empl_io.cpp

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// empl_io.cpp
// performs file I/O on employee objects
// handles different sized objects
#include <fstream>            //for file-stream functions
#include <iostream>
#include <typeinfo>           //for typeid()
using namespace std;
#include <process.h>          //for exit()

const int LEN = 32;           //maximum length of last names
const int MAXEM = 100;        //maximum number of employees

enum employee_type {tmanager, tscientist, tlaborer};
////////////////////////////////////////////////////////////////
class employee                //employee class
   {
   private:
      char name[LEN];         //employee name
      unsigned long number;   //employee number
      static int n;           //current number of employees
      static employee* arrap[];  //array of ptrs to emps
   public:
      virtual void getdata()
         {
         cin.ignore(10, '\n');
         cout << "   Enter last name: "; cin >> name;
         cout << "   Enter number: ";      cin >> number;
         }
      virtual void putdata()
         {
         cout << "\n   Name: " << name;
         cout << "\n   Number: " << number;
         }
      virtual employee_type get_type();  //get type
      static void add();      //add an employee
      static void display();  //display all employees
      static void read();     //read from disk file
      static void write();    //write to disk file
   };
//--------------------------------------------------------------
//static variables
int employee::n;              //current number of employees
employee* employee::arrap[MAXEM];  //array of ptrs to emps
////////////////////////////////////////////////////////////////
//manager class
class manager : public employee
   {
   private:
      char title[LEN];        //"vice-president" etc.
      double dues;            //golf club dues
   public:
      void getdata()
         {
         employee::getdata();
         cout << "   Enter title: ";          cin >> title;
         cout << "   Enter golf club dues: "; cin >> dues;
         }
      void putdata()
         {
         employee::putdata();
         cout << "\n   Title: " << title;
         cout << "\n   Golf club dues: " << dues;
         }
   };
////////////////////////////////////////////////////////////////
//scientist class
class scientist : public employee
   {
   private:
      int pubs;               //number of publications
   public:
      void getdata()
         {
         employee::getdata();
         cout << "   Enter number of pubs: "; cin >> pubs;
         }
      void putdata()
         {
         employee::putdata();
         cout << "\n   Number of publications: " << pubs;
         }
   };
////////////////////////////////////////////////////////////////   
//laborer class
class laborer : public employee
   {
   };
////////////////////////////////////////////////////////////////
//add employee to list in memory
void employee::add()
   {
   char ch;
   cout << "'m' to add a manager"
           "\n's' to add a scientist"
           "\n'l' to add a laborer"
           "\nEnter selection: ";
   cin >> ch;
   switch(ch)
      {                       //create specified employee type
      case 'm': arrap[n] = new manager;   break;
      case 's': arrap[n] = new scientist; break;
      case 'l': arrap[n] = new laborer;   break;
      default: cout << "\nUnknown employee type\n"; return;
      }
   arrap[n++]->getdata();     //get employee data from user
   }
//--------------------------------------------------------------
//display all employees
void employee::display()
   {
   for(int j=0; j<n; j++)
      {
      cout  << (j+1);           //display number
      switch( arrap[j]->get_type() )   //display type
         {
         case tmanager:    cout << ". Type: Manager";   break;
         case tscientist:  cout << ". Type: Scientist"; break;
         case tlaborer:    cout << ". Type: Laborer";   break;
         default: cout << ". Unknown type";
         }
      arrap[j]->putdata();    //display employee data
      cout << endl;
      }
   }
//--------------------------------------------------------------
//return the type of this object
employee_type employee::get_type()
   {
   if( typeid(*this) == typeid(manager) )
      return tmanager;
   else if( typeid(*this)==typeid(scientist) )
      return tscientist;
   else if( typeid(*this)==typeid(laborer) )
      return tlaborer;
   else
      { cerr << "\nBad employee type"; exit(1); }
   return tmanager;
   }
//--------------------------------------------------------------
//write all current memory objects to file
void employee::write()
   {
   int size;
   cout << "Writing " << n << " employees.\n";
   ofstream ouf;              //open ofstream in binary
   employee_type etype;       //type of each employee object

   ouf.open("EMPLOY.DAT", ios::trunc | ios::binary);
   if(!ouf)
      { cout << "\nCan't open file\n"; return; }
   for(int j=0; j<n; j++)     //for every employee object
      {                       //get its type
      etype = arrap[j]->get_type();
                              //write type to file
      ouf.write( (char*)&etype, sizeof(etype) );
      switch(etype)           //find its size
         {
         case tmanager:   size=sizeof(manager); break;
         case tscientist: size=sizeof(scientist); break;
         case tlaborer:   size=sizeof(laborer); break;
         }                    //write employee object to file
      ouf.write( (char*)(arrap[j]), size );
      if(!ouf)
         { cout << "\nCan't write to file\n"; return; }
      }
   }
//--------------------------------------------------------------
//read data for all employees from file into memory
void employee::read()
   {
   int size;                  //size of employee object
   employee_type etype;       //type of employee
   ifstream inf;              //open ifstream in binary
   inf.open("EMPLOY.DAT", ios::binary);
   if(!inf)
      { cout << "\nCan't open file\n"; return; }
   n = 0;                     //no employees in memory yet
   while(true)
      {                       //read type of next employee
      inf.read( (char*)&etype, sizeof(etype) );
      if( inf.eof() )         //quit loop on eof
         break;
      if(!inf)                //error reading type
         { cout << "\nCan't read type from file\n"; return; }
      switch(etype)
         {                    //make new employee
         case tmanager:       //of correct type
            arrap[n] = new manager;
            size=sizeof(manager);
            break;
         case tscientist:
            arrap[n] = new scientist;
            size=sizeof(scientist);
            break;
         case tlaborer:
            arrap[n] = new laborer;
            size=sizeof(laborer);
            break;
         default: cout << "\nUnknown type in file\n"; return;
         }                    //read data from file into it
      inf.read( (char*)arrap[n], size  );
      if(!inf)                //error but not eof
         { cout << "\nCan't read data from file\n"; return; }
      n++;                    //count employee
      }  //end while
   cout << "Reading " << n << " employees\n";
   }
////////////////////////////////////////////////////////////////
int main()
   {
   char ch;
   while(true)
      {
      cout << "'a' -- add data for an employee"
              "\n'd' -- display data for all employees"
              "\n'w' -- write all employee data to file"
              "\n'r' -- read all employee data from file"
              "\n'x' -- exit"
              "\nEnter selection: ";
      cin >> ch;
      switch(ch)
         {
         case 'a':            //add an employee to list
            employee::add(); break;
         case 'd':            //display all employees
            employee::display(); break;
         case 'w':            //write employees to file
            employee::write(); break;
         case 'r':            //read all employees from file
            employee::read(); break;
         case 'x': exit(0);   //exit program
         default: cout << "\nUnknown command";
         }  //end switch
      }  //end while
   return 0;
   }  //end main()