#include "stdafx.h"

 #include<iostream>

 #include<string>

 #include<fstream>

 using namespace std;

 class Rectangle

 {

 private:

     double length, width;

 public:

     Rectangle(double l, double w);

 };

 Rectangle::Rectangle(double l, double w) :length(l), width(w)

 {}

 int main()

 {

     Rectangle rect(20.0, 10.3);

     ofstream out("a.dat", ios_base::binary);     //文件的输出

     if (out.is_open())                           //如果打开成功

     {

         out.write((char*)&rect, sizeof(Rectangle));//把Rectangle类的rect成员写入

         out.close();                             //注意:此步一定不能省

     }

     char* buf = new char[sizeof(Rectangle)];     //缓冲区

     ifstream in("a.dat", ios_base::binary);      //文件的写入

     if (in.is_open())                            //如果文件打开成功

     {

         in.read(buf, sizeof(Rectangle));         //从in指定的已打开文件中读取Rectangle字节到buf中

         in.close();                              //注意:此步一定不能省

     }

     return ;

 }

 #include "stdafx.h"

 #include<iostream>

 #include<string>

 #include<fstream>

 using namespace std;

 class Rectangle

 {

 private:

     double length, width;

 public:

     Rectangle(double l, double w);

     void displayArea() { cout << length * width << endl; }

 };

 Rectangle::Rectangle(double l, double w) :length(l), width(w)

 {}

 int main()

 {

     int a[] = { ,,, };

     Rectangle rect(20.0, 10.3);

     ofstream out("a.dat", ios_base::binary);

     if (out.is_open())

     {

         out.write((char*)&rect, sizeof(Rectangle));

         out.write((char*)a,  * sizeof(int));  //对数组来说，数组有n个元素那么后面就是n*sizeof(int)

         out.close();

     }

     char* buf = new char[sizeof(Rectangle)];

     char* buf2 = new char[ * sizeof(int)];

     ifstream in("a.dat", ios_base::binary);

     if (in.is_open())

     {

         in.read(buf, sizeof(Rectangle));

         in.read(buf2, sizeof(int) * );

         int *a = new int[];

         memcpy(a, buf2,  * sizeof(int));

         cout << a[] << endl;

         delete[] a;

         in.close();

         Rectangle* pr = (Rectangle*)buf;

         pr->displayArea();

     }

     delete[] buf;

     return ;

 }

 #include "stdafx.h"

 #include<iostream>

 #include<string>

 #include<fstream>

 using namespace std;

 class Rectangle

 {

 private:

     double length, width;

 public:

     Rectangle(double l, double w);

     void displayArea() { cout << length * width << endl; }

 };

 Rectangle::Rectangle(double l, double w) :length(l), width(w)

 {}

 int main()

 {

     fstream file("a.txt", ios_base::out | ios_base::app);

     if (file.is_open())

     {

         file << "Hello world!";

         file.close();

     }

     file.open("a.txt", ios_base::in);

     if (file.is_open())

     {

         while (file.good())

         {

             string words;

             file >> words;

             cout << words << " ";

         }

         file.close();

         cout << endl;

     }

     return ;

 }