/*
 
 不能只計(jì)算大小,關(guān)鍵也得知道怎么排列的,關(guān)系到按字節(jié)取值
 
 
 結(jié)構(gòu)體每個(gè)成員相對(duì)于結(jié)構(gòu)體首地址的偏移量offset都是這個(gè)成員大小的整數(shù)倍
 每個(gè)成員按其類型的對(duì)齊參數(shù)和指定參數(shù)中較小的一個(gè)對(duì)齊
 結(jié)構(gòu)體或者類的自身對(duì)齊值：其成員中自身對(duì)齊值最大的那個(gè)值
  對(duì)齊后的長(zhǎng)度必須是成員中最大的對(duì)齊參數(shù)的整數(shù)倍,這樣在處理數(shù)組時(shí)可以保證每一項(xiàng)都邊界對(duì)齊

 可以指定對(duì)齊值
 
 
 iOS目前環(huán)境下用sizeof取值得到:
 long long  8
 long       8
 int        4
 short      2
 Byte       1
 
 
 
 */

/*
 struct ex
 第一個(gè)成員i offset為0 是int 4字節(jié)的整數(shù)倍
 第二個(gè)成員t offset為4 是char 1字節(jié)的整數(shù)倍
 第三個(gè)成員n 未填充字節(jié)前 offset為5 不符合對(duì)齊,所以t后面會(huì)補(bǔ)3個(gè)字節(jié)
 sizeof的大小是 4 + 1 + 補(bǔ)3 + 4 = 12
 */
typedef struct ex {
    int i;
    char t;
    int n;
}ex;

#pragma pack(1)
typedef struct ex1 {
    int i;
    char t;
    int n;
    char add;
}ex1;               //4 + 1 + 補(bǔ)3 + 4 + 1 +補(bǔ)3 = 16
#pragma pack()      //按一個(gè)字節(jié)對(duì)齊就是 10 了


typedef struct ex2 {
    int i;
    short t;
    short n;
}ex2;               //4 + 2 + 2 = 8

typedef struct ex3 {
    int i;
    short t;
}ex3;               //4 + 2 + 補(bǔ)2 = 8

typedef struct ex4
{
    char c;
    int msTimeStamp;
} ex4;             //1 + 補(bǔ)3 + 4 = 8

typedef struct ex5
{
    char c;
    long msTimeStamp;
} ex5;              //1 + 補(bǔ)7 + 8 = 16


typedef struct ex6
{
    char c;
    long msTimeStamp;
} ex6;              //1 + 補(bǔ)7 + 8 = 16

typedef struct ex7
{
    char c;
    char c1;
    char c2;
    int i;
    long msTimeStamp;
} ex7;              //1 + 1 + 1 + 補(bǔ)1 + 4 (夠8個(gè)了) + 8 = 16

typedef struct ex8
{
    char c;
    char c1;
    char c2;
    int i;
    long msTimeStamp;
} ex8;              //1 + 1 + 1 + 補(bǔ)1 + 4 (夠8個(gè)了) + 8 = 16

//指定一個(gè)字節(jié)對(duì)齊
#pragma pack(1)
typedef struct ex9
{
    char c;
    char c1;
    char c2;
    int i;
    long msTimeStamp; //15
} ex9;
#pragma pack()

typedef struct ex10
{
    char c;
    char c1;
    char c2;
    int i;
    long msTimeStamp;
    int j;
} ex10;         //24  對(duì)比ex8 加了一個(gè)int 后  按最長(zhǎng)的對(duì)齊了 加了一個(gè)8


//注意合理分配結(jié)構(gòu)大小,控制所占內(nèi)存的大小
typedef struct s1
{
    int a;
    short b;
    short c;
} s1;              //4 + 2 + 2 = 8

typedef struct s2
{
    short b;
    int a;
    short c;
} s2;              //2 + 補(bǔ) 2 + 4 + 2 + 補(bǔ)2 = 12
/*
 把結(jié)構(gòu)體賦值后,轉(zhuǎn)成data  測(cè)測(cè)data大小
 
 */