The following expression violates the syntax but is not diagnosed and rejected with -pedantic-errors, for C90 or C99:
extern int x; #if #foo #endif -- Summary: Invalid syntax in PP expressions not diagnosed in strict mode Product: gcc Version: 4.1.3 Status: UNCONFIRMED Severity: normal Priority: P3 Component: preprocessor AssignedTo: unassigned at gcc dot gnu dot org ReportedBy: neil at gcc dot gnu dot org http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35312