All Databases MacTech Vol 09-1993

Nov 93 Tips, Tidbits

Volume Number: 9

Issue Number: 11

Column Tag: Tips & Tidbits

Tips & Tidbits

By Neil Ticktin, Editor-in-Chief

Tip of the Month

In the September, 1993 issue of MacTech Magazine, one reader wrote in asking

about finding out if QuickTime is installed via the Gestalt call. We asked you, the

readers, to respond and you a number of you did. Thanks to all of you who responded

including: Gary Woodcock, Gary McGath and Mats Hummel who were among the first to

respond.

The first answer came from Robert Howe with a nice “clean” answer. The most

interesting answer came from Alain Danteny who not only answered this question, but

more about Gestalt. Robert and Alain are splitting this month’s prize.

First, the direct answer from Robert Howe: There is a new gestalt selector. You

can modify your GestaltEqu.h file (with Think C) to include the following:

/* 1 */
#define gestaltQuickTime 'qtim'

(Realize that this may be included in the new header files that come with the

THINK C 6.0.1 update). You may then call it as you would any other gestalt call. If

QuickTime is not installed, gestalt returns an error.

A quick boolean check could be written as

/* 2 */
#include 
if (QuickTimeInstalled());
     // play a movie
Boolean QuickTimeInstalled ( void ) {
     return (noErr == gestalt('qtim', &result));
}

- Robert Howe,

via America Online

More Gestalt information

Next, comes the additional information from Alain Danteny. If you want to have a

full view of all currently installed and registered gestaltSelectors, follow these steps:

First, call Gestalt with selector "tabl". The response (a pointer) is the starting

address of an array containing all the gestaltSelector and procAddress. The format of

each entry is:

{ 3 }
gestaltTableEntry = RECORD
      gestaltSelector : OSType;
      gestaltAddr : LongInt;
    END; {Pascal-like}

/* 4 */
struct{
    OSType gestaltSelector;
    long gestaltAddr;
}gestaltTableEntry;//C-like

The very first 2 entries are:

0000 000C xxxx xxxx ; (selector = $0000 000C in hexa)

0000 0007 yyyy yyyy ;

Those are undoubtly the selectors of Gestalt's developers at Apple: Carl C. Hewitt

and . Moreover, under macsbug, if you type:

ip xxxx xxxx (see above)

you will decompile the gestaltProc and see that those selectors are probably used

internaly by the traps Gestalt, NewGestalt, ReplaceGestalt... the gestaltProc uses two

signatures: "carl" and "bbmc" (who's bbmc?)

Following entries are non-Apple gestaltSelectors: mainly INITS and cdev

signatures (ADex, ADrk, MClk, NowTaso). Last are well-known Apple's system

Selectors. This array ends up with longint $7FFF FFFF.

- Alain Danteny,

Nancy, France

MOVEM.L Warning!

The MOVEM is a 680x0 assembler instruction. It is used a lot for saving and

restoring the values of multiple data and address registers. I tried to save off two

address register values with the lower register first and then restoring it later using

two MOVE.L instructions. I ran into an unexpected surprise. The instruction:

MOVEM.L A2/A4,-(A7)

is not equivalent as you would expect to the 2 instructions:

MOVE.L A2,-(A7)

MOVE.L A4,-(A7)

but instead to:

MOVE.L A4,-(A7)

MOVE.L A2,-(A7)

The instruction MOVEM.L stores the registers from high to low, ignoring the

order you specify. In other words,

MOVEM.L A2/A4,-(A7)

does the same thing as:

MOVEM.L A4/A2,-(A7)

Using MOVEM pre-decriment, -(A7), in conjunction with MOVEM

postincrement, (A7)+, addressing, saving off and restoring the same registers is what

the instruction was apparently designed for and works just fine for that purpose.

- Marek Hajek

Hajek’s Solutions

Reno, Nevada

Toggle invisibles in MPW

I often need to see “invisible” characters in text files, because many of mine

come from BBS captures and may have glitches in them. MPW’s sequence for turning

the display of invisible characters on and off is cumbersome, so I added a menu and

keyboard shortcut; a single command to toggle the display. The following command adds

a “Toggle Invisibles” to the Edit menu, so Command-Option-Y (displayed as ¥,

option-Y) does the trick.

/* 5 */
AddMenu Edit "Toggle Invisibles/¥" ∂
 'If `Format -x a "{Active}"` == "Ail" ; ∂
   Format -a AIl "{Active}" ; ∂
  Else ; ∂
   Format -a Ail "{Active}" ; ∂
  End'

What this does: The first Format command, `Format -x a "{Active}"`, emits a

string describing the active window’s format attributes. The If statement compares

this to a default string of “Ail”: “A” for Auto-indent on, “i” for invisibles off, and

“l” for lock-scroll off. Based on the result of that comparison, another Format

command is issued to turn the display of invisible characters on or off (Format -a AIl

or Format -ia Ail, respectively).

The format attribute strings “Ail” and “AIl” assume the other defaults for the

file format attributes are Auto-indent ON and lock-scroll OFF. These are the common

defaults, but you can change them by switching the case of the A and L in the format

command. For example, if you prefer to not auto-indent, the format attribute strings

would be “ail” and “aIl” instead.

- Lee David Rimar

Absoft Corporation

Need information on your Macintosh?

Need some extensive information about your Mac? In AppleLink, press Option -

Command - D.

- William Modesitt

Maui Software

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