1IDLOOPC1998.

Object-Oriented Programming

Using C++

CLASS 22File Processing

2IDLOOPC1998.

• Create, read, write and update files

Ob

ject

ives

3IDLOOPC1998.

Creating a Sequential Access File

ios

istream ostream

iostreamifstream ofstream

fstream Fig. 14.3, Pg. 761

4IDLOOPC1998.

ofstream outClientFile(“clients.dat”,

ios::out);if (!outClientFile) {cerr<<“File could not be opened”

<< endl;exit (1); // prototype in stdlib.h

}Fig. 14.4, Pg. 762

5IDLOOPC1998.

cout << “Enter the account, name,and balance.” << endl;<< “Enter EOF to end input.”<< endl << “? ”;

int account;char name[30];float balance;while(cin>>account>>name>>balance){outClientFile << account << ‘ ‘<< name

<< ‘ ‘ << balance << endl;cout << “? ”;}return 0; }

Fig. 14.4, Pg. 762

6IDLOOPC1998.

ofstream outclientFile(“clients.dat”, ios::out);

ofstream outclientFile;

outclientFile.open(“clients.dat”, ios::out);

7IDLOOPC1998.

Opening Modes for Files

• ios::app• Write all output to the end of the

file• ios::ate

• Move to the end of the original file when file is opened. Enable data to be written anywhere in the file

Fig. 14.5, Pg. 763

8IDLOOPC1998.

Opening Modes for Files (Cont’d)

• ios::in• Open a file for input.

• ios::out• Open a file for output.

• ios::trunc• Discard the file’s contents if it

exists (this is also the default action for ios::out) Fig. 14.5, Pg. 763

9IDLOOPC1998.

Opening Modes for Files (Cont’d)

• ios::nocreate• If the file does not exist, the

open operation fails.• ios::noreplace

• If the file exists, the open operation fails.

Fig. 14.5, Pg. 763

10IDLOOPC1998.

Reading Data from a Sequential Access File

11IDLOOPC1998.

int main(){ ifstream (inClientFile(“clients.dat”, ios::in); if (!inClientFile) { cerr << “File could not be opened\n”; exit(1); } int account; char name[30]; double balance; cout << “Account” << setw(13) << “Balance\n”; while (inClientFile >> account >> name >> balance) outputLine(account,name,balance); } void outputLine(int acct, char * name, double bal) { cout << acct << setw(13) << name << bal << endl;

}

12IDLOOPC1998.

Read sequentially from a file, selectively displaying records

13IDLOOPC1998.

enum RequestType { ZERO_BALANCE =1, CREDIT_BALANCE, DEBIT_BALANCE, END);

int main(){ ifstream (inClientFile(“clients.dat”, ios::in); if (!inClientFile) { cerr << “File could not be opened\n”; exit(1); } int request, account; char name[30]; double balance; cout << “Enter request\n”; cout << “1 List accounts with zero balances\n”; cout << “2 List accounts with credit balances\n”; cout << “4 – End of run”; request = getRequest();

14IDLOOPC1998.

while ( request != END) { switch (request) { case: ZERO_BALANCE; cout << “\nAccounts with zero” << “ balances:\n”; break; case: CREDIT_BALANCE: cout << “\nAccounts with credit” << “balances\n”; }// end of switch inClientFile >> account >> name >> balance; while (!inClientFile.eof()) { if (shouldDisplay (request,balance)) outputLine(account,name,balance); inClientFile >> account >> name >> balance; }

15IDLOOPC1998.

inClientFile.clear(); inClientFile.seekg(0); request = getRequest();} cout << “End of run”; return 0;}

16IDLOOPC1998.

void outputLine(int acct, char * name, double bal) { cout << acct << setw(13) << name << bal << endl; }bool shouldDisplay(int type, double balance){ if (type == CREDIT_BALANCE && balance < 0) return true;

if (type == ZERO_BALANCE && balance == 0) return true;return false;

}

17IDLOOPC1998.

int getRequest() { int request; do { cin >> request; } while ( request < ZERO_BALANCE && request > END}; }

18IDLOOPC1998.

Creating a Random Access File

AdamsJonesSmith

19IDLOOPC1998.

Creating a Random Access File

AdamsJonesSmith

add Davis

20IDLOOPC1998.

Creating a Random Access File

AdamsJonesSmith

AdamsDavisJonesSmith

add Davis

21IDLOOPC1998.

Creating a Random Access File

Adamsadd Adams

22IDLOOPC1998.

Creating a Random Access File

Adams

Smith

add Adamsadd Smith

23IDLOOPC1998.

Creating a Random Access File

AdamsDavis

Smith

add Adamsadd Smithadd Davis

24IDLOOPC1998.

Creating a Random Access File

AdamsDavisJonesSmith

add Adamsadd Smithadd Davisadd Jones

25IDLOOPC1998.

File Processing and String Stream I/O

Fig. 14.11Page 774

26IDLOOPC1998.

struct clientData

{ int accountNumber; char lastName[15]; char firstName[10]; double balance;

} ;

#include “clntdata.h” // above structure int main() { ofstream outCredit(“credit.dat”, ios::binary); if (!outCredit) { cerr< “File could not be opened”; exit(1); }

27IDLOOPC1998.

clientData blankClient = { 0, “”, “”, 0.0);for (int I = 0; I < 100; I++) outCredit.write((char *) (&blankClient), sizeof( clientData));

return 0;

}

28IDLOOPC1998.

File Processing and String Stream I/O

Fig. 14.12

Page 775-776

29IDLOOPC1998.

#include “clntdata.h” // above structure int main() { ofstream outCredit(“credit.dat”, ios::binary); if (!outCredit) { cerr< “File could not be opened”; exit(1); } cout << “enter account number” << “(1 to 100, 0 to end input)\n”; clientData client; cin >> client.accountNumber;

30IDLOOPC1998.

while (client.accountNumber > 0 && client.accountNumber <=100) { cout << “enter lastname, firstname,” << “balance\n”; cin >> client.lastName >> client.firstName >> client.balance; outCredit.seekp(client.accountNumber –1)* sizeof(clientData)); outCredit.write( (char *) (&client), sizeof (clientData)); cout << “enter account number”; cin >> client.accountNumber; }

return 0; }

31IDLOOPC1998.

Q & A