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Debugging Qtopia Applications

• Introduction
• Using gdb
• Build the Application with Debug Symbols
• Run the Debugging Environment
• Debug Crashes
• qlog - Categorized Logging
• References

Introduction

Qtopia provides GNU Debugger gdb to monitor program execution and to examine program status in the event of a crash and the qlog function to provide categorized logging of debug information. The following sections describe how to used gdb in a Linux environment and how to call implement the qlog function.

Using gdb

This section provides instructions on how to debug Qtopia applications using igdb in a Linux environment.

Build the Application with Debug Symbols

To build an application with debug symbols:

• pass -debug to configure or add debug to the .pro file CONFIG settings as follows:

      CONFIG += debug

• build the application and install the application binary into the /opt/Qtopia/bin directory using the following commands:

      $ make clean
      $ make
      $ make install

Run the Debugging Environment

To run the debugging environmnent:

• start the virtual framebuffer environment
• start the Qtopia environment
• start gdb

using the following commands:

    $ qvfb &
    $ qpe &
    $ gdb theProgram
    (gdb) r # run

Alternatively to debug an application outside of the Qtopia environment:

• start the virtual framebuffer environment
• ensure the application hooks into the virtual frame buffer

using the following commands:

    $ qvfb &
    $ gdb theProgram
    (gdb) set args - qws # we need this to hook to the virtual frame buffer.
    (gdb) list # if you want to list the main.cpp file
    (gdb) b 6 # break at line six
    (gdb) r # run
    (gdb) s # step into
    (gdb) r # continue

Debug Crashes

If an application built with debug crashes, a core file is produced. Use the following commands to examine the core file contents:

    $ gdb theapplication core
    (gdb) backtrace full

qlog - Categorized Logging

Qtopia provides the qlog(CategoryIdentifier) function for categorized logging.

The syntax for logging is:

         qLog(I18n) << "Language loaded:" << lang;

The categories are declared by use of one of these macros:

• QLOG_DISABLE(CategoryIdentifier) - no logging code is generated.
• QLOG_ENABLE(CategoryIdentifier) - logging code is always generated and invoked.
• QLOG_OPTION(CategoryIdentifier,expr) - logging code is always generated, invoked if expr is true at the time the log is issued, expr may be cached.
• QLOG_OPTION_VOLATILE(CategoryIdentifier,expr) - as above, but expr is not cached.
• QLOG_DISABLE_UNCATEGORIZED - no logging code is generated for the empty category (qLog() << values).

The CategoryIdentifier has _QLog appended within the macros, so it can be any identifier you choose. The associated type name might be a useful choice:

         qLog(QWidget) << "Created" << name;

Example mechanisms by which your expr might choose whether logging is enabled include:

• Look up the CategoryIdentifier as a key in QSettings.
• Return a field from a global record that is set at startup.

References

• Qt Debugging Techniques
• gdb: The GNU Project Debugger - (http://www.gnu.org/software/gdb/gdb.html)
• gdb Reference Card - (http://www.refcards.com)