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From: burley@geech.ai.mit.edu (Craig Burley)
Newsgroups: comp.lang.fortran
Subject: Re: EQUIVALENCE or STRUCTURE/RECORD ?
Message-ID: <BURLEY.91Jan10095822@geech.ai.mit.edu>
Date: 10 Jan 91 14:58:22 GMT
References: <6683.278c85d2@cc.curtin.edu.au>
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In-reply-to: Gumley_LE@cc.curtin.edu.au's message of 10 Jan 91 07:18:42 GMT

In article <6683.278c85d2@cc.curtin.edu.au> Gumley_LE@cc.curtin.edu.au (Liam Gumley) writes:

   Main program

	   byte 		buffer(100)

   Subroutine (has 'buffer' passed to it)

	   byte 		buffer(100)
	   integer*4	data(20)
	   equivalence	( buffer(3), data(1) )

   The VAX compiler gives an error at the equivalence line.  Now I know I could
   do the equivalence in the main program and pass 'data' to the subprogram,
   but I would like to do it in the subroutine if I can.  Can I do this using
   structure and record statements, or some other way?

You can't equivalence dummies, as you have discovered.  Instead, use
STRUCTURE, UNION, and MAP to make the same thing.  I don't know if you'll
have to change the main program to pass the same data (STRUCTURE) type; I'd
guess not, since Fortran passes by reference anway and I don't think anything
about VMS' STRUCTURE facility requires passing additional information
(compare to CHARACTER type, which requires passing a length).

I don't have a VMS Fortran manual handy, but I'd guess what you need would
look something like this:

SUBROUTINE FOO(BUFFER)
STRUCTURE /BUFFERUNION/ BUFFER
   UNION
      MAP
         BYTE BYTES(100)
      END MAP
      MAP
         BYTE ignore(2)
         INTEGER*4 DATA(20)
      END MAP
   END UNION
END STRUCTURE

Then you'd refer to BUFFER.BYTES or BUFFER.DATA.  Good luck!
--

James Craig Burley, Software Craftsperson    burley@ai.mit.edu