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From: rwhite@nusdhub.UUCP (Robert C. White Jr.)
Newsgroups: comp.lang.c
Subject: Re: FILE * <-> System File Handles
Message-ID: <114@nusdhub.UUCP>
Date: Sat, 3-Oct-87 21:50:22 EDT
Article-I.D.: nusdhub.114
Posted: Sat Oct  3 21:50:22 1987
Date-Received: Thu, 8-Oct-87 01:29:17 EDT
References: <2.bagpiper@oxy.uucp>
Organization: National University, San Diego
Lines: 27
Summary: Simple Anwser to file problem.

In article <2.bagpiper@oxy.uucp>,  writes:
>  fprintf(stdprn,"This goes to the system printer!!") ;
>  otherptr = strprn ;
>  fprintf(otherptr,"And so does this...(on the same line even)\n") ;
>  fclose(otherptr) ;
>  fprintf(stdprn,"But this doesn't....???????\n") ;
> 

Your problem is very simple.

The type of stdprn is a pointer to FILE.  You coppied the pointer
value from stdprn into otherptr.  When you closed otherprinter you
were pointing to te same thing as stdprn.  Since both of the
pointers are identical [and therefore have the same MS-DOS file handle]
the single handle was closed.  Remember type FILE is a structure
one entry of which is the file handle is only one part.  This also
holds true for any UNIX STREAM.

Instead of the asignment you did in the code fragment, you should have
either used dup() or dup2() functions so that you had 2 seprate files
open to the same device.  NOTE: on MS-DOS versions before 3.0 the close
will still cause futrue writes to fail [do to an ms-dos bug] because 
the close routine will still sometimes close both file handles (this
from my Microsoft C manual.)  The code works correctly for 3.0 ms-dos
and above.

Robert ("So who asked you anyway?") White.