TweetFollow Us on Twitter

Doodats
Volume Number:5
Issue Number:9
Column Tag:C Workshop

Three Doodats

By Lee A. Neuse, Manassas, VA

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

[Lee Neuse started in the days you built them before programmed them. He was lured away from IBM compatibles to the Mac in 1982 and been there ever since. Currently, he is working for Computer Science Corporation designing and implementing Mac software as part of CSC research. His Mousehole handle is "Noisy".]

Three Doodats

Doodat -- a trivial problem guaranteed to make a programmer’s life miserable; from the expression “How did he do dat?”.

It seems like every programmer, at one time or another, is faced with the same dilemma: wanting to use a feature in a program, but not wanting to spend the time to figure out the technique. For example, we all know that a Balanced B-Tree index is wonderfully efficient, but how many of us really want to sit down and write the code? One solution is to start reading back issues of MacTutor, hoping that some kind soul has already published useable source code. Another is to scour public domain software for an author willing to impart knowledge in exchange for a shareware donation. Either way, it’s usually faster (and easier) to find and adapt someone else’s code instead of doing it yourself.

The purpose of ‘Doodats’ is to provide generic solutions to the little problems, so the programmer can spend his or her time working on the big problems (like what the program does).

Doodat #1

Problem: how to determine if the user has tried to abort something by pressing the Cmd-’.’ keys. EventAvail() returns only the first keystroke event in the queue, and the user may have pressed some other keys since the last keystroke event was read by the application. Either GetNextEvent() or WaitNextEvent() return all keystroke events, forcing the application to store them or ignore them (a Bad Thing). Moreover, if MultiFinder is running, calling any of these event-related traps may cause the application to be switched out, which could cause problems.

Solution: Doodat #1 is a routine called check_abort(), which directly scans the ToolBox’s internal event queue for Cmd-’.’ abort events.

The routine starts by setting a pointer to head of the event queue (stored in the system global EventQueue), then examining the next event in the queue. If the event is a Cmd-’.’ event, it is removed by calling Dequeue(), and the ‘found’ flag set. If the pointer does not match the event queue tail, it is advanced to the next event, otherwise, the function returns. This technique solves all of the problems posed by normal event processing:

1. It doesn’t affect any other keystroke events in the queue.

2. If the user has generated multiple aborts (by holding the keys down), it removes all of them.

3. It does not call EventAvail() or WaitNextEvent(), so no chance of being switched in or out under MultiFinder.

To use check_abort(), call it from within any place where the user might want to abort. For example:

/* 1 */

for (page = 1; page < last_page; page++)
 {
 /* print a page */
 if (check_abort())
 break;
 }

/*************************************************
**
** check_abort() - Lightspeed C Version
**
** This routine returns scans the low-level
** event queue in search of a Cmd-’.’ key event
** Each one found is removed from the event
** queue.
**
** In:  N/A
**
** Out: TRUE if Cmd-’.’ found, FALSE otherwise.
**
*/

Boolean
check_abort()
{
EvQElPtreq_p;
Boolean f_found = false;

/* start at head of internal queue */
eq_p = (EvQElPtr)(EventQueue.qHead);

while (true)
 {
 if ((eq_p->evtQWhat == keyDown ||
 (eq_p->evtQWhat == autoKey) &&
 (eq_p->evtQModifiers & cmdKey) &&
 (eq_p->evtQMessage & charCodeMask) == ‘.’)
 {
/* remove the event from the queue */
 Dequeue((QElemPtr)eq_p, &EventQueue);
 f_found = true;
 }
/* test for end of queue */
 if (eq_p == (EvQElPtr)EventQueue.qTail)
 break;

/* continue with next queue entry */
 eq_p = (EvQEl *)(eq_p->qLink);
 }
return(f_found);
}/* end of check_abort() */

Doodat #2

Problem: Many windows contain items such as lines, icons, pictures, or text strings that are there for decoration; these items don’t change in appearance, and clicking on them has no effect. While the code to draw these items is relatively simple, it is also very boring to write, and frequently quite lengthy. In addition, trying to figure out exactly which horizontal and vertical co-ordinates to use can be time-consuming and frustrating.

