Dec 93 Tips, Tidbits
Volume Number: 9
Issue Number: 12
Column Tag: Tips & Tidbits
Tips & Tidbits 
By Neil Ticktin, Editor-in-Chief
This column is your opportunity to spread the word about little bits of
information that you find out about. These tidbits can be programming related or they
can be user tips that are particularly useful to programmers.
MacTech Magazine will pay $25 for every tip used, and $50 for the Tip of the
Month. Or you can take your award in orders or subscriptions.
To submit a tip, send in a letter to the magazine. E-mail is our preferred
method, but feel free to send something via the US Mail. See page two for all addresses.
If you do send snail mail, enclose a printed copy and a disk copy of the letter so that it
does not have to be retyped.
Tip of the Month: Accelerating MPW's Startup SequenceThis trick is described in the Examples folder that comes with MPW. But in
talking to other users, I was surprised to find few people know about it, and even fewer
use it.
When MPW is launched, it executes a script named “Startup,” which sets up
environment variables, aliases, custom menus, and so forth. This can take from
several seconds to over a minute.
It is easy to optimize this startup sequence. After launching MPW normally, copy
the following lines into the MPW Worksheet window. Then highlight them as a block
and press Enter:
/* 1 */
Rename "{MPW}"Startup "{MPW}"Startup.Old
Begin
Set
Export
AddMenu
End > "{MPW}"Startup
This creates an optimized Startup script that will typically execute two to ten
times faster than the original. The initial “Rename” command saves the original
Startup script, so you can revert to it if you decide you don’t like the results. But if
you do “before and after” timings, I think you’ll be happy with the speed
improvement.
There are a couple of caveats though. First, the optimized Startup script is not
organized and commented the same way the original is. If you frequently change your
MPW configuration, you might find the optimized script harder to read and edit. Or you
might find it to be easier; the point is that it is different.
Second, if you have UserStartup files that are often modified (such as
UserStartup•RunMenu, described in MacTech Magazine, October, 1993), you may
wish to add a line to the end of the optimized Startup script to forcibly execute the
UserStartup commands. With UserStartup•RunMenu as an example, here’s what the
command would look like:
Execute "{PrefsFolder}"UserStartup•RunMenu
In doing this, you will cause some startup commands to be executed more than
once (since some commands from the UserStartup will appear in the optimized Startup
script as well). As a final “tweak,” you should then edit the optimized Startup script
to delete any commands which will be carried out by forcibly executed UserStartup
scripts.
- Lee David Rimar, Absoft Corporation
Strings that go both ways
When writing programs in C on the Macintosh, one thing that we need to deal with
is the two possible formats of strings: C-style and Pascal-style. To save the repeated
conversion time between the two formats, I sometimes use a format I call the
two-in-one format that has both at once.
The C-style string uses a terminating zero character (null) at the end of the
string to mark it’s length. The Pascal-style string uses a length byte as the first byte
of the string (see figure). Both are allocated by allocating the space for the maximum
number of characters the string will hold plus one for either the length byte or the
termination byte. My two-in-one format uses both a length byte as it’s first byte and
the zero byte as it’s last. To allocate this, take the data size and add two for both the
Pascal-style length byte and the C-style terminator. The illustration shows how the
length byte, string data, and terminator are laid out.
To use this as a Pascal string, simply use it normally. To use it as a C string,
pass the string address as string + 1. Of course, if the size of the string is changed,
then either the length byte or the terminator will need to adjusted. If you use calls
that treat it as a C string, then the length byte will need adjusting. If you use
Pascal-style calls, the terminator will need adjusting. The adjusting isn’t always as
hard as you might think.
The following code fragment illustrates using the two-in-one string format:
/* 2 */
Str255 stringOne;
char stringTwo[50];
...
/* #1 Toolbox call uses Pascal-style string. */
GetIText ( dialogItemHandle, stringOne);
stringOne[stringOne[0] + 1] = ’\0’; // Add term. byte
...
/* #2 Uses C-style string and returns the num. of characters. */
stringTwo[0] = sprintf (stringTwo + 1, “foobar”);
...
/* #3 Two-in-one style, notice the length plus two. */
BlockMove (stringOne, stringTwo, stringOne[0] + 2);
In #1, the toolbox call returns a Pascal-style string, so, for the two-in-one
format we’ve got to add the terminator. We know that stringOne[0] is the length byte
and we know that stringOne[length] is the last byte of data in the string. So, the length
plus one is the terminator byte.
In #2, we’re using the string as a C-style string. Notice that the C-style string
starts at an offset of one, this avoids the Pascal-style length byte. Fortunately, sprintf
returns the number of bytes (characters) written if there’s no error so we can use it
to adjust the length byte. Other C library calls like printf, scanf and their derivatives
also return the number of characters processed.
In #3, we’re using the Toolbox call BlockMove() to copy a two-in-one format
string. Since the length is the length of the data, we’ve got to add two to allow for the
length byte and the terminator byte.
I’ve found that judicious use of this string format can save a lot of conversion in
string-heavy programs.
- Malcolm Teas
Step-step
In Think Pascal, the option key allows you to “step-step” through the code. Hold
down the option key and pull down the RUN menu. You will see the step-step option.
Step-step walks through your source code one line at a time, stepping into functions
and procedures. It’s like a guided tour through your own program. Hold down the
option key and browse through the Think Pascal menus. You may be surprised how
much the option key modifies in the menus.
- Lillian Thompson, Reno, Nevada