Qt Widget App and libusb
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Hello, I am very new to QT and i managed to run a QT Helloworld! GUI app.
I also was able to compile LIBUSB library and run a function, INSIDE the qt widget app.
The problem is that the function will run and print to the console of Qt Creator only after I close(QUIT) the GUI window.So i was wondering how can i do to print the "printf" lines that my function executes into a Qlabel or Qtextfield in the GUI.
I found a post talking about using QThreads where the threas report the printable lines from printf's to the Qlabel or Qtextfield, or a variable.
I just need to get pointed towards the right way to do it, if someone can help me i really apreciate it!Thank you
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Hi
You can also just use
qDebug() << "hello";if you really must use printf , you can
use redirection to file and then load the file using a timer, into a QT widget.freopen("desiredFileName", "w", stdout);
But that said, printf in GUI programs is not super.
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Hi
You can also just use
qDebug() << "hello";if you really must use printf , you can
use redirection to file and then load the file using a timer, into a QT widget.freopen("desiredFileName", "w", stdout);
But that said, printf in GUI programs is not super.
@mrjj said in Qt Widget App and libusb:
Hi
You can also just use
qDebug() << "hello";if you really must use printf , you can
use redirection to file and then load the file using a timer, into a QT widget.freopen("desiredFileName", "w", stdout);
But that said, printf in GUI programs is not super.
Im using print f because i need to present the data from the USB devices in a HEX format and of course i dont know how to do it in qt. its been a weeks since i installed the Qt creator and im starting to learn.
If there is another way im open to try it -
Hi
The QString can convert to/from hex. And so can ByteArray
The simple form is
QString hex = QString::number( nValue, 16 );
and for more controluint decimal = 203888026;
QString hexvalue = QString("0x%1").arg(decimal, 8, 16, QLatin1Char( '0' ));For byte array , please see
http://doc.qt.io/qt-5/qbytearray.html#toHex -
OK ive fixed my problem by doing this:
qDebug() << "Vendor = " << hex << desc.idVendor << "|" << hex << desc.idProduct;BUT, this is printed when i click the button (WHICH is what i want) .
NOW, my issue is that, when i EXIT the app i get a second Print, like the function executes once more, why is that? -
OK ive fixed my problem by doing this:
qDebug() << "Vendor = " << hex << desc.idVendor << "|" << hex << desc.idProduct;BUT, this is printed when i click the button (WHICH is what i want) .
NOW, my issue is that, when i EXIT the app i get a second Print, like the function executes once more, why is that?@AleFachini
well I would place a break point and see if its really the case.
It could also be you still have a printf left and its buffered, so you need to call
fflush(stdout);
to see it.
Or add a newline to printf -
Of Course i did not remove the printf!! now i only get the print wehen i click and not the buffered print!!!
My last question and ill mark this as SOLVED, why is that the printf appear when i CLOSE the app? it has smething to do with the thread being used for the GUI? or why?
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Of Course i did not remove the printf!! now i only get the print wehen i click and not the buffered print!!!
My last question and ill mark this as SOLVED, why is that the printf appear when i CLOSE the app? it has smething to do with the thread being used for the GUI? or why?
@AleFachini
Hi
As the link talks about its about
"printf" being buffered. (inside GUI)
So u must call
fflush(stdout); ( after printf)
or have newline in the printf. -
OK, This is SOLVED then, but i dont find the option to mark it, Thanks!
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OK, This is SOLVED then, but i dont find the option to mark it, Thanks!
@AleFachini
Hi
Inside the Topic Tool button on the first post.
If not there, u need to convert it to question first:)