Solution: Doodat #2 is an attempt to save time (and code!) by making ResEdit and the Resource Manager do most of the work. This involves a two-step approach:

Step 1 is to use ResEdit (or any other Resource tool) to create a ‘DITL’ resource (Dialog Item List) that contains all of the items desired. ResEdit is particularly handy, as the items can be arranged visually within the window. The DITL resource may be created and edited normally, with all items being set to disabled. No Control or EditText items should be included (they will be ignored if you do), and the items may be in any order. The finished DITL resource is then included in the application’s resources for later use.

UserItems in the item list are handled in one of two ways: either as a dividing line or as frame. If the horizontal or vertical co-ordinates are equal, i.e. the boundary rectangle is empty, it is drawn as a 50% gray line. If the rectangle is not empty, it is drawn as a black frame.

Text items are drawn (left-justified) in whatever font the window’s port is using when draw_ditl() is called. Different text characteristics could be supplied by reserving the first few characters of the text string but that’s for another time.

Step 2 is to use the routine below called draw_ditl() to actually read in and draw the items within the window. This routine accepts the ID number of a DITL resource, reads the resource into memory, then traverses the item list, drawing each item accordingly. For draw_ditl() to work properly, the DITL resource must be present in the application’s resource fork (or in an open resource file), and the port set to the desired window.

draw_ditl() uses the following definitions and structure:

/* 2 */

#define NIL 0L

/* Test a pointer for validity */
#define VALID_PTR(p) ((long)(p) &&
 ((long)(p) & 1L) == NIL)

/* Test a handle for validity */
#define VALID_HNDL(h)(VALID_PTR(h) &&
 VALID_PTR((long)(*(h)) & 0x00FFFFFF))

typedef struct
 {
 Handle hndl;
 Rect   frame;
 unsigned char   type;
 unsigned char   length;
 short  data[];
 } ditl_list;

/*************************************************
**
** draw_ditl() - Lightspeed C Version
**
** This routine reads in and draws the items in a
** Dialog Item List (DITL) resource.
**
** In:  resource id of DITL
**
** Out: N/A
**
*/

void
draw_ditl(ditl_id)
short   ditl_id;
{
Handle  ditl_h;
ditl_list *ditl_p;
PenStatesave_pen;
short   d_type, offset, num_items;

ditl_h = GetResource(‘DITL’, ditl_id);
if (ResError() != noErr || !VALID_HNDL(ditl_h))
 return;

HLock(ditl_h);
/* don’t change pen behind the window’s back */
GetPenState(&save_pen);
PenNormal();
/* get the number of items in list */
num_items = *((short *)(*ditl_h)) + 1;
/* set pointer to first item in list */
ditl_p = (ditl_list *)((*ditl_h) + sizeof(short));
while  (num_items--)
 {
/* mask out the item disabled bit */
 switch (ditl_p->type & 0x7F)
 {
 case statText:
 TextBox((char *)ditl_p->data,
 ditl_p->length, &(ditl_p->frame),
 teJustLeft);
 break;
 
 case iconItem:
 ditl_p->hndl =
 GetIcon(ditl_p->data[0]);
 if (VALID_HNDL(ditl_p->hndl))
 {
 PlotIcon(&(ditl_p->frame),
 ditl_p->hndl);
 ReleaseResource(ditl_p->hndl);
 }
 break;
 
 case picItem:
 ditl_p->hndl = GetResource(‘PICT’,
 ditl_p->data[0]);
 if (VALID_HNDL(ditl_p->hndl))
 {
 DrawPicture((PicHandle)ditl_p->hndl,
 &(ditl_p->frame));
 ReleaseReource(ditl_p->hndl);
 }
 break;
 
 case userItem:
 if (EmptyRect(&(ditl_p->frame)))
 {
 PenPat(gray);
 MoveTo(ditl_p->frame.left,
 ditl_p->frame.top);
 LineTo(ditl_p->frame.right,
 ditl_p->frame.bottom);
 PenPat(black);
 }
 else
 FrameRect(&(ditl_p->frame));
 break;
 }
/* force offset to a word (even) boundary */
 if ((offset = ditl_p->length) & 1)
 offset++;
/* advance pointer to next item */
 ditl_p = (ditl_list *)((char *)ditl_p +
 sizeof(ditl_list) + offset);
 }

