Subclass from Qt Ui Form Class, invalid use of incomplete type

[HappyCoder]

The includes are all Ok, to make it clear:

The base class is a Qt Form Class located in subdir ui/
ui/ui_calib_base.h
ui/ui_calib_base.cpp
ui/ui_calib_base.ui

This is the derived class from the base class
calib_analog.h
calib_analog.cpp

In my calib_analog i have no access to the ui pointer of the base class although i moved it into the protected section in "ui/ui_calib_base.h".

[d_stranz]

In my calib_analog i have no access to the ui pointer of the base class although i moved it into the protected section in "ui/ui_calib_base.h".

You -do- have access to it. As I said, this code:

namespace Ui {
class ui_calib_base;
}

namespace Ui {
class ui_calib_base;
}

To copy to clipboard, switch view to plain text mode 

only declares a forward reference to the Ui:: ui_calib_base class; it does not define the class. You need to include that actual header file that defines the Ui:: class. This file is created by MOC when it processes your .ui file.

The compiler is telling you that you are trying to use methods and variables of the Ui:: class in a place where all it knows is the name of the class (via the forward declaration) because it hasn't seen the actual definition. That's an "invalid use of an incomplete type".