https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88817
Bug ID: 88817 Summary: Diagnostics improvement: Does not detect attempt to use void expression in some cases. Product: gcc Version: 9.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: anders.granlund.0 at gmail dot com Target Milestone: --- Test case (prog.c): extern void v; int main(void) { _Generic(v, default: 0); } Compilation command line: gcc prog.c -Wall -Wextra -std=c11 -pedantic-errors Observed behaviour: No error messages outputed. Possible improvement: The program has undefined behaviour because it attempts to use the void expression v (as the controlling expression of _Generic). Since GCC detects attempts to use void expressions in other case it would be good if it detected it in this case also.