نظام المحاضرات الالكترونينظام المحاضرات الالكتروني I/O and File management(cont.) Binary and random files.

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 2 Random-Access Files Instant access Want to locate record quickly Airline reservations, ATMs Sequential files must search through each one Random-access files are solution Instant access Insert record without destroying other data Update/delete items without changing other data

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 3 Random-Access Files C++ imposes no structure on files Programmer must create random-access files Simplest way: fixed-length records Calculate position in file from record size and key

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 4 Creating a Random-Access File " " ( char * ) vs ( int ) char * takes 8 bytes (1 for each character + null) int takes fixed number of bytes (perhaps 4) 123 same size in bytes as << operator and write() outFile << number Outputs number ( int ) as a char * Variable number of bytes outFile.write( const char *, size ); Outputs raw bytes Takes pointer to memory location, number of bytes to write Copies data directly from memory into file Does not convert to char *

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 5 Creating a Random-Access File Example outFile.write( reinterpret_cast (&number), sizeof( number ) ); &number is an int * Convert to const char * with reinterpret_cast sizeof(number) Size of number (an int ) in bytes read function similar (more later) Must use write / read between compatible machines Only when using raw, unformatted data Use ios::binary for raw writes/reads

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 6 Creating a Random-Access File Usually write entire struct or object to file Problem statement Credit processing program Store at most 100 fixed-length records Record Account number (key) First and last name Balance Account operations Update, create new, delete, list all accounts in a file Next: program to create blank 100-record file

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 7 clientData. h (1 of 2) 1 // Fig clientData.h 2 // Class ClientData definition used in Fig –Fig #ifndef CLIENTDATA_H 4 #define CLIENTDATA_H 5 #include 6 #include 7 using std::string; 9 class ClientData { 10 public: 11 // default ClientData constructor 12 ClientData( int = 0, string = "", string = "", double = 0.0 ); // accessor functions for accountNumber 15 void setAccountNumber( int ); 16 int getAccountNumber() const; 18 // accessor functions for lastName 19 void setLastName( string ); 20 string getLastName() const;

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 8 clientData. h (2 of 2) 21 // accessor functions for firstName 22 void setFirstName( string ); 23 string getFirstName() const; // accessor functions for balance 26 void setBalance( double ); 27 double getBalance() const; private: 30 int accountNumber; 31 char lastName[ 15 ]; 32 char firstName[ 10 ]; 33 double balance; 35 }; // end class ClientData #endif

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 9 Fig14.4.cpp (1 of 2) 1 // Fig. 14.4cpp 2 // Creating a randomly accessed file. 3 #include 4 using std::cerr; 5 using std::endl; 6 using std::ios; 8 #include 9 using std::ofstream; 11 #include 12 #include "clientData.h" // ClientData class definition 14 int main() { 15 ofstream outCredit( "credit.dat", ios::binary ); 17 // exit program if ofstream could not open file 18 if ( !outCredit ) { 19 cerr << "File could not be opened." << endl; 20 exit( 1 ); 21 } // end if

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 10 fig14_4.cp p (2 of 2) // create ClientData with no information 24 ClientData blankClient; // output 100 blank records to file 27 for ( int i = 0; i < 100; i++ ) 28 outCredit.write( 29 reinterpret_cast ( &blankClient ), 30 sizeof( ClientData ) ); return 0; } // end main

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 11 Writing Data Randomly to a Random- Access File Use seekp to write to exact location in file Where does the first record begin? Byte 0 The second record? Byte 0 + sizeof(object) Any record? (recordNum - 1) * sizeof(object)

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 12 fig14_5.cp p (2 of 4) 19 int main() { 20 int accountNumber; 21 char lastName[ 15 ]; 22 char firstName[ 10 ]; 23 double balance; 25 ofstream outCredit( "credit.dat", ios::binary ); 27 // exit program if ofstream cannot open file 28 if ( !outCredit ) { 29 cerr << "File could not be opened." << endl; 30 exit( 1 ); 31 } // end if 33 cout << "Enter account number " 34 << "(1 to 100, 0 to end input)\n? "; 36 // require user to specify account number 37 ClientData client; 38 cin >> accountNumber; 39 client.setAccountNumber( accountNumber );

