Message-Id: <3.0.1.32.19970709094816.00593c68@mailhost.sm.ic.ac.uk>
Date: Wed, 09 Jul 1997 09:48:16 +0100
To: djgpp AT delorie DOT com
From: Paul Dixon <p DOT dixon AT ic DOT ac DOT uk>
Subject: Re: interesting redir behavior
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>`redir' relies on the fact that when you close handle x, the next open reuses that handle.  If this is false in OpenDOS, the redirected file will remain empty.
>
>It would be interesting to see whether this is indeed the problem.  Can 
>you compile `redir' (in src/utils/redir.c from djlsr201.zip) with -g, 
>step into it with a debugger and see what does `open' after `close' 
>return?

The redir code does indeed include several blocks of form

 if ( condition )
 {
  close(x); 
  if (open( argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0666 ) != x)
    fatal( "....cut...." );
  argc--; argv++;
 }

but the assumption made (that the old handle will be immediately reused) cannot be portable as it is based on no set standard. Wouldnt a revision of the code to use dup2(), as

 if ( condition )
 {
  int newhandle = open( argv[2], O_WRONLY | O_CREAT | O_TRUNC, 0666 );
  if ((newhandle < 0) || (dup2(newhandle, x) != x))
    fatal( "....cut...." );
  close(newhandle);
  argc--; argv++;
 }

be guaranteed to work portably regardless of underlying handle allocation strategy?
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Paul Dixon                                   Email: p DOT dixon AT ic DOT ac DOT uk
Software Engineer                          tel:   +44 (171) 725 1098
Academic Dept of Paediatrics               fax:   +44 (171) 725 6284
St Mary's Hospital Medical School
 (a constituent college of 
                  Imperial College of Science, Technology & Medicine)
Norfolk Place, London W2 1PG, UK
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