shlump.nac.dec.com>
Date: 30 May 90 17:12:14 GMT
Sender: newsdaemon@shlump.nac.dec.com
Organization: Digital Equipment Corporation
Lines: 50


In article <50800002@uxa.cso.uiuc.edu>, jlg0805@uxa.cso.uiuc.edu writes...
> 
>On standard Pascal, how can one interactively input a file name, then
>ask the program to read the file; ask the program to load another 
>file and repeat the same thing.
> 
>as my understanding, the external file name shoud appear in the program
>header.  However, this only works if actually there is a file with that
>very name.  If files have different names, then the machine gives an
>error. (mine is a sequent running unix), telling me "file not existent" 
>or something like that.
> 
>how to solve this problem? i hope it is not that one recompiles the 
>program for each new file.
> 
> 
>--The profs never teach useful practical things but stuff like AVL trees
>  in class. :-(
> 
>J.Liang
>jlg0805@uxa.cso.uiuc.edu
> 
> 
> 

Unextended Pascal (aka classic standard Pascal) had static binding
of files in the program header to external files in the file system.
It is upto an implementation to tell you how to set up this binding 
(like setting up aliases or environment variables, etc.)  However, it 
is still static for that invocation of the image.  You want dynamic binding 
(the ability to break a binding and recreate a new one in the same program 
based on some user input).

The sad news is that you can't do that in old unextended Pascal.  You'll
have to rely on vendor extensions (such as OPEN routines, etc.) or run
the program over again with a different static binding (I wouldn't think
you'd have to recompile).

In the Extended Pascal standard, there are now new routines called
BIND and UNBIND that perform much the same concept as some OPEN extensions.
Extended Pascal's binding allows you to do exactly what you want (of course
all file operations are implementation-defined in the sense that filenames
on one system might not be the same on other system...).

---
John Reagan
Digital Equipment Corporation
reagan@hiyall.dec.com
---