结构体（Union）内存分配

#include <stdio.h>
#include <iostream>
using namespace std;

union U1
{
char s[9]; //偏移为0
int n;	   //偏移为0
double d;  //偏移为0
};

union U2
{
char s[5];
int n;
double d;
};

int main(int argc, char *argv[])
{
U1 u1;
U2 u2;
u1.n = 0x010203;

printf("sizeof(U1) = %d\n", sizeof(U1));
printf("sizeof(U1) = %d\n", sizeof(U2));
printf("addr(u1)                    = 0x%x\n", &u1);
printf("addr(u1.s) %% sizeof(double) = 0x%x %% %d = %d\n", &u1.s, sizeof(double), (unsigned long)(&u1.s) % (sizeof(double)));
printf("addr(u1.n) %% sizeof(int)    = 0x%x %% %d = %d\n", &u1.n, sizeof(int), (unsigned long)(&u1.n) % (sizeof(int)));
printf("addr(u1.d) %% sizeof(char)   = 0x%x %% %d = %d\n", &u1.d, sizeof(char), (unsigned long)(&u1.d) % (sizeof(char*)));
printf("--------------------------------------\n");

system("pause");
return 0;
}