This function returns the anchor block handle of the caller.

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

HWND    hwnd;  /*  Window handle. */
HAB     hab;   /*  Anchor block handle. */

hab = WinQueryAnchorBlock(hwnd);