Using Gestalts in RB
By Dan Vanderkam
Note: 2.0.1a2 or later is needed to use this article.
No, it's not just a funny word. Gestalts are a way that a program can ask for certain info about a computer from the system. For example, you could get the version of QuickTime, or the system bus's clock speed using Gestalts. They're quite useful.
To access Gestalts, RB uses a simple method: System.Gestalt. This function returns a boolean (indicating whether the gestalt exists or not), and it takes two parameters: the four letter code of the gestalt, and an integer that will contain the info.
For example, to get the clock speed of the computer, we might use this code:
Dim speed as integer
if System.Gestalt("pclk", speed) then
msgbox "Your system runs at "+str(speed)+" Hertz."
else
msgbox "Something is seriously bizarre with your computer."
End if
When I run this code, RB displays the message "Your system runs at 2.40000000e+8 Hertz." If you multiply out that number, you'll find that it's 240 million. 240 million Hertz is 240Mhz, which is what my computer runs at.
However, the numbers that are given by System.Gestalt aren't always so nice. Many Gestalts return a version number. For example, if we replaced System.Gestalt("pclk", speed) with System.Gestalt("qtim", speed), we'd be told that the QuickTime version is 67133473. Oddly enough, this number represents Quicktime 4.0.0. However, we we convert this number into hexadecimal, things become clearer. In hex, this number is 4006021. So, the first number of the version in Hex is the major release. The second is the minor release, and the third is the maintenance release number. So, this routine should tell us the version of QuickTime in ordinary english:
Dim Version as integer, vers as string
dim major, minor, maint as string
if System.Gestalt("qtim",version) then
vers=hex(version)
major=mid(vers, 1, 1)
minor=mid(vers, 2, 1)
maint=mid(vers, 3, 1)
MsgBox "QuickTime version is "+major+"."+minor+"."+maint+"."
else
MsgBox "QuickTime isn't installed."
end if
That system for using versions isn't true only for QuickTime. It also works for almost anything else that returns a version.
Now that you know how to use a Gestalt in your program, here's a list of codes you might want to try:
| Code | Description | |||||||||||||||
| qtim | Returns the QuickTime version | |||||||||||||||
| ag_v | Returns the version of AppleGuide (if it's present) | |||||||||||||||
| appr | Appearance manager. Returns 1 if it's there, 0 if it's not. | |||||||||||||||
| apvr | Returns Appearance Manager version. | |||||||||||||||
| ascr/ascv | AppleScript present/version number | |||||||||||||||
| cash | The amount of RAM given to the disk cache (in bytes) | |||||||||||||||
| cmnu | The Gestalt function returns true if contextual menus are installed, false if they're not. | |||||||||||||||
| cpkr | Returns the color picker version. | |||||||||||||||
| doub | Returns the version of WorldScript (if installed) | |||||||||||||||
| dkpx | Returns the version of the Desktop Pictures control panel (if installed) | |||||||||||||||
| micn | Returns the computer's icon family ID. All icons are generic after System 7.5 | |||||||||||||||
| nvsv | Gestalt returns true if NavServices are present, false if they aren't | |||||||||||||||
| otvr | Returns the Open Transport version. | |||||||||||||||
| thds | Gestalt returns true if the Thread Manager is present, false if it isn't. | |||||||||||||||
|
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| usb | Gestalt returns true if USB abilities are available, false if they aren't. | |||||||||||||||
| rom | Returns the amount of ROM in bytes. | |||||||||||||||
| pclk | Returns the processor speed in Hertz (1,000,000 Hz=1Mhz) | |||||||||||||||
| mach | Returns the machine type (ie, PowerBook 3400c). Look this up for machine types. | |||||||||||||||
| ram /lram | The amount of RAM/Logical RAM (in bytes) | |||||||||||||||
| fpu | Returns 0 if no FPU, higher than that if there is. Be sure to write 'fpu ' | |||||||||||||||
| bclk | Returns the bus speed in Hertz (1,000,000 Hz=1 Mhz) | |||||||||||||||
| cput | Returns the CPU type as a special number:
|
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For a much more complete list of codes, check out the Gestalt Selectors List 4.3.2 Overview page, which has a comprehensive list of all the known four letter gestalt codes. The table I've included here is just a small helping of what's on that page. Enjoy!