关于union

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
union cluster
{
    int a[1];
    char b;
    char c;
};
int main()
{
    union cluster *p; 
    p = malloc(3*sizeof(union cluster));
    int a[3] = {6,7,8};
    memcpy(p,a,sizeof(a));
    printf("%d\n",(p+0)->a[0]);
    printf("%d\n",(p+1)->a[0]);
    printf("%d\n",(p+2)->a[0]);
}