关于字节对齐

下图是从原文摘抄过来：

数据类型	16位编译器	32位编译器	64位编译器
char	1字节	1字节	1字节
char*	2字节	4字节	8字节
short int	2字节	2字节	2字节
int	2字节	4字节	4字节
unsigned int	2字节	4字节	4字节
float	4字节	4字节	4字节
double	8字节	8字节	8字节
long	4字节	4字节	8字节
long long	8字节	8字节	8字节
unsigned long	4字节	4字节	8字节

#include <QApplication>
#include <iostream>
#include<stddef.h>
using namespace std;



#ifndef BYTE_8
#define BYTE_8 1
#endif

#ifndef BYTE_4
#define BYTE_4 1
#endif


#undef BYTE_8

#ifdef BYTE_4
#pragma pack(4)
#endif

#ifdef BYTE_8
#pragma pack(8)
#endif



typedef struct test_32
{
    char a;
    char d;
    double c;
    
}test_32;

struct st1
{
    char a ;
    int  b ;
    short c ;
};

struct st2
{
    short c ;
    char  a ;
    int   b ;
};

#ifdef BYTE_4
typedef struct Args
{
    char ch; //1+3 = 4
    double d; // 8
    short st; //2
    char rs[9]; //9+3 = 12
    int i; //4 +4 +8 +12=28
} args;

typedef struct Argsa
{
    char ch; //1+3 = 4；
    Args test; //28
    char jd[10]; //12
    int i; //4 + 4+ 12 +28 = 48
}arga;

#endif

#ifdef BYTE_8
typedef struct Args
{
    char ch; //1+7 = 8
    double d; // 8
    short st; //2
    char rs[9]; //9+3 = 12
    int i; //4 +8 +8 +12= 32
} args;

typedef struct Argsa
{
    char ch; //1+7 = 8；
    Args test; //32
    char jd[10]; //10+2= 12
    int i; //4 + 8+ 32 +12 = 56
}arga;

#endif

typedef struct __test_arr
{
    char ch;
    double dd;
    char jd[9];
    int i;
}test_arr;

#ifdef BYTE_4
typedef struct __ArgsP
{
    int i; //4
    double d; //8
    char *p; //8 指针64位机器上默认8字节对齐,不管是否指定了4字节对齐规则
    char ch; //4
    int *pi; //8 +4 + 8 +8+4 = 32
}ArgsP;
#endif

#ifdef BYTE_8
typedef struct __ArgsP
{
    int i; //8
    double d; //8
    char *p; //8 指针64位机器上默认8字节对齐
    char ch; //8
    int *pi; //8 指针64位机器上默认8字节对齐
}ArgsP;
#endif


struct m
{
    int a;
    short b;
    int c;
};


int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    
    cout<<"sizeof(st1) -> "<<sizeof(st1)<<endl;
    cout<<"sizeof(st2) -> "<<sizeof(st2)<<endl;
    cout<<"sizeof(test_32) -> "<<sizeof(test_32)<<endl;
    
    
    cout<<"Args:"<<sizeof(args)<<endl;
    cout<<"test_arr:"<<sizeof(test_arr)<<endl;
    cout<<"Argsa:"<<sizeof(arga)<<endl;
    cout<<"ArgsP:"<<sizeof(ArgsP)<<endl;
    
    
    
    cout <<"struct m size:"<< sizeof(m) << endl;
    cout << endl;
    int offset_b = offsetof(struct m, a);// 获得成员a相对于m储存地址的偏移量
    int offset_b1 = offsetof(struct m, b);// 获得成员b相对于m储存地址的偏移量
    int offset_b2 = offsetof(struct m, c);// 获得成员c相对于m储存地址的偏移量
    
    cout <<"a offset relative to m storage address:"<< offset_b << endl;
    cout << "b offset relative to m storage address:" << offset_b1 << endl;
    cout << "c offset relative to m storage address:" << offset_b2 << endl;
    
    
    
    return a.exec();
}

根据原作者写的，自己进行了一遍理解。