Location of Qt 5.4 source code

[SGaist]

Some people change their system PATH rather than just in Qt Creator, that's why I asked the double check of PATH.

IIRC both debug and release dlls are stored in the same folder so Qt will check them all hence the incompatibility error message.

[slesher]

The problem is solved.
I have changed the part of code of connection:
@QSqlDatabase db;
db.addDatabase("QOCI");@

instead of

@QSqlDatabase db = QSqlDatabase::addDatabase("QOCI");@

When I guessed to change back, everything was ok.

Thanks a lot to all!