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From: oster@well.sf.ca.us (David Phillip Oster)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Need help with XCMD's and THINK C 4.0
Message-ID: <21165@well.sf.ca.us>
Date: 14 Oct 90 06:31:53 GMT
References: <15784@csli.Stanford.EDU>
Organization: Whole Earth 'Lectronic Link, Sausalito, CA
Lines: 68

In article <15784@csli.Stanford.EDU> dmr@csli.Stanford.EDU (Daniel M. Rosenberg) writes:
>We're trying to implement an XCMD in THINK C 4.0, and have followed
>the examples from the "How to build XCMD's in HyperCard book" as
>closely as possible.
Enclosed is the root of an XFCN I wrote. It implements an interface to
a proprietary file format, performaing many different functions, 
using the first argument as a function selector. Note the use of RememberA0(),
SetUpA4(). this is critical if you use any literal strings, since THINK C
references these off of its global pointer. (At least THINK C v.3 did.)
Sorry about the slightly non-standard nomenclature. When I sat down to write
this I discovered my Hypercard interface had succumbed to software root, so
I had to reconstruct it based on the HyperCard Script Langauge Guide.
This _IS_ verbatim quotes from working code that does file i/o, however.

#include <SetUpA4.h>
#include <HyperXCmd.h>

/* main - 
 */
pascal void main(xp)XCmdPtr xp;{
	RememberA0();
	SetUpA4();

	switch(ParamToNum(xp, 0)){
	case ABVERSION:		AFileVersion(xp);			break;
	case ABOPEN:		AFileOpen(xp);				break;
	case ABCOUNTRECS:	AFileCountRecs(xp);			break;
	case ABREADFIELD:	AFileReadField(xp);			break;
	case ABCLOSE:		AFileClose(xp);				break;
	case ABREADFIELDNAME:	AFileReadFieldName(xp);		break;
	case ABCOUNTFIELDNAMES:	AFileCountFieldnames(xp);	break;
	case ABSIGNATURE:	AFileSignature(xp);			break;
	case ABMASTERID:	AFileMasterID(xp);			break;
	case ABCURRENTSORT:	AFileCurrentSort(xp);		break;
	}

	RestoreA4();
}

#define private static
typedef long  LongInt;
typedef short Integer;

/* ParamToNum - given a parameter that should be numeric, return it.
 */
private LongInt ParamToNum(XCmdPtr xp, Integer n){
	Str255	s;
	LongInt	val;

	if(n >= xp->paramCount){
		return 0;
	}
	ZeroToPas(xp, *(xp->params[n]), s);
	val = StrToNum(xp, s);
	return (xresSucc == xp->result) ? val : 0;
}

/* ZeroToPas - write zeroes into memory
 */
pascal void ZeroToPas(XCmdPtr xp, char *zeroStr, StringPtr s){
	xp->inArgs[0] = (LongInt) zeroStr;
	xp->inArgs[1] = (LongInt) s;
	xp->request = xreqZeroToPas;
	(*xp->entryPoint)();
}
-- 
-- David Phillip Oster - Note new signature. Old one has gone Bye Bye.
-- oster@well.sf.ca.us = {backbone}!well!oster