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

Logic Pro X 10.1.1 - Music creation and...
Apple Logic Pro X is the most advanced version of Logic ever. Sophisticated new tools for professional songwriting, editing, and mixing are built around a modern interface that's designed to get... Read more
VLC Media Player 2.2.0 - Popular multime...
VLC Media Player is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX, MP3, OGG, ...) as well as DVDs, VCDs, and various streaming protocols. It... Read more
Sound Studio 4.7.8 - Robust audio record...
Sound Studio lets you easily record and professionally edit audio on your Mac. Easily rip vinyls and digitize cassette tapes, or record lectures and voice memos. Prepare for live shows with live... Read more
LibreOffice 4.4.1.2 - Free, open-source...
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
Freeway Pro 7.0.3 - Drag-and-drop Web de...
Freeway Pro lets you build websites with speed and precision... without writing a line of code! With its user-oriented drag-and-drop interface, Freeway Pro helps you piece together the website of... Read more
Cloud 3.3.0 - File sharing from your men...
Cloud is simple file sharing for the Mac. Drag a file from your Mac to the CloudApp icon in the menubar and we take care of the rest. A link to the file will automatically be copied to your clipboard... Read more
Cyberduck 4.6.5 - 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
Firefox 36.0 - Fast, safe Web browser. (...
Firefox for Mac offers a fast, safe Web browsing experience. Browse quickly, securely, and effortlessly. With its industry-leading features, Firefox is the choice of Web development professionals and... Read more
Thunderbird 31.5.0 - Email client from M...
As of July 2012, Thunderbird has transitioned to a new governance model, with new features being developed by the broader free software and open source community, and security fixes and improvements... Read more
VOX 2.4 - Music player that supports man...
VoxIt just sounds better! The beauty is in its simplicity, yet behind the minimal exterior lies a powerful music player with a ton of features & support for all audio formats you should ever need... Read more

Get The Whole Story – Lone Wolf Complete...
Get The Whole Story – Lone Wolf Complete is Now Available and On Sale Posted by Jessica Fisher on February 27th, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Who Wore it Best? The Counting Dead vs....
Like it or not, the “clicker” genre, popularized by cute distractions like Candy Box and Cookie Clicker, seems like it’s here to stay. So Who Wore it Best? takes a look at two recent examples: The Counting Dead and AdVenture Capitalist. | Read more »
Card Crawl, the Mini Deck Building Game,...
Card Crawl, the Mini Deck Building Game, is Coming Soon Posted by Jessica Fisher on February 27th, 2015 [ permalink ] Tinytouchtales and Mexer have announced their new game, | Read more »
Witness an all new puzzle mechanic in Bl...
Well, BlastBall MAX is not one of those games and is bucking trends such as timers, elements of randomness, and tacked-on mechanics in favor of pure puzzle gameplay. When you first boot up the game you’ll see a grid made up of squares that are each... | Read more »
This Princess Has a Dragon and She isn’t...
This Princess Has a Dragon and She isn’t Afraid to Useit. | Read more »
Mecha Showdown Review
Mecha Showdown Review By Lee Hamlet on February 27th, 2015 Our Rating: :: IN A SPINUniversal App - Designed for iPhone and iPad Mecha Showdown replaces traditional buttons with a slot machine mechanic in this robot fighting game,... | Read more »
Reliance Games and Dreamworks Unveil Rea...
Reliance Games and Dreamworks Unveil Real Steel Champions Posted by Ellis Spice on February 27th, 2015 [ permalink ] Reliance Games and Dreamworks have announced that a third game in | Read more »
Sum Idea Review
Sum Idea Review By Jennifer Allen on February 27th, 2015 Our Rating: :: TAXING NUMBERSUniversal App - Designed for iPhone and iPad Sum Idea is a fairly charming but taxing puzzle game.   | Read more »
A New Badland Update Brings Daydream Lev...
A New Badland Update Brings Daydream Levels to Co-Op Posted by Ellis Spice on February 27th, 2015 [ permalink ] Universal App - Designed for iPhone and iPad | Read more »
Slashing Demons Review
Slashing Demons Review By Lee Hamlet on February 27th, 2015 Our Rating: :: IT'S A LONG WAY TO THE TOPUniversal App - Designed for iPhone and iPad Slashing Demons lacks the depth or scope to take it beyond the point of being just... | Read more »

Price Scanner via MacPrices.net

Save up to $600 with Apple refurbished Mac Pr...
The Apple Store is offering Apple Certified Refurbished Mac Pros for up to $600 off the cost of new models. An Apple one-year warranty is included with each Mac Pro, and shipping is free. The... Read more
Updated Mac Price Trackers
We’ve updated our Mac Price Trackers with the latest information on prices, bundles, and availability on systems from Apple’s authorized internet/catalog resellers: - 15″ MacBook Pros - 13″ MacBook... Read more
Apple CEO Tim Cook to Deliver 2015 George Was...
Apple CEO Tim Cook will deliver the George Washington University’s Commencement address to GWU grads on May 17, at which time he will also be awarded an honorary doctorate of public service from the... Read more
Apple restocks refurbished Mac minis for up t...
The Apple Store has restocked Apple Certified Refurbished 2014 Mac minis, with models available starting at $419. Apple’s one-year warranty is included with each mini, and shipping is free: - 1.4GHz... Read more
Save up to $50 on iPad Air 2s, NY tax only, f...
 B&H Photo has iPad Air 2s on sale for $50 off MSRP including free shipping plus NY sales tax only: - 16GB iPad Air 2 WiFi: $469.99 $30 off - 64GB iPad Air 2 WiFi: $549 $50 off - 128GB iPad Air 2... Read more
16GB iPad Air 2 on sale for $447, save $52
Walmart has the 16GB iPad Air 2 WiFi on sale for $446.99 on their online store for a limited time. Choose free shipping or free local store pickup (if available). Sale price for online orders only,... Read more
iMacs on sale for up to $205 off MSRP
B&H Photo has 21″ and 27″ iMacs on sale for up to $205 off MSRP including free shipping plus NY sales tax only: - 21″ 1.4GHz iMac: $1029 $70 off - 21″ 2.7GHz iMac: $1199 $100 off - 21″ 2.9GHz... Read more
Apple Takes 89 Percent Share of Global Smartp...
According to the latest research from Strategy Analytics, global smartphone operating profit reached US$21 billion in Q4 2014. The Android operating system captured a record-low 11 percent global... Read more
New Travel Health App “My Travel Health” iOS...
Rochester, Minnesota based Travel Health and Wellness LLC has announced that its new iOS app help safeguard the user’s health when traveling abroad — “My Travel Health” is now available on the Apple... Read more
Sale! MacBook Airs for up to $115 off MSRP
B&H Photo has MacBook Airs on sale for up to $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 128GB MacBook Air: $799 100 off MSRP - 11″ 256GB MacBook Air: $999 $100... Read more

Jobs Board

Sr. Technical Services Consultant, *Apple*...
**Job Summary** Apple Professional Services (APS) has an opening for a senior technical position that contributes to Apple 's efforts for strategic and transactional 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
*Apple* Pay - Site Reliability Engineer - Ap...
**Job Summary** Imagine what you could do here. At Apple , great ideas have a way of becoming great products, services, and customer experiences very quickly. Bring Read more
*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
*Apple* Solutions Consultant - Retail Sales...
**Job Summary** As an Apple Solutions Consultant (ASC) you are the link between our customers and our products. Your role is to drive the Apple business in a retail Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.