qDebug() and qInfo() error code will never be executed

[tomy]

Hello to all,

In a C++ code on Qt Creator 4.8.1, I get the error/warning "code will never be executed" for the statement qDebug() << "curFile is "; in a method, although I have included <QDebug>!

Why please?

(I used it with the same format as this and it worked before, but I don't know why it's not possible now!)

[aha_1980]

@tomy are you on a release build?

I think this is a false positive then. There should already be a bugreport for that.

Edit: found it: QTCREATORBUG-20963

[SGaist]

Hi,

Do you have any condition before that line ? If so, are you sure it allows to go through that line ?

[Maaz Momin]

There is high possibility that a return statement is before that line which will be executed every time.

[J.Hilk]

@tomy
do you have by any change this

DEFINES += QT_NO_DEBUG_OUTPUT

in your pro file ?

[tomy]

@aha_1980
I face it while using the debug mode!
Either it's an error or simply a warning, it prohibits the code (that line) from executing.

@SGaist
Hi, Yes, it's inside an if-condition, but it oughtn't to be an issue. That output must be printed when the condition is accepted and not otherwise. So, there shouldn't actually be a warning/error, I suppose.

@Maaz-Momin, you hit the nail on the head!
Exactly. And it was the source of the issue indeed. Because when a function is going to be returned, there mustn't be any other code left. I hadn't noted that accurately enough, unfortunately.
Solved, thanks. Now both qInfo(), and qDebug() works (I mean before return)
But one side question, which is more common between these two for sending out messages, please?

@J-Hilk
No, I have't got that.

[tomy]

Another side question:
When we declare some functions under the private slots access modifier, they can be used "only" inside signal-slot connections, and we "cannot" use them as ordinary C++ functions. On the other hand, those functions defined under private/public can't be used for signal-slot connections either, but they can be used like any ordinary C++ function. Are these right please?

[J.Hilk]

@tomy
nope,
the best thing about signals and slots is, that you can call any signal and any slot like it is a normal function - because it actually is a normal function.

The only restriction is the private and public modifier.

[tomy]

@J.Hilk
Thanks.
But can functions defined under private/public modifier be used for signals too?

[J.Hilk]

@tomy said in qDebug() and qInfo() error code will never be executed:

@J.Hilk
Thanks.
But can functions defined under private/public be used for signals too?

actually no, a signal may not have a function body defined, IIRC.

[tomy]

@J.Hilk Thanks.
I meant just slots.

To sum up, can we say that all slots whether defined under private slots modifier or ordinary private/public modifiers can be used with or without a connection macro, but only those slots that are defined under private/public slots can be used by the connection macros?

I mean, the keyword slots in the header file must have a role. Mustn't it?

[SGaist]

Did you already read the dedicated chapter in Qt's documentation ?

[J.Hilk]

@tomy
I would recommend reading through @SGaist link, it's essential ;-)

To answer your question,

in c++ something like slots and signals or really any additional keywords are strictly prohibited inside the class header.

Therefore slots and signals are actually just void keywords for the regular compiler. However they are needed for the meta object compiler to search for function names and arguments to do the connect magic.

However this is also only true if you use the old Qt4 Syntax, with the new Qt5 one the receiving function can quite literally be anything.

• normal functions
• other signals (signal-signal is also possible with qt4 synt)
• slots
• lambdas
  ...