This function returns the handle of a window that has a specified relationship to a specified window.

#define INCL_WINWINDOWMGR /* Or use INCL_WIN, INCL_PM, */
#include <os2.h>

HWND    hwnd;         /*  Handle of window to query. */
LONG    lCode;        /*  Type of window information. */
HWND    hwndRelated;  /*  Window handle. */

hwndRelated = WinQueryWindow(hwnd, lCode);