Quote:
qApp->connect(header, &QHeaderView::sectionClicked, header, &ListIconHeaderClicked)
This is incorrect syntax for a connect() statement. The first half is OK - you are saying you want to connect to an instance of the QHeaderView class ("header") and its sectionClicked() signal. The second half is wrong for two reasons: first, if you want to handle that signal in some other class that you have implemented, then you put the instance pointer for that class as the third argument (not "header"); and second, the next argument must be the address of a method for the class you used as the third argument: