This function sets an unsigned, long integer value into the memory of the reserved window words.

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

HWND     hwnd;   /*  Window handle. */
LONG     index;  /*  Zero-based index of the value to be set. */
ULONG    ul;     /*  Unsigned, long integer value to store in the window words. */
BOOL     rc;     /*  Success indicator. */

rc = WinSetWindowULong(hwnd, index, ul);