Ask about struct !!

Ask about struct !! -- Linux general technology-Linux programming and kernel information. The following is a detailed description. There are two struct types:
1. typedef struct _ rcafilelist {
HWNDhwnd;
INT8Ufilelist_status;
INT8Utotal_items;
INT8U focused_item_index;
INT8U first_item_index;
INT8U list_levels;
INT8U title_length;

INT32U deactive_bmp;
INT32U deactive_focused_bmp;
INT32U unselected_bmp;
INT32Uselected_bmp;
INT32Uselected_left_bmp;
INT32Uselected_right_bmp;
INT32Uselected_both_bmp;
INT32Upicked_bmp;
INT32Ufocused_picked_bmp;

INT16U deactive_bmp _type;
INT16U deactive_focused_bmp _type;
INT16U unselected_bmp _type;
Int16uselected_bmp _type;
Int16uselected_left_bmp _type;
Int16uselected_right_bmp _type;
Int16uselected_both_bmp _type;
Int16upicked_bmp _type;
Int16ufocused_picked_bmp _type;

Int16ufilelist_bmp _start_x;
Int16ufilelist_bmp _start_y;
INT16Ufilelist_title_start_x;
INT16Ufilelist_title_start_y;

DRAWINFO list_up_arrow_info;
DRAWINFO list_down_arrow_info;
DRAWINFO filelist_hint_info;
TFILELISTITEM * filelist_items;

GETFILEENTRYS get_next_entrys;
GETFILEENTRYS get_prev_entrys;
CDNEWENTRYcd_new_entry;
GETENTRYFULLNAMEANDTYPEget_entry_full_name;
CDROOTENTRYcd_root_entry;

INT16U index [MAX_INDEX_BAK];
INT16U focus [MAX_INDEX_BAK];
} TFILELIST;
Second:
Typedef struct _ hwnd {
PHWND parent;
PHWND children;
PHWND siblings;
PWNDCLASSpClass;
INT32Ustyle;
RECTwinrect;
CHARSTR win_name [MAX_LENGTH_OF_WIN_CONTROL_NAME];
INT16Uwin_id;
INT8Udraw_info_num;
PDRAWINFOdraw_info;
WINPROCWinProc;
INT32Suserdata;
} HWND;

Then we define: 1. PHWND hwnd;
2. TFILELIST * pList = (TFILELIST *) hwnd;
3. pList-> filelist_hint_info.draw_data = (INT32U) EMPTY_FOLDER_HELP_STR;
The problem is only in the second sentence:
How does one perform internal offset address conversion for forced type conversion between structs?