C99 6.5.2.3.5 seems to suggest that non-overlapping union members could break conforming code: ``One special guarantee is made in order to simplify the use of

C99 6.5.2.3.5 seems to suggest that non-overlapping union members could break conforming code: ``One special guarantee is made in order to simplify the use of unions: if a union contains several structures that share a common initial sequence (see below), and if the union object currently contains one of these structures, it is permitted to inspect the common initial part of any of them anywhere that a declaration of the complete type of the union is visible. Two structures share a common initial sequence if corresponding members have compatible types (and, for bit-fields, the same widths) for a sequence of one or more initial members.''