Qt MACro Keywords Cause Name Collisions

Qt macro keywords cause name collisions

You can define the QT_NO_KEYWORDS macro, that disables the “signals” and “slots” macros.

If you use QMake:

 CONFIG += no_keywords

(Qt Documentation here)

If you’re using another build system, do whatever it needs to pass -DQT_NO_KEYWORDS to the compiler.

Defining QT_NO_KEYWORDS will require you to change occurrences of signals to Q_SIGNALS and slots to Q_SLOTS in your Qt code.

If you cannot change all the Qt code, e.g. because you're using third-party libraries not being "keyword-clean", you could try to undefine "signals" locally before including cdk.h:

#undef signals
#include <cdk.h>

I'd recommend to use no_keywords though if possible, as it is less tedious and error-prone.

C++, Qt: Variable named slots in included external library

Adding QT_NO_KEYWORDS (-DQT_NO_KEYWORDS) definition to your build will prevent Qt from defining foreach, signals, slots which may collide with other frameworks.

Related answer:

• CDK Collides With Qt "signals"

Related doc:

• http://doc.qt.io/qt-5/signalsandslots.html#using-qt-with-3rd-party-signals-and-slots

Using library which has a function name already defined in another used library

The solution that worked for me is to reorder the order of my included files.

I put the #include <opencv2/face.hpp> before any call to any Qt include file. so that the emit keyword will not be defined yet.

And Recursively, if your header containing #include <opencv2/face.hpp> is included in another header file in your project, be careful to put it before any Qt include file, and the same for the second file.

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The important is to make sure to call #include <opencv2/face.hpp> before any call to to the definition of the Qt macro emit. You will be sure that your code will be compiled without any collision.

Using emit vs calling a signal as if it's a regular function in Qt

emit is just syntactic sugar. If you look at the pre-processed output of function that emits a signal, you'll see emit is just gone.

The "magic" happens in the generated code for the signal emitting function, which you can look at by inspecting the C++ code generated by moc.

For example a foo signal with no parameters generates this member function:

void W::foo()
{
    QMetaObject::activate(this, &staticMetaObject, 0, 0);
}

And the code emit foo(); is pre-processed to simply foo();

emit is defined in Qt/qobjectdefs.h (in the open-source flavor of the source anyway), like this:

#ifndef QT_NO_EMIT
# define emit
#endif

(The define guard is to allow you to use Qt with other frameworks that have colliding names via the no_keywords QMake config option.)

boost::Q_FOREACH' has not been declared

This could be caused by the conflict between boost and Qt. See this post

Someone suggested using CONFIG += no_keywords in your project file.

But I've also seen a ticket to fix this issue closed.. https://svn.boost.org/trac/boost/ticket/6455
So not sure whether this could help your problem

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