https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70619
Bug ID: 70619 Summary: Wrong warning with VLA, comma and sizeof Product: gcc Version: 6.0 Status: UNCONFIRMED Severity: normal Priority: P3 Component: c Assignee: unassigned at gcc dot gnu.org Reporter: ch3root at openwall dot com Target Milestone: --- Compiling the program: int main() { int a[1][(0, 1)]; int i = 0; sizeof a[i++]; } gives such warnings: $ gcc -Wall example.c example.c: In function ‘main’: example.c:3:14: warning: left-hand operand of comma expression has no effect [-Wunused-value] int a[1][(0, 1)]; ^ example.c:5:10: warning: right-hand operand of comma expression has no effect [-Wunused-value] sizeof a[i++]; ~~~~~~~^~~~~~ The first one is fine but the second one is wrong and confusing.