HUnlock(ditl_h);
ReleaseResource(ditl_h);
/* restore pen to original condition */
SetPenState(&save_pen);
}/* end of draw_ditl() */

Doodat #3

Problem: Sooner or later, an application is going to need to access a data file of some sort, with fixed-length or variable-length records, keys, and so forth. Using the Resource Manager as a Poor Man’s Database is a Bad Thing according to Apple, and not everyone can afford (or write) a full ISAM (Indexed Sequential Access Method) utility.

Solution: Doodat #3, which includes some primitive (but useful) indexing routines. If used properly, they can be used for indexing files, arrays, or be used for look-up tables, etc.

All of the routines are based on the idea of a simple index, made up of 1-n index entries. Each index entry is a key value and it’s associated data value, and is defined in the index_entry structure below. The key and data values are always handled in pairs: for any given key, there is only one data value (provided it exists). Duplicate keys are not allowed, and both key and data values are limited to numeric values. What the key and data values actually represent depends on the application, an obvious example would be relating a part number to an offset into a file.

Several different indices can be manipulated using the same routines, it is the application’s responsibility to determine which index to use. If the indexes are small and/or few in number, they could be manually rebuilt each time the application is executed. Alternately, they could be saved between sessions, either as data files, or as resources: all that is needed the memory block referenced by the index handle (use GetHandleSize() to find it’s size). An elegant solution would be to save any or all data file indices as resources in the data file’s resource fork, but that would limit the index size to 32K.

Adding a new key to an index (or updating an existing key) is done by the db_insert_key() function: a pointer to the index handle, a key value, and the data value associated with the key are all passed as parameters. If the index handle is NIL, a new handle is allocated, otherwise, the index is expanded by one index entry, and the new key added to the index in ascending order. If the key value already exists in the index, the data value is updated with the new value.

Once an index has keys inserted into it, db_get_key() can be used to search the index for a given key value. The routine expects an index handle and a key value, then performs a binary search on the index. If the key value is found, the data value associated with the key is returned, otherwise -1 is returned to signal failure.

There may be times when it is necessary to find a key’s location in the index, thus db_get_seq_key() accepts an index handle and an entry number, then returns the key value found at that entry. Once again, -1 is returned to signal failure if the entry number is less than 1 or greater than the number of keys. This routine can be used to sequentially read through an index (in ascending order), using the following code:

/* 3 */

long  w_key, key_value;

w_key = 1L;
while (true)
 {
 key_value = db_get_seq_key(my_index, w_key++);
 if (key_value == -1L)
 break;

 my_data = db_get_key(my_index, key_value);
/*
** process my_data here
*/
 }

Some possible extensions to these routines include modifying them to store a character pointer as the key, providing non-numeric keys. For small indexes, the entire data record could be embedded as part of the index_entry structure, and a pointer to the structure returned by db_get_key().

The routines db_get_key(), db_get_seq_key(), and db_insert_key() all utilize the following definitions and structure:

/* 4 */

#define NIL 0L
/* Test a pointer for validity */
#define VALID_PTR(p) ((long)(p) &&
 ((long)(p) & 1L) == NIL)

/* Test a handle for validity */
#define VALID_HNDL(h)(VALID_PTR(h) &&
 VALID_PTR((long)(*(h)) & 0x00FFFFFF))

typedef struct
 {
 unsigned long   key;
 unsigned long   data;
 } index_entry;

