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結構體對齊問題

//定義的結構體如下：

typedef struct arp_header{

//-----------------------DLC Header----------------------------------------

unsigned char DesMAC[6]; //目標MAC

unsigned char SrcMAC[6]; //源MAC

unsigned short EtherType; //EtherType默認為0x0806是ARP幀的類型值

//-----------------------ARP Frame-----------------------------------------

unsigned short HW_Type; //硬件類型

unsigned short Prot_Type; //上層協議類型

unsigned char HW_Addr_Len; //MAC地址長度

unsigned char Prot_Addr_Len; //IP地址類型

unsigned short Opcode; //操作碼 0x01表示ARP請求包 0x02表示RARP應答包

unsigned char Send_MAC_Addr[6]; //發送方MAC

unsigned long Send_IP_Addr; //發送方IP

unsigned char Targ_MAC_Addr[6];//接收方MAC

unsigned long arg_IP_Addr; //接受方IP

unsigned char padding[18]; //填充數據

}ARPHEADER,*PARPHEADER;

填充：

m_ARPHdr = new ARPHEADER;

//--------------------------------填充ARP頭--------------------------------

m_ARPHdr->DesMAC[0] = 0Xff;

m_ARPHdr->DesMAC[1] = 0Xff;

m_ARPHdr->DesMAC[2] = 0Xff;

m_ARPHdr->DesMAC[3] = 0Xff;

m_ARPHdr->DesMAC[4] = 0Xff;

m_ARPHdr->DesMAC[5] = 0Xff;

m_ARPHdr->SrcMAC[0] = 0X00;

m_ARPHdr->SrcMAC[1] = 0X08;

m_ARPHdr->SrcMAC[2] = 0X02;

m_ARPHdr->SrcMAC[3] = 0XDB;

m_ARPHdr->SrcMAC[4] = 0X3B;

m_ARPHdr->SrcMAC[5] = 0X95;

m_ARPHdr->EtherType = 0X0608;

// m_ARPHdr->

m_ARPHdr->HW_Type =0X0100; //硬件類型

m_ARPHdr->Prot_Type = 0X0008; //上層協議類型

m_ARPHdr->HW_Addr_Len = 0X06; //MAC地址長度

m_ARPHdr->Prot_Addr_Len =0X04; //IP地址類型

m_ARPHdr->Opcode = 0X0100; //操作碼 0x01表示ARP請求包 0x02表示RARP應答包

// m_ARPHdr->Send_MAC_Addr[6]; //發送方MAC

m_ARPHdr->Send_MAC_Addr[0] = 0X00;

m_ARPHdr->Send_MAC_Addr[1] = 0X08;

m_ARPHdr->Send_MAC_Addr[2] = 0X02;

m_ARPHdr->Send_MAC_Addr[3] = 0XDB;

m_ARPHdr->Send_MAC_Addr[4] = 0X3B;

m_ARPHdr->Send_MAC_Addr[5] = 0X95;

m_ARPHdr->Send_IP_Addr = inet_addr("192.168.11.162"); //發送方IP

// m_ARPHdr->Targ_MAC_Addr[6];//接收方MAC

m_ARPHdr->Targ_MAC_Addr[0] = 0X00;

m_ARPHdr->Targ_MAC_Addr[1] = 0X00;

m_ARPHdr->Targ_MAC_Addr[2] = 0X00;

m_ARPHdr->Targ_MAC_Addr[3] = 0X00;

m_ARPHdr->Targ_MAC_Addr[4] = 0X00;

m_ARPHdr->Targ_MAC_Addr[5] = 0X00;

m_ARPHdr->arg_IP_Addr = inet_addr("192.168.11.154"); //接受方IP

//m_ARPHdr->padding[18] ; //填充數據

memset(&(m_ARPHdr->padding[0]),0,18);

//填充后m_ARPHdr 值如下：

//FF FF FF FF FF FF 00 08 02 DB 3B 95 08 06 00 01 08 00 06 04 00 01 00 08 02 DB 3B 95 C0 A8 0B A2 00 00 00 00 00 00 C0 A8 0B 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

//轉換：

u_char* packet = (u_char*)m_ARPHdr;

//轉換后packet等于

//FF FF FF FF FF FF 00 08 02 DB 3B 95 08 06 00 01 08 00 06 04 00 01 00 08 02 DB 3B 95 C0 A8 0B A2 00 00 00 00 00 00 CD CD C0 A8 0B 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

//而且還有一個問題：

int n = sizeof(ARPHEADER);

//等于64；而不是60

為什么C0 A8 0B 02前怎么不是CD CD

posted on 2008-05-25 21:50 isabc 閱讀(620) 評論(1) 編輯收藏引用所屬分類: BUG分析

#pragma pack(push)
#pragma pack(1)
typedef struct arp_header{
//-----------------------DLC Header----------------------------------------
unsigned char DesMAC[6]; //目標MAC
unsigned char SrcMAC[6]; //源MAC
unsigned short EtherType; //EtherType默認為0x0806是ARP幀的類型值
//-----------------------ARP Frame-----------------------------------------
unsigned short HW_Type; //硬件類型
unsigned short Prot_Type; //上層協議類型
unsigned char HW_Addr_Len; //MAC地址長度
unsigned char Prot_Addr_Len; //IP地址類型
unsigned short Opcode; //操作碼 0x01表示ARP請求包 0x02表示RARP應答包

unsigned char Send_MAC_Addr[6]; //發送方MAC
unsigned long Send_IP_Addr; //發送方IP
unsigned char Targ_MAC_Addr[6];//接收方MAC
unsigned long arg_IP_Addr; //接受方IP
unsigned char padding[18]; //填充數據
}ARPHEADER,*PARPHEADER;
#pragma pack(pop)
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# re: 結構體對齊問題 2008-05-25 21:51 isabc

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