What is the solution of this error?

mit_cruze

I get this error ONLY when I use SDL Libraries.

(.qtversion[qt_version_tag]+0x0):-1: error: undefined reference to `qt_version_tag'

hskoglund

Hi, that 'qt_version_tag' is Qt checking that it loads the correct .so files (for example the libQt5Core.so.5 that belongs to 5.7). So if you get a message about "undefined reference to qt_version_tag" that means Qt is trying to load an old/wrong dll.

mit_cruze

Is there any solution If you know, please help me out!
I am running Qt 5.7 on ubunutu

hskoglund

Hi, check that you've #included "qglobal.h" in all .cpp files. (That's where the qt_version_tag is defined.)

mit_cruze

THanks but still no luck!

hskoglund

Hmm, how's the output from ldd your-app? Perhaps there's some 5.5.1 libraries in there (because Ubuntu 16.04 comes with Qt 5.5.1 pre-installed).

kshegunov

@hskoglund said in What is the solution of this error?:

Hi, check that you've #included "qglobal.h" in all .cpp files. (That's where the qt_version_tag is defined.)

Henry, you've mentioned this before, so I went on and checked. It doesn't matter whether you include <QtGlobal> as the versioning tag is generated only when Qt's compiled (which I suspected, hence the double-check ;)). See here (notice the ifdef) and here (note the extern const char * that's built with the macro). However I do believe you were right the first time and the error is popping up because of binaries that are incompatible (it was when I encountered it).

@mit_cruze said in What is the solution of this error?:

THanks but still no luck!

As @hskoglund says, make sure you're not mixing up Qt builds.

hskoglund

@kshegunov Yes, you're right, I wasn't checking when/where the versioning tag is defined. Slightly confused, that error above: ... undefined reference to `qt_version_tag' is a linking error, right? But the similar error you got before, wasn't that when you tried to start you app?

kshegunov

@hskoglund said in What is the solution of this error?:

Slightly confused, that error above: ... undefined reference to `qt_version_tag' is a linking error, right? But the similar error you got before, wasn't that when you tried to start you app?

Yes I got it on loading, because I had unintentionally substituted the binaries my application is linked to.

As for your first question:
There's little distinction on Linux as the symbol resolution will be actually done at run-time (in contrast to Windows); and that's one big mother of a pitfall. :)