TweetFollow Us on Twitter

XCMD in App
Volume Number:9
Issue Number:7
Column Tag:C Workshop

XCMD’s in Standalone Applications

Here’s a way to write XCMD’s so they’re usable for more than HyperCard

By Gerry H. Kenner, Magna, Utah

Note: Source code files accompanying article are located on MacTech CD-ROM or source code disks.

About the author

Gerry Kenner is a professional electrical and computer engineering consultant, university researcher and sometimes writer who specializes in image analysis systems for investigative scientists.

INTRODUCTION

This paper shows how to access HyperCard XCMDs which have been incorporated into the resource file of a standalone application. This is done by creating a function named LoadXCMD which takes the name and parameters of an XCMD and provides glue code for accessing them. In addition, code is provided for responding to callbacks by the HyperCard utility functions.

HyperCard stacks are unequaled as dynamic front ends for interfacing with scientific instruments. Hypercard facilitates entering data and displaying results by using buttons and text fields. Elaborate front ends can be thrown together in a matter of hours and the resulting scripts can be altered within minutes when rapid changes in the interface are required.

One major problem with HyperCard stacks is the slow execution speed of the HyperTalk scripts. Fortunately, they can be speeded up by liberal use of XCMD’s and XFCN’s for time intensive operations.

A price is paid for these advantages. Most obvious is that HyperCard stacks can become very large. Another disadvantage is that they are susceptible to damage. One quickly learns to keep at least two back-up copies of working stacks. A more subtle problem is that of bullet-proofing large Hypercard programs so that the average technical person can run them.

Once the stacks become finalized, one alternative is to replace them with standalone applications developed using THINK C with objects. The THINK Class Libraries can be used to provide the replacement interface. The XCMD’a and XFCN’s could be modified into modules which could be called by the application or else incorporated directly using the system described in this paper. An application prototyper such as AppMaker or Marksman would be invaluable for this.

I obtained some insights on how to incorporate XCMD’s into standalone applications from a note in the October 1989 MacTutor by Peter B. Nagel of Denver, CO. With this information as a basis I proceeded to write the demo code published here.

Disclaimer

As in my previous articles I am only including the code necessary to understand the project. This code is enough for an intermediate programmer to fill in what is missing. Typically, I do not declare variables or state which header files must be included. A copy of the complete project is available on the MacTutor Disk.

STANDALONE APPLICATION

The standalone program passes the number 5 and the message “Return to application” to a modified version of Apple’s Flash XCMD demo which inverts the screen 5 times (flashes) and returns a message which is then displayed in a window.

The program requires two files, pTest and pXCMD. PTest is an entry file containing the main function which needs code for initializing the toolbox, creating a window, calling the XCMD and outputting the return value to the window. The XCMD function call is as follows.

/* 1 */

TempHdl = LoadXCMD(3, “pXFCN”, “5”, “Hello World!”);

Three is the number of parameters being passed, pXFCN is the name of the XCMD code resource, 5 is the number of beeps requested while “Hello World” is the string which will be returned by the XCMD. TempHdl points to the return string.

Although the memory allocated to TempHdl was assigned elsewhere, it must be deallocated with a call to DisposHandle.

The pXFCN.h file references HyperXcmd.h and declares prototypes of four functions. The function declarations are as follows.

/* 2 */

Handle LoadXCMD(short Count, ...);
void JumpToXCMD(XCmdPtr ParamPtr, Handle CodeAddr);
void SwitchXCMD(void);
char *StrCpy(char *s1, char *s2);

It also contains an enum list of Apple’s HyperCard request codes. Complete lists of these can be found in the pre 1988 HyperCard header files. To facilitate identification, I am including a partial list here.

enum {  
 xreqSendCardMessage = 1,
 xreqEvalExpr,
 xreqSendHCMessage = 5;
 xreqSendHCMessage = 8;
 
 ...

 xreqScanToReturn,
 xreqScanToZero = 39   // was suppose to be 29!  Oops!
};

The function LoadXCMD takes the parameters passed, converts them into XCMD readable form and then calls the code resource. The code is as follows.

