This function copies the window class name, as a null-terminated string, into a buffer.

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

HWND    hwnd;       /*  Window handle. */
LONG    lLength;    /*  Length of PCHBuffer. */
PCH     PCHBuffer;  /*  Class name. */
LONG    lRetLen;    /*  Returned class name length. */

lRetLen = WinQueryClassName(hwnd, lLength,
            PCHBuffer);