This function subclasses the indicated window by replacing its window procedure with another window procedure, specified by pNewWindowProc.

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

HWND     hwnd;            /*  Handle of window that is being subclassed. */
PFNWP    pNewWindowProc;  /*  New window procedure. */
PFNWP    pOldWindowProc;  /*  Old window procedure. */

pOldWindowProc = WinSubclassWindow(hwnd, pNewWindowProc);