/************************************************
**
** db_get_key()
**
** This routine performs a binary search on a
** list of index entries
**
** In:  index_hndl Handle to index
** target key value to find
**
** Out: -1 if NOT found, data value otherwise
**
*/

long
db_get_key(index_hndl, target)
Handle  index_hndl;
register long  target;
{
register index_entry *i_ptr;
register long    mid, low, high;

if (VALID_HNDL(index_hndl))
 {
 low = 1L;
 high = GetHandleSize(index_hndl) /
 sizeof(index_entry);

 while (low <= high)
 {
/* calculate the mid point of list */
 mid = ((low + high) >> 1) - 1;
 i_ptr = *index_hndl + (mid *
 sizeof(index_entry));

 if (i_ptr->key > target)
/* too big, so look in lower half  */
 high = mid;
 else if (i_ptr->key < target)
/* too small, so look in upper half */
 low = mid + 2;
 else
/* hmmm, guess we found it  */
 return(i_ptr->data);
 }
 }
return(-1L);
}/* end of db_get_key() */

/************************************************
**
** db_get_seq_key()
**
** This routine reads a list of index entries,
** returning a key based on a sequential number
**
** In:  index_hndl Handle to index
** key_numkey number to return
**
** Out: -1 if NOT found, key value otherwise
**
*/

long db_get_seq_key(index_hndl, key_num)
Handle  index_hndl;
short   key_num;
{
index_entry *i_ptr;
long    result = -1L;
short   num_keys;

if (VALID_HNDL(index_hndl)
 {
/* count number of keys in index */
 num_keys = GetHandleSize(index_hndl) /
 sizeof(index_entry);
 if (--key_num < num_keys)
 {
/* calculate offset into the index */
 i_ptr = *index_hndl + (key_num *
 sizeof(index_entry));
 result = i_ptr->key;
 }
 }

return(result);
}/* end of db_get_seq_key() */

/************************************************
**
** db_insert_key()
**
** This routine inserts a key into an index.
**
** In:  index_hndl Handle to index
** target key value to insert
** data data value associated
** with the key
**
** Out: N/A
*/

void
db_insert_key(index_hndl, target, data)
Handle  *index_hndl;
long    target;
long    data;
{
register index_entry *i_ptr, *n_ptr;
register long    mid, low, high, i_size;

/* empty list is special case! */
if (!VALID_HNDL(*index_hndl))
 {
/* allocate new handle */
 *index_hndl = NewHandle(sizeof(index_entry));
 ((index_entry *)(**index_hndl))->key = target;
 ((index_entry *)(**index_hndl))->data = data;
 }
else
 {
 low = 1L;
 high = i_size = GetHandleSize(*index_hndl) /
 sizeof(index_entry);

 while (low <= high)
 {
/* calculate the mid point of list */
 mid = ((low + high) >> 1) - 1;
 i_ptr = *index_hndl + (mid *
 sizeof(index_entry));

 if (i_ptr->key > target)
/* too big, so look in lower half */
 high = mid;
 else if (i_ptr->key < target)
/* too small, so look in upper half */
 low = mid + 2;
 else
/* found it, so store new key value */
 i_ptr->data = data;
 }

/* extend handle by size of one entry*/
 SetHandleSize(*index_hndl, (i_size + 1) *
 sizeof(index_entry));
/* test for memory error here */
 n_ptr = i_ptr = **index_hndl + (mid * 
 sizeof(index_entry));
 memcpy(++n_ptr, i_ptr, (i_size - mid) *
 sizeof(index_entry));
/* do we insert as right or left? */
 if (i_ptr->key < target)
 i_ptr = n_ptr;
/* and move in the new key and data value */
 i_ptr->key = target;
 i_ptr->data = data;
 }
}/* end of db_insert_key() */

