seekg.cpp

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// seekg.cpp
// seeks particular person in file
#include <fstream>                //for file streams
#include <iostream>
using namespace std;
////////////////////////////////////////////////////////////////
class person                      //class of persons
   {
   protected:
      char name[80];              //person's name
      int age;                    //person's age
   public:
      void getData()              //get person's data
         {
         cout << "\n   Enter name: "; cin >> name;
         cout << "   Enter age: "; cin >> age;
         }
      void showData(void)         //display person's data
         {
         cout << "\n   Name: " << name;
         cout << "\n   Age: " << age;
         }
   };
////////////////////////////////////////////////////////////////
int main()
   {
   person pers;                   //create person object
   ifstream infile;               //create input file 
   infile.open("GROUP.DAT", ios::in | ios::binary);  //open file 

   infile.seekg(0, ios::end);     //go to 0 bytes from end
   int endposition = infile.tellg();        //find where we are
   int n = endposition / sizeof(person);    //number of persons
   cout << "\nThere are " << n << " persons in file";

   cout << "\nEnter person number: ";
   cin >> n;
   int position = (n-1) * sizeof(person);  //number times size
   infile.seekg(position);        //bytes from start
                                  //read one person
   infile.read( reinterpret_cast<char*>(&pers), sizeof(pers) );
   pers.showData();               //display the person
   cout << endl;
   return 0;
   }