结构体的一些问题
输出怎么是这样的？不是应该相加为40吗？怎么是3+36=39？
还有改成unsigned long addr[8];怎么结果没变啊？？
#include <winsock2.h>
#include <ws2tcpip.h>
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
typedef struct _ipoptionhdr
{
unsigned char code; /*选项类型*/
unsigned char len; /*选项头长度*/
unsigned char ptr; /*地址偏移长度*/
unsigned long addr[9]; /*记录的IP地址列表*/
} IpOptionHeader;
typedef struct _ipoptionhdr1
{
unsigned char code; /*选项类型*/
unsigned char len; /*选项头长度*/
unsigned char ptr; /*地址偏移长度*/
//unsigned long addr[9]; /*记录的IP地址列表*/
} IpOptionHeader1;
typedef struct _ipoptionhdr2
{
//unsigned char code; /*选项类型*/
//unsigned char len; /*选项头长度*/
//unsigned char ptr; /*地址偏移长度*/
unsigned long addr[9]; /*记录的IP地址列表*/
} IpOptionHeader2;
typedef struct _ipoptionhdr3
{
unsigned char code; /*选项类型*/
unsigned char len; /*选项头长度*/
unsigned char ptr; /*地址偏移长度*/
unsigned long addr[8]; /*记录的IP地址列表*/
} IpOptionHeader3;
int main()
{
printf("IpOptionHeader=%d\n",sizeof(IpOptionHeader));
printf("IpOptionHeader1=%d\n",sizeof(IpOptionHeader1));
printf("IpOptionHeader2=%d\n",sizeof(IpOptionHeader2));
printf("IpOptionHeader3=%d\n",sizeof(IpOptionHeader3));
return 0;
}
#include <stdio.h>
#define field_offset(s,f) (int)(&(((struct s *)(0))->f))
struct AD { int a; char b[13]; double c;};
#pragma pack(push)
#pragma pack(1)
struct A1 { int a; char b[13]; double c;};
#pragma pack(2)
struct A2 { int a; char b[13]; double c;};
#pragma pack(4)
struct A4 { int a; char b[13]; double c;};
#pragma pack(8)
struct A8 { int a; char b[13]; double c;};
#pragma pack(16)
struct A16 { int a; char b[13]; double c;};
#pragma pack(pop)
int main() {
printf("AD.a %d\n",field_offset(AD,a));
printf("AD.b %d\n",field_offset(AD,b));
printf("AD.c %d\n",field_offset(AD,c));
printf("\n");
printf("A1.a %d\n",field_offset(A1,a));
printf("A1.b %d\n",field_offset(A1,b));
printf("A1.c %d\n",field_offset(A1,c));
printf("\n");
printf("A2.a %d\n",field_offset(A2,a));
printf("A2.b %d\n",field_offset(A2,b));
printf("A2.c %d\n",field_offset(A2,c));
printf("\n");
printf("A4.a %d\n",field_offset(A4,a));
printf("A4.b %d\n",field_offset(A4,b));
printf("A4.c %d\n",field_offset(A4,c));
printf("\n");
printf("A8.a %d\n",field_offset(A8,a));
printf("A8.b %d\n",field_offset(A8,b));
printf("A8.c %d\n",field_offset(A8,c));
printf("\n");
printf("A16.a %d\n",field_offset(A16,a));
printf("A16.b %d\n",field_offset(A16,b));
printf("A16.c %d\n",field_offset(A16,c));
printf("\n");
return 0;
}
//AD.a 0
//AD.b 4
//AD.c 24
//
//A1.a 0
//A1.b 4
//A1.c 17
//
//A2.a 0
//A2.b 4
//A2.c 18
//
//A4.a 0
//A4.b 4
//A4.c 20
//
//A8.a 0
//A8.b 4
//A8.c 24
//
//A16.a 0
//A16.b 4
//A16.c 24
//
//
