Some utilities for C arrays

array.h

#pragma once
#include <assert.h>

#define must_be_array(a)\
    _Pragma("GCC diagnostic push")\
    _Pragma("GCC diagnostic error \"-Wincompatible-pointer-types\"")\
    ((void)sizeof(((char(*)(typeof(a[0])(*)[sizeof(a)/sizeof(a[0])]))0)(&a)))\
    _Pragma("GCC diagnostic pop")\

// returns the length of the provided array
#define lengthof(a) (must_be_array(a),(sizeof(a)/sizeof(a[0])))

// returns a pointer after the last element of the array
#define endof(a) (must_be_array(a),(&a)[1])