Development/FAQs/Debugging FAQ/ja

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Dr Konqi が出ないようにするにはどうしたら良いですか?

KDE_DEBUG 環境変数を1に設定してください。

To get Dr Konqi back, unset the KDE_DEBUG environment variable.


  • To avoid Dr Konqi:
export KDE_DEBUG=1
  • To see Dr Konqi:

How do I switch Dr Konqi to developer mode?

Edit file $KDEHOME/share/config/drkonqirc and add the following:


core ファイルって何ですか? どうすれば core ファイルを得ることができますか?

core ファイルとはアプリケーションがクラッシュしたときのメモリイメージです。これを使うことによって、どの変数がセットされていたり、どこでアプリがクラッシュしたかを知ることができます。

いくつかのディストリビューションでは core ファイルの生成を不可にしています。生成できるようにするには ulimit -c unlimited を実行してください。

いったん core ファイルが手に入ったら、"gdb appname core" で調べることができます。これで gdb は与えられたアプリケーション用に core ファイル上でオープンできます。gdb のプロンプトが出たら、bt というコマンドが役に立ちます。これはクラッシュのバックトレースを生成することができます。gdb の使い方についてもっと情報がほしいなら、こちらのページを見て下さい。

What tools are available to debug my application?

  • kDebug() (kdDebug() in KDE3) calls are a simple but efficient way to debug an application.
  • gdb, the GNU debugger, is the quickest way to execute step-by-step and investigate variables (recommended versions are gdb >= 6.x)
  • Valgrind
  • kdbg is a nice graphical frontend to gdb with a KDE GUI. It has support for many Qt types (including QString).
  • Memory leak tracer : See kdesdk/kmtrace. The README explains it all.
  • qdbus and dbus-viewer from Qt allow to browse DBus interfaces and to easily make DBus calls.

Check this page and kdesdk, there are a bunch of useful scripts there.

How do I print a QString in gdb?

Check out kdesdk, and add this line to your ~/.gdbinit :

source /path/to/kde/sources/kdesdk/scripts/kde-devel-gdb

Then in gdb you can do printqstring myqstring to see its contents. For instance, QString myqstring = QString::fromLatin1("contents"); can be examined using

(gdb) printqstring myqstring
$1 = "content"

See the kde-devel-gdb file for the other macros it defines.

I have no symbol when I debug an app that uses kpart, what should I do?

You must stop just after the main to load the debugging symbols of the shared library. After that, you can debug normally. One can go as far as creating a gdb macro, to stop right after the part was loaded. For kword, by example, I use:

define startkword
break main
break 'KoDocument::KoDocument(int, QWidget *, char const *, 
                       QObject *, char const *, bool)' cont

How do I debug an ioslave?

See debugging ioslaves

Why isn't my signal and slot connection working?

Here are some steps that you can use to troubleshoot why your signal/slot connection is not working (your slot does not get called for some reason).

1) Verify that the connect() doesn't print a warning to the console at runtime.

If it does, check that you wrote Q_OBJECT, that the parameter names are not in the connect, that the parameter types are compatible, and that the slot is defined, and that the moc was compiled.

1b) Or you can just check to see what connect() returns as a bool. Although this won't give you the error message. 2) Verify that the signal is indeed emitted 3) Verify that the receiver isn't already deleted at that time 4) Verify that emitter->signalsBlocked() returns false

KDE 4 specific

デバッグ用の出力を標準エラー (stderr) に出したいのですが、おすすめの方法は何ですか?

kDebug() を使うとよいでしょう。

#include <kdebug.h>
kDebug() << "KMyApp just started";

文法は cout とほとんど同じで、多くのネイティブな型を "<<" の間に使えます。これはデバッグメッセージを出力しますが、リリース時に(--disable-debug で)自動的に無効にすることができます。もし、メッセージをリリース中も出力したいならば、それらは警告やエラーなので kWarning()kError() を使って下さい。

Components and libraries are advised to use a debug area number, as in kDebug(1234). For this, the number must be registered in kdelibs/kdecore/kdebug.areas. Debug areas make it possible to turn off or on the debug output for specific area numbers, using the kdebugdialog program, which is part of kdebase. kdebugdialog --fullmode also permits to control where to log debug output. It is usually not necessary to register area numbers for standalone applications, unless it's so complex that you want to divide the output into several areas.

It is possible to omit the debug area number when calling kDebug by adding the following code to your top-level CMakeLists.txt:


For more information, about this, see Allen Winter's blog post.

To make it clear: do NOT use qDebug(), this one does not get disabled at releases. Also avoid using assert() or kFatal() which lead to a crash when something goes wrong and that is not a nice experience for the user. Better detect the error, output a kWarning() or kError(), and recover if possible.

To get timestamps with your debug output, which are useful for debugging multi-threaded, networked and asynchronous operations, export KDE_DEBUG_TIMESTAMP=1 before running your app. Since KDE SC 4.5.

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