How to get handle of ccombobox in mfc

The line of code you've presented isn't getting the handle to anything - it's apparently trying to recover the pointer to a CComboBox MFC wrapper object that's a child of the window that supplies the this pointer the code is executed under.

So...

IF you really want a pointer to the MFC wrapper object NEVER use reinterpret_cast, use static cast.

auto pComboBox = static_cast<ccombobox>( GetDlgItem( IDC_COMBO1 ) );</ccombobox>

IF you actually want the handle use the m_hWnd member of whatever is returned by GetDlgItem, e.g.

auto handle = GetDlgItem( IDC_COMBO1 )->m_Hwnd;

Try those lines of code and see what happens. If neither do what you want perhaps modify your question to reflect what you want to do!