/* 3 */

1. Handle LoadXCMD(short Count, ...)
2. {
3. void *ListPtr;
4. char *CharPtr;
5. Handle CodeAddr, TempHdl;
6. shorti, Err;
7. size_t Size;
 
8. Count = Count - 1;
9. ListPtr = &Count + 1;
10.CharPtr = *(*(char***)&ListPtr)++;
11.CtoPstr(CharPtr);
12.CodeAddr = GetNamedResource(‘XFCN’, CharPtr);
13.MoveHHi(CodeAddr);
14.HLock(CodeAddr);

15.ParamPtr = (XCmdPtr)NewPtr(128L);
16.ParamPtr->entryPoint = (Ptr)SwitchXCMD;

17.ParamPtr->paramCount = Count;
18.for (i = 0; i < ParamPtr->paramCount; ++i)
19.{
20.ParamPtr->params[i] = NewHandle(256);
21.HLock(ParamPtr->params[i]);
22.CharPtr = *(*(char***)&ListPtr)++;
23.strcpy((char*)*(ParamPtr->params[i]), CharPtr);
24.}
 
25.JumpToXCMD(ParamPtr, CodeAddr);
26.Size = strlen(*(ParamPtr->returnValue));
27.TempHdl = NewHandle((long)Size);
28.strcpy((char*)*TempHdl, 
 (char*)*(ParamPtr->returnValue));
29.HLock(TempHdl);
 
30.for (i = 0; i < ParamPtr->paramCount; ++i)
31.{
32.HUnlock(ParamPtr->params[i]);
33.DisposHandle(ParamPtr->params[i]);
34.}
35.HUnlock(CodeAddr);
36.HUnlock(ParamPtr->returnValue);
 
37.DisposHandle(ParamPtr->returnValue);
38.DisposPtr((XCmdPtr)ParamPtr);
39.ReleaseResource(CodeAddr);
 
40.return(TempHdl);
41.}

Instruction 8 retrieves the number of parameters passed. Instructions 9 through 12 get the name of the XCMD and load the resource code. The address of the XCMD is obtained by using GetResource to load the code resource into memory and get a handle to its location. Instruction 15 allocates memory for the XcmdBlock pointed to by ParamPtr. ParamPtr was declared as a global since it is used both here and by SwitchXCMD. Instruction 16 sets up the function SwitchXCMD as the entry point for HyperCard XCMD utility calls. Instructions 17 through 24 finish setting up the XcmdBlock for the XCMD call. Note that space was not allocated for returnValue even though the code disposes of a handle to this value before terminating. Variables were assigned to params[0] and params[1].

Instruction 25 calls the function JumpToXCMD which is an assembly lanquage glue routine for placing the address of the XCmdBlock on the stack and then jumping to the address of the XCMD (actually XFCN in this case). Instructions 26 through 29 prepare the contents of returnValue for passing back to the calling function. The final portion of the function disposes of the various handles and pointers created in the program. CodeAddr was disposed of with ReleaseResource.

After returning from JumpToXCMD, the function StrCpy was used to copy returnValue into a temporary string. StrCpy was used rather than the ANSI library routine strcpy to avoid the possibility of LoadSeg being called with attendent movement of memory. This is necessary because the compiler will not permit the locking of the handle returnValue, apparently because the handle was not created within the function.

Here is the code for JumpToXCMD.

/* 4 */

1. void JumpToXCMD(XCmdPtr ParamPtr, Handle CodeAddr)
2. {
3. asm
4. {
5. move.l ParamPtr(a6), -(a7)
6. move.l CodeAddr(a6), a0
7. move.l (a0), a0
8. jsr  (a0)
9. }
10.}

The address of the XCmdBlock is moved on to the stack in line 5 while the handle pointing to the code resource is moved into register A0, dereferenced twice and then jumped to in lines 6 to 8.

Remember that the address of the function SwitchXCmd was placed in the entryPoint field of the XCmdBlock. This is the code which is jumped to when HyperCard utility functions are called. It consists of a switch statement which identifies the code for each utility function. I am only going to show the code for PasToZero and SendHCMessage but the principal applies to accessing all the functions. The code itself is self-explanatory and doesn’t require a detailed explanation.