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

FileZilla 3.51.0 - Fast and reliable FTP...
FileZilla (ported from Windows) is a fast and reliable FTP client and server with lots of useful features and an intuitive interface. Version 3.51.0: Bugfixes and minor changes: Fixed import of... Read more
KeyCue 9.8 - Displays all menu shortcut...
KeyCue has always been a handy tool for learning and remembering keyboard shortcuts. With a simple keystroke or click, KeyCue displays a table with all available keyboard shortcuts, system-wide... Read more
AppCleaner 3.5.1 - Uninstall your apps e...
AppCleaner allows you to uninstall your apps easily. It searches the files created by the applications and you can delete them quickly. Version 3.5.1: Fixed a code-signing issue causing AppCleaner... Read more
A Better Finder Attributes 7.03 - Change...
A Better Finder Attributes allows you to change JPEG & RAW shooting dates, JPEG EXIF meta-data tags, file creation & modification dates, file flags and deal with invisible files. Correct EXIF... Read more
Postbox 7.0.33 - Powerful and flexible e...
Postbox is a desktop feature-stuffed email client, news application, and feed reader that helps you manage your work life and increase productivity. Now you can organize all your email accounts in... Read more
Adobe InCopy 16.0 - Create streamlined e...
InCopy is available as part of Adobe Creative Cloud for $52.99/month (or $4.99/month for InCopy app only). Adobe InCopy, ideal for large team projects involving both written copy and design work,... Read more
Steam 2.0 - Multiplayer and communicatio...
Steam is a digital distribution, digital rights management, multiplayer and communications platform developed by Valve Corporation. It is used to distribute a large number of games and related media... Read more
Adobe Lightroom Classic 10.0 - Import, d...
You can download Lightroom for Mac as a part of Creative Cloud for only $9.99/month with Photoshop, included as part of the photography package. The latest version of Lightroom gives you all of the... Read more
Adobe InDesign 16.0 - Professional print...
InDesign is available as part of Adobe Creative Cloud for as little as $20.99/month (or $9.99/month if you're a previous InDesign customer). Adobe InDesign is part of Creative Cloud. That means you... Read more
Adobe After Effects 17.5 - Create profes...
After Effects is available as part of Adobe Creative Cloud for $52.99/month (or $20.99/month for a single app license). The new, more connected After Effects can make the impossible possible. Get... Read more

Latest Forum Discussions

See All

Genshin Impact Guide - Gacha Strategy: W...
If you're playing Genshin Impact without spending money, you'll always need to be looking for ways to optimize your play to maximize rewards without getting stuck in a position where you're tempted to spend. The most obvious trap here is the game'... | Read more »
Genshin Impact Adventurer's Guide
Hello and well met, fellow adventurers of Teyvat! Check out our all-in-one resource for all things Genshin Impact. We'll be sure to add more as we keep playing the game, so be sure to come back here to check for updates! [Read more] | Read more »
Genshin Impact Currency Guide - What...
Genshin Impact is great fun, but make no mistake: this is a gacha game. It is designed specifically to suck away time and money from you, and one of the ways the game does this is by offering a drip-feed of currencies you will feel compelled to... | Read more »
XCOM 2 Collection on iOS now available f...
The XCOM 2 Collection, which was recently announced to be coming to iOS in November, is now available to pre-order on the App Store. [Read more] | Read more »
Presidents Run has returned for the 2020...
IKIN's popular endless runner Presidents Run has returned to iOS and Android just in time for the 2020 election season. It will see players choosing their favourite candidate and guiding them on a literal run for presidency to gather as many votes... | Read more »
New update for Cookies Must Die adds new...
A new update for Rebel Twins’ platformer shooter Cookies Must Die is coming out this week. The update adds quite a bit to the game, including new levels and characters to play around with. [Read more] | Read more »
Genshin Impact Guide - How to Beat Pyro...
The end game of Genshin Impact largely revolves around spending resin to take on world bosses and clear domain challenges. These fights grant amazing rewards like rare artifacts and ascension materials for weapons and adventurers, but obviously... | Read more »
Moto Rider GO has received a huge update...
Moto Rider GO: Highway Traffic is a popular free-to-play racing game that initially launched back in 2017 and has since racked up over 100 million downloads. Today it has received a sizeable update that introduces several KTM and Husqvarna... | Read more »
ORDESA is a spooky interactive film that...
French studio Cinétévé Experience and ARTE have released interactive movie ORDESA for iOS and Android today. It arrives at the perfect time of year, telling a story about a mysterious haunted house that the viewer suddenly finds themselves lost in... | Read more »
Genshin Impact Guide - How to Beat Storm...
If you've followed our progression guide for Genshin Impact up to Adventure Rank 25, you have reached the point where you can face off against Stormterror on a weekly basis for some pretty sweet rewards. Beating this deadly dragon isn't as easy as... | Read more »

