程式設計講義----PGM10-09.cpp

[Kenad (..大拇指腫歪歪..)]

#include <fstream.h>
#include <iomanip.h>
#include <stdlib.h>

const int MAXCHARS = 21;
char old_master[MAXCHARS] = "oldbook.mas";  // here are the files we will be
char new_master[MAXCHARS] = "newbook.mas";  // working with
char transactions[MAXCHARS] = "book.trn";

void do_update(void);

int main()
{
  do_update();

  return 0;
}

// update function
// precondition: both a master file named oldbook.mas and
//             : a transaction file named book.trn exist on
//             : the current directory
//             : and both files are in date order
// postcondition: a new master file named newbook.mas is created

void do_update(void)
{
  const int MAXDATE = 8;
  int idmast, idtrans, balance, sold, returned, bought;
  int ch;
  char date[MAXDATE];
  ifstream oldmast, trans;
  ofstream newmast;

     // open and check the old_master file
  oldmast.open(old_master);
  if (oldmast.fail())
  {
    cout << "\nThe input file " << old_master <<  "was not successfully opened"
         << "\n Please check that the file currently exists." << endl;
    exit(1);
  }
     // open and check the new_master file
  newmast.open(new_master);
  if (newmast.fail())
  {
    cout << "\nFailed to open the new master file " << new_master
         << " for output." << endl;
    exit(1);
  }
     // open and check the transaction file
  trans.open(transactions);
  if (trans.fail())
  {
    cout << "\nThe input file " << trans << " was not successfully opened"
         << "\n Please check that the file currently exits." << endl;
    exit(1);
  }
       // read the first old master file record
  oldmast >> idmast >> balance;
  while( (ch = trans.peek()) != EOF)
  {
       // read one transactions record
     trans >> idtrans >> date >> sold >> returned >> bought;
       // if no match keep writing and reading the master file
    while (idtrans > idmast)
    {
      newmast << '\n' << idmast << setw(6) << balance;
      oldmast >> idmast >> balance;
    }
    balance = balance + bought - sold + returned;
  }
     // write the last updated new master file
  newmast << '\n' << idmast << setw(6) << balance;
     // write any remaining old master records to the new master
  while ( (ch = oldmast.peek()) != EOF)
  {

    oldmast >> idmast >> balance;
    newmast << '\n' << idmast << setw(6) << balance;
  }

  oldmast.close();
  newmast.close();
  trans.close();
  cout << "\n....File update complete...\n";

  return;
}

--
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