Should clang and gcc produce a diagnostic message when a program does pointer arithmetic on a function pointer?

Question

This program compiles without errors, for example with clang -Wall -std=c11 a.c and gcc -Wall -std=c11 a.c. Is this a bug in clang and gcc? Because ari

Answer 1

Add the -Wpointer-arith flag to produce warnings

a.c:8:22: warning: arithmetic on a pointer to the function type 'void (void)' is a GNU extension [-Wpointer-arith]
    printf("%p\n", p + 1);
                   ~ ^

From GNU documentation

In GNU C, addition and subtraction operations are supported on pointers to void and on pointers to functions. This is done by treating the size of a void or of a function as 1.

Clang -Wpointer-arith documentation

warning: arithmetic on a pointer to the function type B is a GNU extension

Answer 2

Function pointer arithmetic is a gcc extension also implemented by clang.

To invoke standards compliance you need

gcc -std=c11 -pedantic ...
clang -std=c11 -pedantic ...