TweetFollow Us on Twitter

Feb 96 Tips
Volume Number:12
Issue Number:2
Column Tag:Tips & Tidbits

Tips & Tidbits

By Steve Sisak, Contributing Editor

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

An HGetState Gotcha

HGetState does not return a valid handle state when you pass it an empty handle (one whose master pointer is NULL). Instead, it returns an error code, so before you call HGetState, be sure to check that the handle isn’t empty and execute an alternate code path if it is.

I was bitten by this because I was using HGetState to determine if a handle was to a resource, and the resource had been purged, so HGetState returned an error code instead of the handle flags, and I incorrectly decoded the return result and thought the handle wasn’t to a resource.

Eric Schlegel

From Inside Macintosh:
Memory, page 1-61 to 1-62:

If an error occurs during an attempt to get the state flags of the specified relocatable block, HGetState returns the low-order byte of the result code as its function result. For example, if the handle h points to a master pointer whose value is NIL, then the signed byutle returned by HGetState will contain the value -109.

Result codes:

noErr 0

nilHandleErr -109 NIL master pointer

memWZErr -111 Attempt to operate on a free block

An Old Bug, Turns Out to be “An Old Bug”

I think I found a bug in a Tip in the March 1995 issue of MacTech magazine. The Tip, entitled “Hot Tip for Hot Keys”, can be found on page 67. Allow me to quote a segment of code:

else
{
   num = CountDITL(theDialog);
   for(i=0; i<num; i++)
   {
        GetDItem(theDialog, i, &iType, &iHandle, &iRect);

                  //and so on ... the omitted code works wonderfully!
   }
}

The problem is that the for loop is counting from 0 to Number-Of-DITL-Items minus 1. While the for loop is executed the correct number of times, it’s starting and ending one index too early. This off-by-one error is relatively common in C. Either the for loop should be:

   for (i=1; i<=num; i++)

or the next line should read:

      GetDItem(theDialog, i + 1, &iType, &iHandle, &iRect);

This error is a little hard to detect. Calling GetDItem with itemNo set to 0 doesn’t cause any harm. The only effect this bug has is the final entry in the DITL isn’t included in the search. This final item usually isn’t a push button, so the author didn’t notice the error in his own routine. Otherwise, this code works wonderfully; I use a repaired version all the time!

Mike Trent

A More General Context Sensitive Cursor

In the December issue of MacTech, a technique for making your application WindowShade-savvy was presented, which checked the current content region of the window to see if it was null. A more general method for setting the cursor, which works for WindowShade as well as handling the cases of the cursor outside of the window and when the cursor is in a floating window over the active window is:

   GetMouse(&mouseLoc);
   if (!PtInRgn(mouseLoc,theWindow->visRgn))  
 // theWindow is the current window
   {
                        // Cursor is not in visible region of the window
                  // Set cursor to default arrow.
      InitCursor();
   }
   else
   {
                  // Adjust the cursor to the proper shape
   }

Paul Hyman

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Spotify 1.0.49.125. - Stream music, crea...
Spotify is a streaming music service that gives you on-demand access to millions of songs. Whether you like driving rock, silky R&B, or grandiose classical music, Spotify's massive catalogue puts... Read more
Eye Candy 7.2.0.50 - 30 professional Pho...
Eye Candy renders realistic effects that are difficult or impossible to achieve in Photoshop alone, such as Fire, Chrome, and the new Lightning. Effects like Animal Fur, Smoke, and Reptile Skin are... Read more
Safari Technology Preview 10.2 - The new...
Safari Technology Preview contains the most recent additions and improvements to WebKit and the latest advances in Safari web technologies. And once installed, you will receive notifications of... Read more
Microsoft Office 2016 15.31 - Popular pr...
Microsoft Office 2016 - Unmistakably Office, designed for Mac. The new versions of Word, Excel, PowerPoint, Outlook and OneNote provide the best of both worlds for Mac users - the familiar Office... Read more
QuickBooks 16.1.12.1564 R13 - Financial...
QuickBooks helps you manage your business easily and efficiently. Organize your finances all in one place, track money going in and out of your business, and spot areas where you can save. Built for... Read more
1Password 6.6.1 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
1Password 6.6.1 - Powerful password mana...
1Password is a password manager that uniquely brings you both security and convenience. It is the only program that provides anti-phishing protection and goes beyond password management by adding Web... Read more
Safari Technology Preview 10.2 - The new...
Safari Technology Preview contains the most recent additions and improvements to WebKit and the latest advances in Safari web technologies. And once installed, you will receive notifications of... Read more
Eye Candy 7.2.0.50 - 30 professional Pho...
Eye Candy renders realistic effects that are difficult or impossible to achieve in Photoshop alone, such as Fire, Chrome, and the new Lightning. Effects like Animal Fur, Smoke, and Reptile Skin are... Read more
Microsoft Office 2016 15.31 - Popular pr...
Microsoft Office 2016 - Unmistakably Office, designed for Mac. The new versions of Word, Excel, PowerPoint, Outlook and OneNote provide the best of both worlds for Mac users - the familiar Office... Read more

