|Please ask about problems and questions regarding this tutorial on answers.ros.org. Don't forget to include in your question the link to this page, the versions of your OS & ROS, and also add appropriate tags.|
Mixing Qt and Boost SignalsDescription: Avoiding the keyword issues created by qt's signal/slot macros.
Keywords: qt boost signals
Tutorial Level: BEGINNER
Qt uses preprocessor macros (fugly) for signals and slots. These conflict with boost's signals and slots class names. End result, is you can't compile when trying to use both in the same library/program.
Using Qt With 3rd Party Signals and Slots - qt dev documentation.
Qt4.1 introduced proper macro namespacing to qt signals and slots to avoid this situation (prefixes with Q_ and converts to uppercase - see below).
Application to Qt Ros
The tf package will raise this issue as soon as you include a tf header, so since tf is a rather core dependency, qt-ros on fuerte will use these definitions by default. The macro changes you will need to apply in your code are as follows:
signals -> Q_SIGNALS
slots -> Q_SLOTS
emit -> Q_EMIT
foreach -> Q_FOREACH
Electric wasn't updated for this api. To convert to the new keywords, create your new package, e.g.
> rosrun qt_create roscreate-qt-pkg my_package_foo
Suppose you now include the header file tf/message_filter.h to qnode.hpp in one of your sources and also add tf to the manifest.xml:
<depend package="tf" />
Compilation will fail, complaining about signals and slots.
To fix, add a new line in your CmakeList.txt:
rosbuild_prepare_qt4(QtCore QtGui) ADD_DEFINITIONS(-DQT_NO_KEYWORDS)
Now we change the Qt macros to upper case version. In our example we need to
main_window.hpp : change slots -> Q_SLOTS.
qnode.hpp : change signals -> Q_SIGNALS.
qnode.cpp : change emit to Q_EMIT.
Now everything should compile - be happy!
Thanks to Heber Sobreira for the preceding information.