Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!swrinde!kent
From: kent@swrinde.nde.swri.edu (Kent D. Polk)
Newsgroups: comp.lang.pascal
Subject: Re: How do you make a system call from PASCAL?
Keywords: UNIX SYSTEM CALL
Message-ID: <16274@swrinde.nde.swri.edu>
Date: 16 May 89 17:02:41 GMT
References: <2167@quanta.eng.ohio-state.edu>
Reply-To: kent@swrinde.UUCP (Kent D. Polk)
Distribution: usa
Organization: Southwest Research Institute, San Antonio, Texas
Lines: 61

In article <2167@quanta.eng.ohio-state.edu> segel@muon.eng.ohio-state.edu (Gargoyle) writes:
>
>	HELP!
>	Since I am not a normal PASCAL user, If you have a response, could
>you please e-mail it to me ASAP? Also This is being posted 5/12/89. Please
>do not respond after 5/16/89.
>
[...]
>	Is there such a call from PASCAL? Or
>do I have to write a C program to make the call, then have the PASCAL 
>program call that C subroutine? I know this can be done, but is there
>a simpler solution.
>
>-Mike Segel         segel@icarus.eng.ohio-state.edu   (614) 294-3350

While I haven't done this on a Sun, I have extensively on HP-UX/HP
Pascal, so I don't know whether it would apply.

Pascal variable parameter passing is just like C's passing an address.
Thus, for instance, to call ctime or nl_ctime, one would do something
like:

{*********************************}
Type datestr     = Packed array [0..25] of Char;
     datestr_ptr = ^datestr;

{ Forward External References }
Function ctime (Var nsec: Integer): datstr_ptr; External;
Function nl_ctime (Var nsec: Integer; Var format: string): datstr_ptr; External;
Function time (Var ds: Integer): External;

Var date : datestr_ptr;
    secs : integer;
Begin
   time (secs);
   
   New(date);
   If (format specified) then date := nl_ctime (secs, format)
   Else date := ctime (secs);

   {cleanup the string for pascal as desired}

   dispose(date);
End;

Now, exec'ing a program is done in a similar way, however, due to
Pascal limitations with file descriptors, I usually find that this is
done easier with a small C module which you declare as external & pass
the name of the file to exec'ed to it.

If in doubt about the size of a record or structure, most compilers
can be persuaded to divilge such info to make sure you have everything
described properly &
$include (header file describing the record structure in pascal)

Disclaimer : This is all from memory & I haven't done this in a couple
of years, but it ought to be close.

Lots of fun. Ought to try shared mem/message handling from Pascal next. :^)

Kent Polk