Ethernet帧结构解析程序C++

#include"stdafx.h"

#include

#include

#include

using namespace std;

const int MAXLENGTH = 1500;

const int MINLENGTH = 46;

const char destination[] =

{

char(0xFF), char(0xFF), char(0xFF),

char(0xFF), char(0xFF), char(0xFF)

};

const char source[] =

{

char(0x00), char(0x16), char(0x76),

char(0xB4), char(0xE4), char(0x77)

};

int main()

{

fstream infile;

//fstream outfile;

string data;

//outfile.open("FrameParse.txt", ios::out|ios::binary|ios::trunc);

infile.open("南开简介.txt");

getline(infile, data);

//计算封帧个数

int truelen = data.length(); //数据的真实长度

int length = data.length();

int frameTotal = 0; //总的帧的个数

if (length>MAXLENGTH)

{

frameTotal = length / MAXLENGTH;

if (length%MAXLENGTH)

frameTotal++;

cout << "数据字段大于1500B，将封装成" << frameTotal << "个帧……" << endl;

}

else if (length

{

while (length

{

data += '0';

//cout << data << endl;

length++;

//cout << data.length() << endl;

}

frameTotal = 1;

cout << "数据字段小于46B，将封装成1个帧……" << endl;

}

else if (length == MINLENGTH)

{

frameTotal = 1;

cout << "数据字段等于46B，将封装成1个帧……" << endl;

}

else if (length>MINLENGTH&&length

{

frameTotal = 1;

cout << "数据字段介于46B和1500B之间，将封装成1个帧……" << endl; }

else

{

frameTotal = 1;

cout << "数据字段等于1500B，将封装成1个帧……" << endl;

}

cout << endl;

//cout << truelen << endl;

//cout << length << endl;

string divideStr; //本次拆分好的数据

string leftStr = data; //剩余未封装的数据

for (int i = 1; i <= frameTotal; i++)

{

fstream outfile;

char filename[10];

sprintf_s(filename,"%d.txt",i);

outfile.open(filename, ios::out | ios::binary | ios::trunc);

outfile.seekg(0, ios::end); //将文件指针移到文件末尾

for (int j = 0; j<7; j++) //写入7字节的前导码

outfile.put((char)0xaa);

outfile << endl;

outfile.put((char)0xab); //写入1字节的帧前定界符

outfile << endl;

streampos nCrcs = outfile.tellp(); //获得开始CRC校验的位置

outfile.write(destination, sizeof(destination)); //写入6字节的目的地址

outfile << endl;

outfile.write(source, sizeof(source)); //写入6字节的源地址

outfile << endl;

if (truelen >= MAXLENGTH)

{

divideStr = leftStr.substr(0, MAXLENGTH);

outfile.put(char(MAXLENGTH / 256)); //写入2字节的长度字段

outfile.put(char(MAXLENGTH % 256));

outfile << divideStr << endl; //写入数据字段

cout << "长度字段：" << hex << MAXLENGTH << dec << "(" << MAXLENGTH<< ")" << endl;

cout << "数据字段：" << divideStr << endl;

leftStr = leftStr.substr(MAXLENGTH, length);

truelen = leftStr.length();

}

else

{

outfile.put(char(truelen / 256)); //写入2字节的长度字段

outfile.put(char(truelen % 256));

outfile << leftStr << endl; //写入数据字段

cout << "长度字段："<< hex << truelen << dec << "("<< truelen << ")"<< endl;

cout << "数据字段：" << leftStr << endl;

}

streampos nCrc = outfile.tellp(); //获得帧校验字段的位置

outfile.put(char(0x00)); //数据后补1字节的0，用于CRC计算

int total = nCrc - nCrcs; //获得需要进行CRC计算的数据长度

outfile.seekg(nCrcs, ios::beg); //将文件指针指向目的地址

unsigned char crc = 0; //初始化CRC余数为0

while (total--)

{

char temp;

outfile.get(temp);

for (unsigned char i = (unsigned char)0x80; i>0; i >>= 1)

{

if (crc & 0x80)

{

crc <<= 1;

if (temp)

crc ^= 0x01;

crc ^= 0x70;

}

else

{

crc <<= 1;

if (temp&i)

crc ^= 0x01;

}

}

}

outfile.seekp(nCrc, ios::beg); //将文件写指针移到数据字段后

outfile << crc << endl; //将CRC余数写入帧校验字段

cout << "帧校验字段："<< hex << (int)crc << dec << "("<< (int)crc << ")"<< endl;

cout << "第" << i << "个帧封装完毕！" << endl;

cout << endl;

outfile.close();

}

infile.close();

return 0;

}