1. 變數的首地址能夠被其對齊位元組數大小整除。（實際開發中可以無視這條）
2. 每個成員相對首地址的偏移量都是該成員大小的整數倍，如果不是，那麼前一個成員變數補齊
3. 總大小是最大成員大小的整數倍

  1 #include <iostream>
  2 using namespace std;
  3 
  4 struct POINTER
  5 {
  6     void* ptr;
  7 };
  8 
  9 struct A
 10 {
 11     char a;
 12 };
 13 
 14 struct B
 15 {
 16     char a;
 17     char
 
 b;
 18 };
 19 
 20 struct C
 21 {
 22     char a;
 23     int b;
 24     long c;
 25 };
 26 
 27 struct D
 28 {
 29     long c;
 30     char a;
 31     int b;
 32 };
 33 
 34 struct E
 35 {
 36     char a;
 37     long c;
 38     int b;
 39 };
 40 
 41 struct F
 42 {
 43     char a;
 44     long c;
 45
 
     char b;
 46 };
 47 
 48 struct G
 49 {
 50     char a;
 51     long c;
 52     F b;
 53 };
 54 
 55 struct H
 56 {
 57     char a;
 58     char b;
 59     short c;
 60 };
 61 
 62 struct I
 63 {
 64     char a;
 65     char b;
 66     int c;
 67 };
 68 
 69 struct EMPTY_CLASS
 70 {
 71 };
 72 
 73
 
 struct EMPTY_CLASS_WITH_VIRTUAL
 74 {
 75     virtual ~EMPTY_CLASS_WITH_VIRTUAL(){}
 76 };
 77 
 78 #define CALC_STRCUT_SIZE(T) \
 79     std::cout <<"size of type " << #T << " is " << sizeof(T) << std::endl;
 80 
 81 int main(int argc, char** argv)
 82 {
 83     printf("sizeof(long) : %d\n", sizeof(long));
 84     CALC_STRCUT_SIZE(A)
 85     CALC_STRCUT_SIZE(B)
 86     CALC_STRCUT_SIZE(C)
 87     CALC_STRCUT_SIZE(D)
 88     CALC_STRCUT_SIZE(E)
 89     CALC_STRCUT_SIZE(F)
 90     CALC_STRCUT_SIZE(G)
 91     CALC_STRCUT_SIZE(H)
 92     CALC_STRCUT_SIZE(I)
 93 
 94     CALC_STRCUT_SIZE(EMPTY_CLASS)
 95     CALC_STRCUT_SIZE(EMPTY_CLASS_WITH_VIRTUAL)
 96 
 97     CALC_STRCUT_SIZE(char*)
 98     CALC_STRCUT_SIZE(short*)
 99     CALC_STRCUT_SIZE(int*)
100     CALC_STRCUT_SIZE(long*)
101     CALC_STRCUT_SIZE(void*)
102     CALC_STRCUT_SIZE(F*)
103     CALC_STRCUT_SIZE(POINTER)
104     return 0;
105 }