Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!umd5!uvaarpa!virginia!scl
From: scl@virginia.acc.virginia.edu (Steve Losen)
Newsgroups: comp.sources.wanted
Subject: Re: Pascal to C conversion
Message-ID: <1019@virginia.acc.virginia.edu>
Date: 1 Aug 88 16:31:52 GMT
References: <336@sdrc.UUCP> <486@draken.nada.kth.se> <660@buengc.BU.EDU>
Reply-To: scl@virginia.acc.Virginia.EDU (Steve Losen)
Organization: University of Va., Charlottesville, VA
Lines: 56

On the subject of Pascal to C conversion utilities:  I know such beasts
exist, but I don't know any by name.  Offhand I can think of 3
areas to be very careful of when using such a program because Pascal
has several features for which C has no obvious counterpart.

1) Up level references.  In C, a function can only reference its own
   arguments, its own local variables, or global variables.  In Pascal,
   a function or procedure can also reference the local variables and
   arguments of other subprograms.  How does the translator handle the
   Pascal scope rules?  The most correct way would be to pass extra
   arguments to the C functions.  These  extra arguments would be pointers
   to the variables being referenced.

2) Set operations:  The translator will probably come with a library of
   set routines that the C programs call.

4) With statements:  These cannot be handled with simple textual
   substitutions.  For example,

	program test;
	type
		rec = record f1, f2 : integer;
	var
		a : array [1..10] of rec;
		i : integer;
	begin
		i := 5;
		with a[i] do begin
			for i := 1 to 10 do
				f1 := i;
		end
	end.

   According to the Pascal standard, a[i] is evaluated once
   at the beginning of the with statement.  All the references to
   "f1" within the with statement refer to the same memory location
   (even though "i" changes).  To get this right in C would require
   code like this:

	struct rec { int f1,f2;};

	main()
	{
		struct rec a[10], *p;
		int i;
	
		i := 5;
		p = &a[i-1];
		for(i=1; i<=10; i++)
			p->f1 = i;
	}

I'm sure there are other areas to watch out for.  Be sure your translator
does the job correctly or at least admits where it fails.
-- 
Steve Losen     scl@virginia.edu
University of Virginia Academic Computing Center