Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!overload!dillon
From: dillon@overload.Berkeley.CA.US (Matthew Dillon)
Newsgroups: comp.sys.amiga.tech
Subject: Re:  Tags - How do they work.
Message-ID: <dillon.6960@overload.Berkeley.CA.US>
Date: 1 Nov 90 21:02:20 GMT
References: <53246.657345554@atronx.UUCP> <15486@cbmvax.commodore.com>
Lines: 85


    It turns out that it is extremely easy to implement stack-based tags,
    as someone on BIX pointed out to me.  Under 2.0, the Amiga.Lib already
    has routines to do this for some commands.... for example,

	OpenWindowTags()        -stack based tags method, tags are
				 individual arguments to the routine

	OpenWindowTagList()     -pointer to array of tags method, you
				 pass a pointer to the tags array.

    One can easily implement one's own routine to convert a stack based
    tags list into an array pointer tags list using VAR ARGS.  For
    example, the implementation of SystemTags() would be:

	#include <stdio.h>
	#include <stdarg.h>

	long
	SystemTags(cmd, ...)
	char *cmd;
	{
	    va_list va;
	    long error;

	    va_start(va, cmd);
	    error = System(cmd, va);
	    va_end(va);
	    return(error);
	}



The messages:

In article <15486@cbmvax.commodore.com> ken@cbmvax.commodore.com (Ken Farinsky - CATS) writes:
>I posted this the other day, which turned out to be wrong (as System()
>will not handle tags on the stack...)
>
>>>rc = System(argv[1],
>>>	       SYS_Input, infile,
>>>	       SYS_Output, outfile,
>>>	       SYS_Asynch, FALSE,
>>>	       TAG_DONE
>>>	       );
>
>Ewout sent me some mail, as follows:
>
>>>Ken, System() is tag, not stack based. So he'd have to do something like
>>>
>>>struct TagItem tag[5];
>>>
>>>tag[0].ti_Tag = SYS_Input;
>>>tag[0].ti_Data = infile;
>>>	.
>>>	.
>>>tag[4].ti_Tag = TAG_END;
>>>
>>>But the whole thing that guy is trying to do is wrong anyway since you cannot
>>>use a level 2 filehandle as an AmigaDOS BPTR filehandle.
>>>---
>>>Ewout Walraven - CATS			Commodore Business Machines, Inc.
>>>215-431-9426 			{uunet|rutgers}!cbmvax!ewout
>
>So, you have to put the tags into an array, then call System() with a
>pointer to the name of the command and a pointer to the tag array.
>Live and learn.
>
>>  Russell McOrmond   rwm@atronx.UUCP	 {fts1,alzabo}!atronx!rwm
>>  FidoNet 1:163/109  Net Support: (613) 230-2282
>>  Amiga-Fidonet Support  1:1/109
>--
>--
>Ken Farinsky - CATS - (215) 431-9421 - Commodore Business Machines
>uucp: ken@cbmvax.commodore.com   or  ...{uunet,rutgers}!cbmvax!ken
>bix:  kfarinsky

--

				    -Matt

    Matthew Dillon	    dillon@Overload.Berkeley.CA.US
    891 Regal Rd.	    uunet.uu.net!overload!dillon
    Berkeley, Ca. 94708
    USA