The gcc warning options document says the -pedantic option is supposed to give warnings for forbidden extensions out of strict ISO C.

However, when I compile the following code with my gcc version 9.4.0 with -pedantic only, it warns nothing.

#include <stdio.h>
int main(void) {
    int foo;
    typeof(foo) bar = 42;
    printf("%dn", bar);
}

I thought gcc would catch typeof() as an error since it is a gcc extension and not a part of the C17 standard. Only when both -pedantic and -std=c17 were set, instead of the default -std=gnu17, I could find desired warnings (“implicit declaration of function ‘typeof’”).

How does exactly -pedantic work? Is it being “weakly pedantic” without specifying an ISO C version?