// Clause: 6.5.6/6.5.7 — Forming a pointer one-before the first element of an array and dereferencing is undefined.
#include <stdio.h>
int main(void){
    int a[2] = {1,2};
    int *p = &a[0] - 1; // before first
    int v = *p; // UB
    printf("%d\n", v);
    return 0;
}