Price Scanner via MacPrices.net

AT&T offers the Apple iPhone 11 for $10/m...
AT&T is offering Apple’s 64GB iPhone 11 for $10 per month, for customers opening a new line of service, no trade-in required. Discount is applied via monthly bill credits over a 30 month period.... Read more
Apple’s 2020 11″ iPad Pros on sale today for...
Apple reseller Expercom has new 2020 11″ Apple iPad Pros on sale for $50-$75 off MSRP, with prices starting at $749. These are the same iPad Pros sold by Apple in their retail and online stores: – 11... Read more
Did Apple Drop The Ball By Not Branding Its C...
EDITORIAL: 10.21.20 – In the branding game, your marketing strategy can either be a hit or a miss and the latter is the case for Apple when it missed out on an opportunity to brand its “SE” series of... Read more
27″ 6-core and 8-core iMacs on sale for up to...
Adorama has Apple’s 2020 27″ 6-core and 8-core iMacs on sale today for $50-$100 off MSRP, with prices starting at $1749. Shipping is free: – 27″ 3.1GHz 6-core iMac: $1749, save $50 – 27″ 3.3GHz 6-... Read more
Apple’s 16″ MacBook Pros are on sale for $300...
B&H Photo has 16″ MacBook Pros on sale today for $300-$350 off Apple’s MSRP, starting at $2099. Expedited shipping is free to many addresses in the US. Their prices are among the lowest available... Read more
Apple has 2020 13″ MacBook Airs available sta...
Apple has a full line of Certified Refurbished 2020 13″ MacBook Airs available starting at only $849 and up to $200 off the cost of new Airs. Each MacBook features a new outer case, comes with a... Read more
These major wireless carriers will give you a...
Apple’s wireless partners are offering several deals on iPhone 12 pre-orders right now. If you’re willing to switch carriers, you can get a free iPhone 12 right now. Here’s where to take advantage of... Read more
4 day sale at Sams Club: Save $24-$29 on Appl...
Sams Club has Apple Watch Series 6 GPS models on sale this week for $24-$29 off Apple’s MSRP, starting at $374. Sale ends this Thursday, October 22nd: – 40mm Apple Watch Series 6 GPS: $374.98, save $... Read more
US Cellular offers Apple iPhone 12 Pro for $8...
US Cellular has the 2020 128GB iPhone 12 Pro available for $829 off MSRP for new customers signing up for an Unlimited data plan, or $5.66 per month. Cost of the phone is spread over a 30 month... Read more
Buy one Apple Watch SE or Series 6 at AT&...
Buy one Apple Watch SE or Series 6 at AT&T, and get $200 off the price of a second Apple Watch. One new line required, and price discounted reflected in bill credits over a 30 month period. The... Read more

Jobs Board

*Apple* Endpoint Engineer - Argonne National...
Apple Endpoint Engineer **Requisition Number:** **408932** **Location:** **Lemont, IL** **Functional Area:** **Information Technology** **Division:** **BIS\-Business Read more
Core *Apple* Computing Pro - Best Buy (Unit...
**786358BR** **Job Title:** Core Apple Computing Pro **Job Category:** Store Associates **Store Number or Department:** 001080-Lake Charles-Store **Job Read more
Department Manager- Tech Shop/ *Apple* Stor...
…their parents want, and our faculty needs. As a Department Manager in our Tech Shop/ Apple Store you will spend the majority of your time on the sales floor engaging Read more
Geek Squad *Apple* Consultation Professiona...
**782284BR** **Job Title:** Geek Squad Apple Consultation Professional **Job Category:** Store Associates **Store Number or Department:** 000140-San Carlos-Store Read more
*Apple* /Mac IT Support - Randstad (United St...
Apple /Mac IT Support **job details:** + location:San Francisco, CA + salary:$45 - $50 per hour + date posted:Thursday, October 8, 2020 + job type:Contract + Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.