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

How to become the ultimate robot warrior...
Chrono Strike is a delightfully immersive beat ‘em up with a sense of humor (any game with a good Sims reference gets points in my book). [Read more] | Read more »
Tips and tricks to get a higher score in...
Snow Roll is a devilish endless runner very much in the vein of Flappy Bird. It revels in its dastardly level of difficulty, and doesn’t really care how angry you get at it as it knows you’ll keep coming back for more. [Read more] | Read more »
How to win big in Slots Deluxe
Cheating while gambling is illegal and morally wrong, and in some parts of the world it leads to men with names like Vinnie "Six Knuckles" Manchenzo beating you to a pulp in a dark alley. [Read more] | Read more »
How to take over the world in Dictator 2
Running a country isn't easy - especially when you're a dictator who wants to take over the world and crush everyone in your path while you do it. [Read more] | Read more »
Tips and tricks to get a higher score in...
Tank.iois - you guessed it! - another multiplayer arena battler likeAgar.io and Slither.io. It does differentiate itself by putting you in a tiny tank though, so it's not exactly the same. To help you get that all-important high score, we've got a... | Read more »
How to unlock characters in One Tap Tenn...
As the title suggests, One Tap Tennis requires only a single tap to play its particular brand of tennis, and rewards you with a ton of unlockable characters if you perform well. Fortunately for you, we at 148Apps have got a few tips and tricks to... | Read more »
Grab it now: Game Craft’s Legend of War...
The real time strategy game is now available for you to sink your teeth into, through the App Store and Google Play. Combining elements of skill, strategy and empire building, Legend of War is a real gamers’ game. [Read more] | Read more »
Skateboard Party 3 ft. Greg Lutzka (Gam...
Skateboard Party 3 ft. Greg Lutzka 1.0 Device: iOS Universal Category: Games Price: $1.99, Version: 1.0 (iTunes) Description: Skateboard Party is back! This third edition of the popular sports franchise features professional skater... | Read more »
Cubious (Games)
Cubious 1.0 Device: iOS Universal Category: Games Price: $.99, Version: 1.0 (iTunes) Description: Cubious – How smart are you? How high is your IQube? Solve the impossible puzzles to find out, and help a lost little cube find his... | Read more »
Goat Simulator Waste of Space (Games)
Goat Simulator Waste of Space 1.1 Device: iOS Universal Category: Games Price: $4.99, Version: 1.1 (iTunes) Description: ** IMPORTANT - SUPPORTED DEVICESiPhone 4S, iPad 2, iPod Touch 5 or better.** | Read more »

Price Scanner via MacPrices.net

Enterprise Workers Pick Technology Over Perks...
New Adobe study shows surprising attitudes about office jobs and where the future of work is heading. Adobe has released survey findings revealing that a surprising 70 percent of U.S. office workers... Read more
Memorial Day Weekend Sale: $50-$100 off 11-in...
B&H Photo has 13″ and 11″ MacBook Airs with 256GB SSDs on sale for $50-$100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 1.6GHz/256GB MacBook Air: $999 $100 off MSRP... Read more
Memorial Day Weekend Sales: Apple MacBook Pro...
B&H Photo has 13″ and 15″ Retina MacBook Pros on sale for up to $210 off MSRP. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina MacBook Pro: $1799 $200 off MSRP - 15″ 2.5GHz... Read more
Memorial Day Weekend Sales: Apple iMacs and M...
Take up to $150 off the price of a new iMac or Mac mini at the following Apple resellers this Memorial Day weekend: iMacs: B&H Photo has 21″ and 27″ iMacs on sale for up to $150 off MSRP... Read more
Apple refurbished Retina MacBook Pros availab...
Apple has Certified Refurbished 2015 13″ and 15″ Retina MacBook Pros available for up to $380 off the cost of new models. An Apple one-year warranty is included with each model, and shipping is free... Read more
Apple refurbished 11-inch MacBook Airs availa...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models), available for up to $170 off the cost of new models. An Apple one-year warranty is included with each MacBook, and shipping is... Read more
Goal Zero and OtterBox Partner to Expand iPh...
Goal Zero, specialists in portable power, have announced a partnership with OtterBox, brand smartphone case protection, to offer the Slide and Slide Plus Batteries as modules compatible with the new... Read more
15-inch Retina MacBook Pros on sale for up to...
B&H Photo has 15″ Retina MacBook Pros on sale for up to $210 off MSRP. Shipping is free, and B&H charges NY tax only: - 15″ 2.2GHz Retina MacBook Pro: $1799 $200 off MSRP - 15″ 2.5GHz Retina... Read more
Clearance 2015 13-inch MacBook Airs available...
B&H Photo has clearance 2015 13″ MacBook Airs available for $250 off original MSRP. Shipping is free, and B&H charges NY sales tax only: - 13″ 1.6GHz/4GB/128GB MacBook Air (MJVE2LL/A): $799... Read more
Apple refurbished Apple TVs available for up...
Apple has Certified Refurbished 32GB and 64GB Apple TVs available for up to $30 off the cost of new models. Apple’s standard one-year warranty is included with each model, and shipping is free: -... Read more

Jobs Board

*Apple* Architect - AECOM (United States)
**Requisition/Vacancy No.** 132759BR **Position Title** Apple Architect **Job Category** Information Technology **Business Line** Government **Country** United Read more
*Apple* Solutions Consultant - APPLE (United...
Job Summary As an Apple Solutions Consultant, you'll be the link between our future customers and our products. You'll showcase your entrepreneurial spirit as you Read more
*Apple* Project Engineer - Smart Source Inc...
SmartSource is in need of an Apple Project Engineer for a 12 month contract opportunity in Pittsburg, PA. Role: Apple Project Engineer Location: Pittsburg, PA Read more
Automotive Sales Consultant - Apple Ford Linc...
…you. The best candidates are smart, technologically savvy and are customer focused. Apple Ford Lincoln Apple Valley is different, because: $30,000 annual salary Read more
Service Assistant - *Apple* Chevrolet *App...
Apple Automotive is one of the fastest growing dealer...and it shows. Consider making the switch to the Apple Automotive Group today! At Apple Automotive, we Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.