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Feb 96 Top 10
Volume Number:12
Issue Number:2
Column Tag:Symantec Top 10

Symantec Top 10

This monthly column, written by Symantec’s Technical Support Engineers, is intended to give our readers technical information on using Symantec products.

By Michael Hopkins, Symantec

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

Q: I am compiling my project with the THINK Project Manager and I get an error message "Error: Illegal Near Data". What can I do to correct this problem?

A: This typically occurs when you have Far DATA checked in the Project Options dialog box and not Far CODE. To turn on Far CODE, choose Set Project Type from the Project menu and check the Far CODE check box. For more information on how to use Far CODE and Far DATA, consult your User’s Guide.

Q: I have written some simple code that has a structure declaration in a header file and then a global variable of that structure type in my main source file. When I compile the code, I get the message "Error: Size of struct is not known". Furthermore, when I preprocess the file, I don’t see my struct declaration being included. What is going on?

A: Let’s take a look at an example:


/* main.c */ 
#include "timer.h"

struct clock local_clock;

main()
{
}


/*  timer.h  */
struct clock {
 long start_time;
 long end_time;
};

What is wrong with this picture? Well, there is actually nothing wrong with the structure. The problem is that Timer.h is the name of a system include file that is automatically included as part of the precompiled headers (in this case, MacHeaders). Therefore, the user header file is not being included because a system file of the same name is being used. To correct this problem, either rename the user header file or, for non-Macintosh applications, do not include MacHeaders in the prefix.

Q: I am writing a virus scanning program and I need to examine code resources of an application to verify that they are valid. What information does the Symantec Linker place in the first two bytes of the code resource?

A: For all CODE segments besides CODE 0, there is a code segment header. The THINK Linkers use the upper bit of this header to indicate a model Far CODE segment. The runtime loader resides in CODE 1 of the application and is the first piece of code executed. The loader loads and initializes the DATA and STRS, installs hooks for _LoadSeg, _UnloadSeg, and _ExitToShell traps, and calls the main program.

If the code is using a far model, the _LoadSeg and _UnloadSeg bottlenecks completely replace the standard segment loader. The standard 4-byte CODE segment header is interpreted differently to accommodate the larger jump table, so it is incompatible with the ROM segment loader. The header has the following format:

The R bit indicates that the segment has relocations which must be applied at runtime. These are stored in a CREL resource with the same resource ID as the CODE segment. The F bit is used to distinguish a far header from the standard header.

Be aware that this format is different from the header that MPW and Merowerks use as well as the CFM-68K header format.

Q: I am trying to use ODBC (Open DataBase Collaboration) with the THINK Project manager and I am getting a number of link errors. What library files to I need to add to use ODBC?

A: To use ODBC, you will need to include:

• MacTraps and MacTraps2

• LibraryManagerClient.o

• alloc_private.c

You will also need to write two additional functions (source is in THINK Reference under Embedded DefProc):

 Boolean TrapAvailable( short theTrap );
 void FlushCache( void );

If you are compiling one of the demos, you will need to write a stricmp:

 pascal short _stricmp( const char *s, const char *s2)
 { 
 return (short)strcmp(s, s2); 
 }

Q: I am making a 68K version of my PPC application and I’m getting a link error with numtostring() which is in TextUtils.h. On the PPC, this routine is in InterfaceLib.xcoff. Where is it on the 68K mac?

A: It is important to realize that the lower-case version of numtostring() is different than NumToString() which is in MacTraps. NumToString() returns a pascal-style Str255, and numtostring() returns a c-style string. To use the lower-case version with the THINK project manager, you will need to include Apple C Glue which is in Macintosh Libraries:68K Libraries from the Symantec C++ v8 Release 4 CD.

Q: Is there any way that I to make the Finder run Power Macintosh DebugServices when I launch the SPM?

A: No, but you could tell SPM to launch DebugServices on startup or shutdown. To run a script automatically when the Project Manager opens, record or write a script using the Script Editor. Save the script in the (Scripts) folder and name it “Startup”. Alternatively, if you want the script to run on exit from the Project manager, name it “Shutdown”.

Q: I’ve noticed that all native applications have a note in the “Get Info” window that says: “Memory requirements will decrease by xxxxK if virtual memory is turned on in the Memory control panel”. Won’t using virtual memory decrease my application performance?

A: No, not necessarily. In some cases the use of virtual memory on Power Macintoshes can actually increase the runtime performance of your application. When VM is not enabled on a Power PC, the application’s stack, heap, and all of its code fragments have to be loaded into the application’s partition. With VM on, only the stack and heap are loaded into the application’s partition. This reduces launch time and requirements for native programs. The Virtual Memory Manager will track your application’s code fragments and load them into the application’s partition only when they are needed. If done correctly, this won’t result in a noticeable performance penalty and the application will launch much more quickly. For more information, refer to Inside Macintosh: PowerPC System Software.

Q: How do I create a CustomTEHook on a PowerPC?

A: It is actually fairly straight-forward thanks to Apple’s Universal Headers. Create your hook procedure with the following signature:

 
 pascal unsigned short myTextWidthHookProc( 
 unsigned short  textLen, 
 unsigned short  textOffset,
 void * textBufferPtr,
 TEPtr  pTE, 
 TEHandle hTE
 );

Then create a routine descriptor and call TECustomHook like this:

 TextWidthHookUPP myUPP = 
 NewTextWidthHookProc( myTextWidthHookProc );
 TECustomHook( intTextWidthHook, &myUPP, myTE );


Q: I have noticed that there is a problem in CDialogText where cuts, copies and pastes are not reported to the supervisor of the CDialogText. Is there an easy way to fix this?

A: Yes, there is. Change the code for CDialogText::

DoCommand to:

 void CDialogText::DoCommand( long theCommand )
 {
 inherited::DoCommand( theCommand );

 switch( theCommand )
 {
 case cmdCut:
 case cmdPaste:
 case cmdClear:
 if (editable)
 BroadcastChange( dialogTextChanged, &ID );
 break;
 default:
 break;
 }
 }

Q: How do I force Visual Architect to re-generate all sources including the files that should only be generated once such as CMain and CApp?

A: Take the Source directory in your project folder and either rename it or move it to a different location. Remove all of your existing generated VA files from your project. When you choose Generate All from the Visual Architect, it will create a new source folder and generate all of the files and then add them to your project.

Special Thanks To

Levi Brown, Craig Conner, Rick Hartmann, Noah Lieberman, Andy McFarland, Scott Morrison, Phil Shapiro, Jeff Weeks, Kevin Quah

 
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