Tavern Guardians (Games)
Tavern Guardians 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: Tavern Guardians is a Hack-and-Slash action game played in the style of a match-three. You can experience high pace action... | Read more »
Slay your way to glory in idle RPG Endle...
It’s a golden age for idle games on the mobile market, and those addictive little clickers have a new best friend. South Korean developer Ekkorr released Endless Frontier last year, and players have been idling away the hours in the company of its... | Read more »
Tiny Striker: World Football Guide - How...
| Read more »
Good news everyone! Futurama: Worlds of...
Futurama is finding a new home on mobile in TinyCo and Fox Interactive's new game, Futurama: Worlds of Tomorrow. They're really doing it up, bringing on board Futurama creator Matt Groening along with the original cast and writers. TinyCo wants... | Read more »
MUL.MASH.TAB.BA.GAL.GAL (Games)
MUL.MASH.TAB.BA.GAL.GAL 1.0 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0 (iTunes) Description: ENDLESS UPGRADES. CONSTANT DANGER. ANCIENT WISDOM. BOUNCY BALLS. Launch Sale, 40% OFF for a very limited time!!! MUL.... | Read more »
Dungeon Rushers (Games)
Dungeon Rushers 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: Dungeon Rushers is a 2D tactical RPG combining dungeon crawler’s gameplay and turn based fights. Manage your team, loot dusty... | Read more »
Blasty Bubs is a colorful Pinball and Br...
QuickByte Games has another arcade treat in the works -- this time it's a mishmash of brick breaking and Pinball mechanics. It's called Blasty Bubs, and it's a top down brickbreaker that has you slinging balls around a board. [Read more] | Read more »
Corsola and Heracross are the new region...
Generation 2 finally launched in Pokémon GO, unleashing a brand new batch of Pokémon into the wild. Even before the update went live people were speculating on how to catch elusive Pokémon like the legendary "dogs", Unknown, and whether or not... | Read more »
The Warlock of Firetop Mountain (Games)
The Warlock of Firetop Mountain 1.0 Device: iOS Universal Category: Games Price: $4.99, Version: 1.0 (iTunes) Description: An epic adventure through a mysterious mountain filled with monsters, magic and mayhem! “...it looks downright... | Read more »
Fantasy MMORPG MU Origin’s receives a hu...
Developer Webzen are looking to take their highly popular fantasy battler MU Origin to the next level this month, with its most ambitious overhaul yet. The latest update introduces the long sought after Server Arena, new treasure dungeons, and much... | Read more »

Price Scanner via MacPrices.net

Apple restocks refurbished 11-inch MacBook Ai...
Apple has Certified Refurbished 11″ MacBook Airs (the latest models recently discontinued by Apple), available for up to $170 off original MSRP. An Apple one-year warranty is included with each... Read more
Apple Park Opens to Employees in April With T...
Apple has announced that Apple Park, the company’s new 175-acre campus, will be ready for employees to begin occupying in April. The process of moving more than 12,000 people will take over six... Read more
Manhattan Neighbors for Safer Telecommunicati...
A new education and advocacy group focused on cell phone and wireless risks, Manhattan Neighbors for Safer Telecommunications, launched today at http://www.ManhattanNeighbors.org. Manhattan... Read more
Portable Dual DisplayPort Monitor Dock Enable...
IOGEAR has announced the launch of its USB-C Dual DisplayPort Monitor Portable Dock (GUC3CMST). The dock enables users to easily connect two DisplayPort monitors to a USB-C or Thunderbolt 3 laptop to... Read more
13-inch 2.7GHz Retina MacBook Pro on sale for...
Amazon.com has restocked the 13″ 2.7GHz/128GB Retina MacBook Pro (MF839LL/A) for $200 off MSRP including free shipping: - 13″ 2.7GHz/128GB Retina MacBook Pro: $1099 $200 off MSRP This model tends to... Read more
Apple’s New iPad Ads Don’t Address Pro Users’...
Apple launched a new tranche of iPad Pro TV ads last week addressing actual queries and challenges from the Twitterverse, albeit using actors for the visuals. That’s great. As an iPad fan and heavy... Read more
Free Verbum Catholic Bible Study App For iOS
The Verbum mobile app runs on Logos’ powerful Bible software and is an advanced resource for mobile Catholic study. The Verbum app surrounds the Bible with the Tradition. Verbum comes with 15 free... Read more
27-inch Apple iMacs on sale for up to $200 of...
B&H Photo has 27″ Apple iMacs on sale for up to $200 off MSRP, each including free shipping plus NY sales tax only: - 27″ 3.3GHz iMac 5K: $2099.99 $200 off MSRP - 27″ 3.2GHz/1TB Fusion iMac 5K: $... Read more
15-inch 2.2GHz Retina MacBook Pro on sale for...
Amazon has 2015 15″ 2.2GHz Retina MacBook Pros (MJLQ2LL/A) available for $1849.99 including free shipping. Apple charges $1999 for this model, so Amazon’s price is represents a $150 savings. Read more
Apple refurbished iPad Air 2s available start...
Apple has Certified Refurbished iPad Air 2 WiFis available for starting at $319 including free shipping. A standard Apple one-year warranty is included: - 16GB iPad Air 2 WiFi: $319 $60 off original... Read more

Jobs Board

Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
*Apple* Retail - Multiple Positions - Apple,...
Job Description: Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, Read more
Manager *Apple* Systems Administration - Pu...
Req ID 3315BR Position Title Manager, Apple Systems Administration Job Description The Manager of Apple Systems Administration oversees the administration and Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.