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### 12. Finding Errors

### 12.1 Debugging Macros provided by Qt

The Debugging Macros provided by the Qt library can be read on the debug.html page of your Qt Online Reference Documentation, acessable on the link "Debugging Techniques" at the Qt Documentation index page.

The most recently used macros are

- ASSERT(b)
- CHECK_PTR(p)

Thereby, b is a boolean expression. Gives out a debugging warning if b is false; p is a pointer which is checked and gives out a warning, if p is null.

Details can be found in the Qt Online Reference.

### 12.2 KDE Macros

NOTE: This chapter is a copy of Kalle Dalheimer's kalle@kde.org explanation document about the KDEBUG macros included with the KDE libs package as kdebug.html

Last modified: Sat Sep 13 11:56:01 CEST 1997

What is KDebug

KDebug is a system of macros and functions that makes using diagnostic messages in your code more efficient. You can give a message one out of four severity level and an area. You can choose at runtime where diagnostic messages should go and which of them should be printed at all. How to use KDebug in your code

The macro KDEBUG

Using KDebug is very simple. All you have to do is to #include <kdebug.h> at the beginning of every source file in which you want to use diagnostic messages and output the messages by calling the macro KDEBUG. This macro expects three parameters. The first is the severity level. Use one of the following constants:

- KDEBUG_INFO
- KDEBUG_WARN
- KDEBUG_ERROR
- KDEBUG_FATAL

The second parameter is the area. An area is a part of KDE that you define yourself. You can then at runtime choose from which areas diagnostic messages should be printed. Please see the file kdelibs/kdecore/kdebugareas.txt for a list of already allocated area ranges. Choose an area within the range allocated for your application. If your application is not yet in here and you have CVS access, you can allocate a range for your application here, otherwise just mail me. It is probably a good idea to define symbolic constants for the areas you want to use, but this is completely up to you. The third parameter, finally, is the text you want to output. KDebug automatically prepends the logical application name if you output to a file, to stderr or to syslog. A newline is always appended, you need not (and should not) use one yourself. If you need parameters, you can use one of the macros KDEBUG1, ..., KDEBUG9. These allow for one to nine additional arguments. The syntax is exactly the same as with printf, i.e. you have to include format specifiers in your message which get replaced by the additional parameters. An example:

> `

>     KDEBUG3( <idx/KDEBUG_INFO/, kmail_composer, "Message no. %d to %s has %d bytes",
>               message_no, aMessage.to(), aMessage.length() );

> `

KASSERT

There are also the macros KASSERT, KASSERT1, ..., KASSERT9 which work just like their KDEBUG-counterparts, except that they have an additional bool as their first parameter. Only if this evaluates to false will the message be output. Note: You should not use neither KDEBUG nor KASSERT before the KApplication object is constructed. Note 2: KDebug provides no means for internationalization because it is meant strictly for developers only. If you want to inform the user about an erroneous condition (like "this file is not writable"), use KMsgBox.

Compiler switches

You do not need any special compiler switches in order to use KDebug. But when you ship your product (this mainly applies to people who create distributions like .rpm or .deb packages), you should compile with the switch -DNDEBUG. This will simply remove all the debugging code from your application and make it smaller and faster (e.g. it uses 256K less non-shareable memory).

How to manage diagnostic messages at runtime

You can press Ctrl-Shift-F12 in every KApplication at any time, and the "Debug Settings"-Dialog will appear. Here you can define separately for every severity level what should be done with the diagnostic messages of that level. The following settings are available:

- Output: In this Combobox, you can choose where the messages should be output. The choices are: "File", "Message Box", "Shell" (meaning stderr) and "syslog". Please do not direct fatal messages to syslog unless you are the system administrator yourself. The default is "Message Box".
- File: This is only meaningful when you have chosen "File" as the output and provides the name of that file (which is interpreted relatively to the current directory). The default is kdebug.dbg.
- Area: The areas which should only be output. Every message that is not mentioned here will simply not be output (unless this field remains empty which is the default and means that all messages should be output). Your can enter several areas separated by commas here, and you can also use area ranges with the syntax start-end. Thus a valid entry could be: 117,214-289,356-359,221. Please do not use whitespace.

Apart from this, you can also tick the checkbox "Abort on fatal errors". In this case, if a diagnostic message with the severity level "KDEBUG_FATAL" is output, the application aborts with a SIGABRT after outputting the message. When you close the dialog with OK, your entries apply immediately and saved in your application's configuration file. Please note that these settings are specific for one singular application! When you press cancel, your entries are discarded and the old ones are restored.

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