Qt Wt Signals conflict - an ugly workaround
Added by George McFie 10 days ago
For anyone interested …
I found an ugly workaround for the Qt / Wt Signal conflict issue. The underlying problem is that Qt defines ‘emit’ as a C/C++ macro so that it ‘looks like’ a keyword. But the Wt::WSignal class has a method called ‘emit’, and so whenever a #include occurs after some (not all) Qt headers, there is a potential for a compilation error.
My ugly workaround is to simply use ‘#undef emit’ prior to the #include that leads to the error. For example …
#undef emit
#include "WebServer.h"
… where WebServer is one of my classes – one that includes Wt headers – and ultimately Wt/Wsignal.h.
Unfortunately it’s not a ‘permanent’ fix, but rather one that needs to be applied as and when the issue arises.
If anyone has a better solution I would welcome your feedback.
Replies (3)
RE: Qt Wt Signals conflict - an ugly workaround - Added by Marcelo Antunes 9 days ago
And if on qt signals, you use Q_EMIT instead of emit?
RE: Qt Wt Signals conflict - an ugly workaround - Added by George McFie 8 days ago
I don't believe that that will help because the issue is not related to what we use (Q_EMIT or emit).
Rather it is due to the fact that a #define for 'emit' is defined somewhere in some Qt header - and that causes the conflict with the Wt::WSignal 'emit' method.
So if the Qt headers are included anywhere before the Wt headers are included, a compilation error will occur - regardless of how you write your own code.
In my own code I'm not even using the Qt signal/slot mechanism, but I do include some Qt headers for other functionality. This is enough to cause the problem - unless I use the #undef emit that I described above.
RE: Qt Wt Signals conflict - an ugly workaround - Added by Matthias Van Ceulebroeck 5 days ago
It's a pity that Qt defines this as such, not using the "convention" of prepending the project/library name to the definition.
Sadly not something we have much control over.
The offender seems to be:
#ifndef QT_NO_META_MACROS
# if defined(QT_NO_KEYWORDS)
# define QT_NO_EMIT
# else
# ...
# define Q_EMIT
#ifndef QT_NO_EMIT
# define emit
#endif
So either having QT_NO_META_MACROS or QT_NO_KEYWORDS should ensure you do not have the conflict.