This function sets a pointer 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     lb;    /*  Zero-based index into the window words. */
PVOID    pp;    /*  Pointer value to store in the window words. */
BOOL     rc;    /*  Success indicator. */

rc = WinSetWindowPtr(hwnd, lb, pp);