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني // user enters information, which is copied into file 41 while ( client.getAccountNumber() > 0 && 42 client.getAccountNumber() <= 100 ) { 44 // user enters last name, first name and balance 45 cout << "Enter lastname, firstname, balance\n? "; 46 cin >> setw( 15 ) >> lastName; 47 cin >> setw( 10 ) >> firstName; 48 cin >> balance; // set record lastName, firstName and balance values 51 client.setLastName( lastName ); 52 client.setFirstName( firstName ); 53 client.setBalance( balance ); // seek position in file of user-specified record 56 outCredit.seekp( ( client.getAccountNumber() - 1 ) * sizeof( ClientData ) ); // write user-specified information in file 59 outCredit.write(reinterpret_cast ( &client ), sizeof( ClientData ) ); fig14_5.cpp (3 of 4)

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 14 fig14_5.cp p (4 of 4) 60 // enable user to specify another account number 61 cout << "Enter account number\n? "; 62 cin >> accountNumber; 63 client.setAccountNumber( accountNumber ); } // end while return 0; } // end main

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 15 fig14_5.cpp output (1 of 1) Enter account number (1 to 100, 0 to end input) ? 37 Enter lastname, firstname, balance ? Barker Doug 0.00 Enter account number ? 29 Enter lastname, firstname, balance ? Brown Nancy Enter account number ? 96 Enter lastname, firstname, balance ? Stone Sam Enter account number ? 88 Enter lastname, firstname, balance ? Smith Dave Enter account number ? 33 Enter lastname, firstname, balance ? Dunn Stacey Enter account number ? 0 Notice that accounts can be created in any order.

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 16 Reading Data Sequentially from a Random-Access File read - similar to write Reads raw bytes from file into memory inFile.read( reinterpret_cast ( &number ), sizeof( int ) ); &number : location to store data sizeof(int) : how many bytes to read Do not use inFile >> number with raw bytes >> expects char * Upcoming program Output data from a random-access file Go through each record sequentially If no data (accountNumber == 0) then skip

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 17 fig14_6.cpp (2 of 3) 26 int main() { 27 ifstream inCredit( "credit.dat", ios::in ); // exit program if ifstream cannot open file 30 if ( !inCredit ) { 31 cerr << "File could not be opened." << endl; 32 exit( 1 ); 33 } // end if 35 cout << left << setw( 10 ) << "Account" << setw( 16 ) 36 << "Last Name" << setw( 11 ) << "First Name" << left 37 << setw( 10 ) << right << "Balance" << endl; 39 ClientData client; // create record // read first record from file 42 inCredit.read( reinterpret_cast ( &client ), 43 sizeof( ClientData ) ); 44

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني // read all records from file 46 while ( inCredit && !inCredit.eof() ) { 47 // display record 48 if ( client.getAccountNumber() != 0 ) 49 outputLine( cout, client ); 51 // read next from file 52 inCredit.read( reinterpret_cast ( &client ), 53 sizeof( ClientData ) ); 54 } // end while 56 return 0; 57 } // end main 59 // display single record 60 void outputLine( ostream &output, const ClientData &record ) { 61 output << left << setw( 10 ) << record.getAccountNumber() 62 << setw( 16 ) << record.getLastName().data() 63 << setw( 11 ) << record.getFirstName().data() 64 << setw( 10 ) << setprecision( 2 ) << right << fixed 65 << showpoint << record.getBalance() << endl; 66 } // end outputLine fig14_6.cpp (3 of 3)

نظام المحاضرات الالكترونينظام المحاضرات الالكتروني 19 fig14_6.cpp output : Account Last Name First Name Balance 29 Brown Nancy Dunn Stacey Barker Doug Smith Dave Stone Sam 34.98