doubletos
u.str = doubletos(u.d, 7, *p);
u.str = doubletos(u.d, 16,
mdb_printf("%s", doubletos(u.f, 7, 'e'));
mdb_printf("%s", doubletos(u.d, 7, 'e'));
extern const char *doubletos(double, int, char);