Question

I’m building a GUI class for C++ and dealing a lot with pointers. An example call:

mainGui.activeWindow->activeWidget->init(); 

My problem here is that I want to cast the activeWidget pointer to another type. activeWidget is of type GUI_BASE. Derived from BASE I have other classes, such as GUI_BUTTON and GUI_TEXTBOX. I want to cast the activeWidget pointer from GUI_BASE to GUI_TEXTBOX. I assume it would look something like this:

(GUI_TEXTBOX*)(mainGui.activeWindow->activeWidget)->function(); 

This isn’t working, because the compiler still thinks the pointer is of type GUI_BASE. The following bit of code does work, however:

GUI_TEXTBOX *textbox_pointer; textbox_pointer = (GUI_TEXTBOX*)mainGui.activeWindow->activeWidget; textbox_pointer->function(); 

I’m hoping my problem here is just a syntax issue. Thanks for the help 🙂

Answer 1

The problem is that casts have lower precedence than the . -> () [] operators. You’ll have to use a C++ style cast or add extra parentheses:

((GUI_TEXTBOX*)mainGui.activeWindow->activeWidget)->function();  // Extra parentheses dynamic_cast<GUI_TEXTBOX*>(mainGui.activeWindow->activeWidget)->function();  // C++ style cast