/* 5 */

void SwitchXCMD(void)
{
 WindowPtrTempWindow, OldPort;
 Handle TempHandle;
 long   TempLong;
 Str255 TempStr;
 Rect   TempRect;
 
 switch (ParamPtr->request)
 {
 case xreqZeroToPas:
 strcpy((char*)ParamPtr->inArgs[1], 
 (char*)ParamPtr->inArgs[0]);
 CtoPstr((char*)ParamPtr->inArgs[1]);
 break;
 
 case xreqSendHCMessage:
 GetPort(&OldPort);
 SetRect(&TempRect, 20, screenBits.bounds.bottom - 80, 
 480, screenBits.bounds.bottom - 20);
 TempWindow = NewWindow(0L, &TempRect, “\pHC Message”, 
 TRUE, plainDBox, (WindowPtr)-1L, TRUE, 0L);
 SetPort(TempWindow);
 MoveTo(10, 30);
 DrawString((char*)ParamPtr->inArgs[0]);
 Delay(90L, &TempLong);
 DisposeWindow(TempWindow);
 SetPort(OldPort);
 break;
 
 default:
 break;
 }
}

Writing to code for StrCpy is left as an exercise for the reader. My version is written in assembly lanquage.

THE XCMD (XFCN)

For completeness I have included a partial listing of CFlash, the modified XCMD which is called by pXFCN. This example uses the HyperCard utilites SendHCMessage and ZeroToPas. In addition it uses several Toolbox function calls and the C library call strcpy.

There is a problem with some of the C library calls. Functions which do not use globals referenced from A5 or A4 appear to work without problems. Thus, strcpy and strcat can be used. Routines such as atoi and atol which use globals will not run properly in the program as written and attempts to use them often result in crashs.

/* 6 */

 RememberA4();
 SetUpA4();
 
 HLock(paramPtr);
 paramPtr->returnValue = NewHandle(256L);
 StrPtr = (StringPtr)NewPtr(256L);
 
 ZeroToPas(paramPtr, (char*)*(paramPtr->params[0]), StrPtr);
 StringToNum(StrPtr, &TempLong);
 flashCount = (int)TempLong;
 
 GetPort(&port);
 for (again = 1; again <= flashCount; again++) 
 {
 InvertRect(&port->portRect);
 InvertRect(&port->portRect);
 }
 
 SendHCMessage(paramPtr, 
 (StringPtr) ”\pput \”This is a message\” into msg”);
 Delay(60L, &TempLong);
 
 strcpy((char*)*(paramPtr->returnValue), 
 (char*)*(paramPtr->params[1]));
 DisposPtr(StrPtr);
 RestoreA4();
 HUnlock(paramPtr);

ADDING XCMD CODE RESOURCES TO THE .RSRC FILE

This can be done directly in THINK C 5.0 by using the merge option when building the code resource. For other versions of C use ResEdit to add the files.

DISCUSSION

Initially I was disturbed to discover I could not use some of the C library routines in XCMD’s which I eventually planned to use in standalone applications. Upon reflection, combined with some insights gained while writing the programs for this article, I finally decided that for me at least the problem was minor, if not non-existent.

The insights referred to above were the discovery that the inclusion of atoi increased the size of the XCMD from 3k to 10k. This is catatrophic if one hopes to write a large program which includes perhaps 100 XCMD’s. It is a nuisance with smaller routines.

The reflection says that the complete object code of a C library routine would have to be included in every XCMD which made use of it. The redundancy would quickly get out of hand.

The Toolbox and the SANE library have functions for almost everything that needs to be done in a program or code resource. This code is in the ROM and is always available for use without adding to the overhead. Portability considerations aside, it is desirable to take advantage of it whenever possible while writing Macintosh specific applications.

CONCLUSION

A practical method of using XCMD’s in standalone C applications was presented. An evaluation of the memory size problems encountered while developing this procedure would indicate that high-level lanquage library routines (C, Pascal, etc.) should be avoided in XCMD’s used by Hypercard as well as those written for standalone applications.

I can be reached on internet at ghkenner@cc.utah.edu, on Prodigy at BSSX14B and Apple Link at UUTL.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Ember 1.8.3 - Versatile digital scrapboo...
Ember (formerly LittleSnapper) is your digital scrapbook of things that inspire you: websites, photos, apps or other things. Just drag in images that you want to keep, organize them into relevant... Read more
Apple iTunes 12.1 - Manage your music, m...
Apple iTunes lets you organize and play digital music and video on your computer. It can automatically download new music, app, and book purchases across all your devices and computers. And it's a... Read more
LibreOffice 4.4.3 - Free, open-source of...
LibreOffice is an office suite (word processor, spreadsheet, presentations, drawing tool) compatible with other major office suites. The Document Foundation is coordinating development and... Read more
FoldersSynchronizer 4.2.1 - Synchronize...
FoldersSynchronizer is a popular and useful utility that synchronizes and backs-up files, folders, disks and boot disks. On each session you can apply special options like Timers, Multiple Folders,... Read more
Simon 4.0.2 - Monitor changes and crashe...
Simon monitors websites and alerts you of crashes and changes. Select pages to monitor, choose your alert options, and customize your settings. Simon does the rest. Keep a watchful eye on your... Read more
Cocktail 8.1.2 - General maintenance and...
Cocktail is a general purpose utility for OS X that lets you clean, repair and optimize your Mac. It is a powerful digital toolset that helps hundreds of thousands of Mac users around the world get... Read more
Cyberduck 4.6.4 - FTP and SFTP browser....
Cyberduck is a robust FTP/FTP-TLS/SFTP browser for the Mac whose lack of visual clutter and cleverly intuitive features make it easy to use. Support for external editors and system technologies such... Read more
Herald 5.0.2 - Notification plugin for M...
Note: Versions 2.1.3 (for OS X 10.7), 3.0.6 (for OS X 10.8), and 4.0.8 (for OS X 10.9) are no longer supported by the developer. Herald is a notification plugin for Mail.app, Apple's Mac OS X email... Read more
DEVONthink Pro 2.8.3 - Knowledge base, i...
Save 10% with our exclusive coupon code: MACUPDATE10 DEVONthink Pro is your essential assistant for today's world, where almost everything is digital. From shopping receipts to important research... Read more
Boom 2 1.0.1 - System-wide pro audio app...
Boom 2 is a system-wide volume booster and equalizer app that is designed especially for OS X 10.10 Yosemite. It comes with a smart interface, self-calibrates itself according to your Mac, offers... Read more

Playworld Superheroes Review
Playworld Superheroes Review By Tre Lawrence on January 30th, 2015 Our Rating: :: HERO CRAFTINGUniversal App - Designed for iPhone and iPad It’s all about the imagination, fighting bad creatures — and looking good while doing so.   | Read more »
Join the SpongeBob Bubble Party in this...
Join the SpongeBob Bubble Party in this New Match 3 Bubble Poppin’ Frenzy Posted by Jessica Fisher on January 30th, 2015 [ permalink ] | Read more »
Handpick Review
Handpick Review By Jennifer Allen on January 30th, 2015 Our Rating: :: TANTALIZING SUGGESTIONSiPhone App - Designed for the iPhone, compatible with the iPad Handpick will make you hungry, as well as inspire you to cook something... | Read more »
Storm the Halls of Echo Base in First St...
Storm the Halls of Echo Base in First Star Wars: Galactic Defense Event Posted by Jessica Fisher on January 30th, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Contradiction Review
Contradiction Review By Tre Lawrence on January 30th, 2015 Our Rating: :: SPOT THE LIEiPad Only App - Designed for the iPad Contradiction is a live action point and click adventure that’s pretty engaging.   Developer: Tim Follin... | Read more »
Unlock Sunshine Girl in Ironkill with th...
Unlock Sunshine Girl in Ironkill with this special 148Apps code Posted by Rob Rich on January 29th, 2015 [ permalink ] Robo-fighter Ironkill has been out on iOS a | Read more »
Crossroad Zombies Review
Crossroad Zombies Review By Jordan Minor on January 29th, 2015 Our Rating: :: CROSSWALKING DEADiPad Only App - Designed for the iPad Crossroad Zombies is a rough draft of a cool genre mash-up.   | Read more »
Blood Brothers 2 – Tips, Cheats, and Str...
War is hell: Is it the kind of hell you want to check out? Read our Blood Brothers 2 review to find out! Blood Brothers 2, DeNA’s follow-up to the original Blood Brothers, is an intriguing card collecting / role-playing / strategy hybrid. There’s... | Read more »
Blood Brothers 2 Review
Blood Brothers 2 Review By Nadia Oxford on January 29th, 2015 Our Rating: :: AN AGGRAVATING RELATIVEUniversal App - Designed for iPhone and iPad Blood Brothers 2 is built on a simple, solid foundation, but its free-to-play system... | Read more »
I AM BREAD, the Toast of the Town, is Ro...
Have you ever dreamt of being deliciously gluten-y? Do you feel passionate about Rye and Wheat? The guys at Bossa Studios do and that is why they are bringing I AM BREAD to iOS soon. The loafy app will feature all the new content that is being... | Read more »

