This function adds an atom to an atom table.

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

HATOMTBL    hatomtblAtomTbl;  /*  Atom-table handle. */
PSZ         AtomName;         /*  Atom name. */
ATOM        atom;             /*  Atom value. */

atom = WinAddAtom(hatomtblAtomTbl, AtomName);