QByteArray losing first element Qt 6.8

[mishaalnaeemdev]

I am facing a weird issue.

I am using QMetaMethod to get signal signature. Debugging the signal Signature gives the correct value. However, on connect it loses the first letter.

QMetaMethod signal = metaProperty.notifySignal();

QByteArray signalName = signal.name();
 QByteArray signalSignature = signal.methodSignature();

qDebug() << "Signal name:" << signalName; qDebug() << "Signal signature:" << signalSignature;

connect(obj, signalSignature, this, SLOT(onPropertyChanged()));

This is the output.

Signal name: "valueChanged" 
Signal signature: "valueChanged(int)" 
valueChanged(int) 
qt.core.qobject.connect: QObject::connect: No such signal cTestDataPoint::alueChanged(int) 
qt.core.qobject.connect: QObject::connect:  (sender name:   'TestDataPoint_1')

I have also tried using

const char* signalStr = signalSignature.constData();

and passing the signalStr instead. However, it has the same result. The conversion to char* printed gives correct name too, but on connect it loses first char.

Any ideas?

[Christian Ehrlicher]

@mishaalnaeemdev said in QByteArray losing first element Qt 6.8:

Any ideas?

You don't use SIGNAL() macro so you just pass the plain signature to QObject::connect() which is wrong. SIGNAL() and SLOT() are there for a reason...

https://code.qt.io/cgit/qt/qtbase.git/tree/src/corelib/kernel/qobjectdefs.h#n52

[mishaalnaeemdev]

I have tried that,

connect(obj, SIGNAL(signalSignature), this, SLOT(onPropertyChanged()));

but I end up getting

qt.core.qobject.connect: QObject::connect: Parentheses expected, signal cTestDataPoint::signalSignature

Although, that issue should have been with signal name, not signal signature. Both are giving the same issue

[Christian Ehrlicher]

Since it's a compile time macro which combines two constant char arrays it won't work with a non-constant (at compile time) QByteArray. Simply look at the macro what it is doing and do it in your code when you want to do such a strange connect by yourself.
What are you trying to achieve at all?

[SGaist]

Hi,

Beside the good question of @Christian-Ehrlicher about your use case, if you want to use meta objects, then do it all the way for both signals and slots. That will make your life easier.