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May 93 Tips, Tidbits
Volume Number:9
Issue Number:5
Column Tag:Tips & Tidbits

Related Info: Quickdraw Color Quickdraw

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

DebugFStr and DebugFsStr are C macros that enable developers to drop into a low-level debugger, such as MacsBug or TMON, and display the contents of variables in a formatted manner. One example would be to display a long in hex, decimal or octal notation. Better yet, several variables can be shown together on the same message line that is displayed by a debugger. These macros can be used by both Think C and MPW C. Here's how to use 'em (Think C users):

Add the DebugFStr or DebugFsStr macro to your code. To use either macro, include the ANSI (or ANSI-small) and the MacTraps libraries in your project. You must also include the "stdio.h" header file in any source file in which you intend to use these macros. Don't forget to define 'AND' because it is necessary for the syntax of both macros. Macro definitions:

/* 1 */
#define DebugFStr(x,y,z)  sprintf((char *)x,(char *)y,z);      
 c2pstr((char *)x);\
#define DebugFsStr(x,y) { Str255 a_temporary_string = "\0";    
 sprintf((char *)a_temporary_string,(char *)x,y);\
 c2pstr((char *)a_temporary_string); \
#define AND ,

Place DebugFStr or DebugFsStr calls throughout your code in places where you want to drop into your low-level debugger and view the contents of variables. The syntax for using each macro is:

/* 2 */

DebugFStr((char *)resultString,(const char *)formatString,var1 AND var2 
AND varN)
DebugFsStr((const char *)formatString,var1 AND var2 AND   varN)

When using DebugFStr, you must declare and pass a string variable that will be used by the macro to hold the resulting formatted string. This string is a Str255.

FormatString should be a C string constant, enclosed in double-quotes, and can contain formatting information that is identical to the formatting information used for ANSI C's sprintf function.

The variables var1 through varN must be separated by the word AND and the variables must be ordered to correspond directly to the order of the variables defined in the formatString. See the Think C Standard Libraries Reference guide for more information about the sprintf function.

NOTE: The combined length of the formatString and the formatted variables cannot exceed 255 characters, because both macros call DebugStr which requires a Pascal-style string.

NOTE: Notice in the syntax for both macros that neither is delimited by a semicolon.

The only real difference between DebugFStr and DebugFsStr is that the DebugFsStr macro creates a temporary string variable for the formatted string result and DebugFStr requires you to supply a string which will be used by the macro to store the formatted string result.

Following is a function that demonstrates the use of DebugFStr.

/* 3 */

static void MyFunc(short dummy)
 long    tempL1 = 1000;
 long    tempL2 = 20;
 Str255  result;

 DebugFStr((char *)result,"In HEX, tempL1 is %#lX and tempL2 is %#lX.",
 tempL1 AND tempL2)
 tempL1 += tempL2;
 DebugFStr((char *)result,"In decimal, tempL1 is %ld.",templL1) }

In the sample function shown above, MyFunc would drop into your debugger two times. On the first drop, your debugger would display the message: In Hex, tempL1 is 0X3E8 and tempL2 is 0X14. On the second drop, your debugger would display the message: In decimal, tempL1 is 1020.

- Jerry Panagrossi

Int'l Biotech via AppleLink

Adding Touch to MPW

If you work much with makefiles, you may sometimes want an easy way to touch a file's modification date. MPW doesn't include a touch command, but it's easy to add one. Type this command into the MPW Worksheet and press Enter:

 Alias Touch "Setfile -m . "

With this alias, you can touch the last modification date of files by entering commands like "touch filename" (updates just the one filename) or "touch .f" (all files in current folder with names ending in ".f").

After you've tried this and decided it's something you'd like as a permanent feature in MPW, copy the above Alias command to your UserStartup file. That way it will be executed each time you launch MPW.

- Lee D. Rimar

Rochester Hills, MI

Subtle QuickDraw Change

If you are writing code that bypasses QuickDraw and writes directly to the screen, and your code is running under 32-bit QuickDraw, only mask off the upper two bits of the screen’s rowbytes value. Previous to 32-bit QuickDraw, the maximum value for rowbytes was $1FFE (bits 13-15 reserved for flags), but with 32-bit QuickDraw, the maximum restriction has been raised to $3FFE (only bits 14 & 15 are reserved).

In most situations, an application that does its own blits to the screen would not encounter any problems masking off bit 13 BUT the time has arrived where bit 13 is being used. For example, a screen of 2048 32-bit pixels requires a rowbytes value of $2000. Applications that mask off bit 13 will produce a rowbytes value of zero, and will wind up drawing only to the top line of the screen.

By the way, if you did overlook this subtle change to the pixmap structure in Inside Mac IV (Chapter 17, page 5), don't feel left out, as I've found popular commercial applications making the same mistake as well.

- John C. Signa

SuperMac Technology


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