Price Scanner via MacPrices.net

Intel Aims to Transform Workplace With 5th-Ge...
Intel Corporation today announced the availability of its 5th generation Intel Core vPro processor family that provides cutting-edge features to enable a new and rapidly shifting workplace. To meet... Read more
iOS App Sharalike Introduces New Instant Smar...
Sharalike slideshow and photo management software for iOS, is making it easier than ever to create shareable meaningful moments with its new instant SmartShow technology. Staying organized is a goal... Read more
Apple Becomes World’s Largest Smartphone Vend...
According to the latest research data from Strategy Analytics, as global smartphone shipments grew 31 percent annually to reach a record 380 million units in the fourth quarter of 2014. Apple became... Read more
Cut the Cord: OtterBox Resurgence Power Case...
Dead batteries and broken phones are two of the biggest issues for smartphone users today. Otterbox addresses both with the new Resurgence Power Case for Apple iPhone 6, promising to make those panic... Read more
13-inch Retina MacBook Pros on sale for up to...
B&H Photo has 13″ Retina MacBook Pros on sale for $200 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 2.6GHz/128GB Retina MacBook Pro: $1199.99 save $100 - 13″ 2.6GHz/... Read more
15-inch 2.5GHz Retina MacBook Pro on sale for...
 B&H Photo has the 15″ 2.5GHz Retina MacBook Pro on sale for $2319.99 including free shipping plus NY sales tax only. Their price is $180 off MSRP, and it’s the lowest price available for this... Read more
Back in stock: Refurbished iPod nanos for $99...
The Apple Store has Apple Certified Refurbished 16GB iPod nanos available for $99 including free shipping and Apple’s standard one-year warranty. That’s $50 off the cost of new nanos. Most colors are... Read more
Apple lowers price on refurbished 256GB MacBo...
The Apple Store has lowered prices on Apple Certified Refurbished 2014 MacBook Airs with 256GB SSDs, now available for up to $200 off the cost of new models. An Apple one-year warranty is included... Read more
New Good Management Suite Simplifies Enterpri...
Good Technology has announced the availability of the Good Management Suite, a comprehensive cross-platform solution for organizations getting started with mobile business initiatives. Built on the... Read more
15-inch 2.0GHz Retina MacBook Pro (refurbishe...
The Apple Store has Apple Certified Refurbished previous-generation 15″ 2.0GHz Retina MacBook Pros available for $1489 including free shipping plus Apple’s standard one-year warranty. Their price is... Read more

Jobs Board

*Apple* Solutions Consultant- Retail Sales (...
**Job Summary** The ASC is an Apple employee who serves as an Apple brand ambassador and influencer in a Reseller's store. The ASC's role is to grow Apple Read more
Event Director, *Apple* Retail Marketing -...
…This senior level position is responsible for leading and imagining the Apple Retail Team's global engagement strategy and team. Delivering an overarching brand Read more
At-Home Chat Specialist- *Apple* Online Stor...
**Job Summary** At Apple , we believe in hard work, a fun environment, and the kind of creativity and innovation that only comes about when talented people from diverse Read more
SW QA Engineer - *Apple* TV - Apple (United...
**Job Summary** The Apple TV team is looking for experienced Quality Assurance Engineers with a passion for delivering first in class home entertainment solutions. **Key Read more
*Apple* Retail - Multiple Positions(US) - Ap...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you re also the Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.