Tree Control Item Labels
You typically specify the text of an item's label when adding the item to the tree control (CTreeCtrl). The InsertItem member function can pass a TVITEM structure that defines the item's properties, including a string containing the text of the label. InsertItem has several overloads that can be called with various combinations of parameters.
A tree control allocates memory for storing each item; the text of the item labels takes up a significant portion of this memory. If your application maintains a copy of the strings in the tree control, you can decrease the memory requirements of the control by specifying the LPSTR_TEXTCALLBACK value in the pszText member of TV_ITEM or the lpszItem parameter instead of passing actual strings to the tree control. Using LPSTR_TEXTCALLBACK causes the tree control to retrieve the text of an item's label from the application whenever the item needs to be redrawn. To retrieve the text, the tree control sends a TVN_GETDISPINFO notification message, which includes the address of a NMTVDISPINFO structure. You must respond by setting the appropriate members of the included structure.
A tree control uses memory allocated from the heap of the process that creates the tree control. The maximum number of items in a tree control is based on the amount of memory available in the heap. Each item takes 64 bytes.