The C++ frontend accepts the following invalid code snippet since at least GCC 2.95.3:
============================== void foo(void = 0); void bar() { foo(); } ============================== -- Summary: Default argument for void parameter accepted Product: gcc Version: 4.2.0 Status: UNCONFIRMED Keywords: accepts-invalid, monitored Severity: normal Priority: P3 Component: c++ AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: reichelt at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27423