Ngôn ngữ lập trình C++ - Chương 7: Ra vào dữ liệu

 2) 25 // accessor functions for firstName 26 void setFirstName( string ); 27 string getFirstName() const; 28 29 // accessor functions for balance 30 void setBalance( double ); 31 double getBalance() const; 32 33 private: 34 int accountNumber; 35 char lastName[ 15 ]; 36 char firstName[ 10 ]; 37 double balance; 38 39 }; // end class ClientData 40 41 #endif ClientData.cpp(1 of 4) 1 // Fig. 14.11: ClientData.cpp 2 // Class ClientData stores customer's credit information. 3 #include 4 5 using std::string; 6 7 #include 8 #include "clientData.h" 9 10 // default ClientData constructor 11 ClientData::ClientData( int accountNumberValue, 12 string lastNameValue, string firstNameValue, 13 double balanceValue ) 14 { 15 setAccountNumber( accountNumberValue ); 16 setLastName( lastNameValue ); 17 setFirstName( firstNameValue ); 18 setBalance( balanceValue ); 19 20 } // end ClientData constructor 21 22 // get account-number value 23 int ClientData::getAccountNumber() const 24 { 25 return accountNumber; 26 27 } // end function getAccountNumber ClientData.cpp(2 of 4) 28 29 // set account-number value 30 void ClientData::setAccountNumber( int accountNumberValue ) 31 { 32 accountNumber = accountNumberValue; 33 34 } // end function setAccountNumber 35 36 // get last-name value 37 string ClientData::getLastName() const 38 { 39 return lastName; 40 41 } // end function getLastName 42 43 // set last-name value 44 void ClientData::setLastName( string lastNameString ) 45 { 46 // copy at most 15 characters from string to lastName 47 const char *lastNameValue = lastNameString.data(); 48 int length = strlen( lastNameValue ); 49 length = ( length 4 5 using std::cerr; 6 using std::endl; 7 using std::ios; 8 9 #include 10 11 using std::ofstream; 12 13 #include 14 #include "clientData.h" // ClientData class definition 15 16 int main() 17 { 18 ofstream outCredit( "credit.dat", ios::binary ); 19 20 // exit program if ofstream could not open file 21 if ( !outCredit ) { 22 cerr ( &blankClient ), 34 sizeof( ClientData ) ); 35 36 return 0; 37 38 } // end main 7.13.3 Ghi dữ liệu vào vị trí tùy ý trong file truy nhập ngẫu nhiên Dùng seekp để ghi vào vị trí chính xác trong file Bản ghi đầu tiên bắt đầu từ đâu? Byte 0 Bản ghi thứ hai? Byte 0 + sizeof(object) Bản ghi bất kỳ? (Recordnum - 1) * sizeof(object) fig14_13.cpp(1 of 3) 1 // Fig. 14.13: fig14_13.cpp 2 // Writing to a random access file. 3 #include ...... 19 #include 20 #include "clientData.h" // ClientData class definition 21 22 int main() 23 { 24 int accountNumber; 25 char lastName[ 15 ]; 26 char firstName[ 10 ]; 27 double balance; 28 29 ofstream outCredit( "credit.dat", ios::binary ); 30 31 // exit program if ofstream cannot open file 32 if ( !outCredit ) { 33 cerr > accountNumber; 44 client.setAccountNumber( accountNumber ); 45 46 // user enters information, which is copied into file 47 while ( client.getAccountNumber() > 0 && 48 client.getAccountNumber() > setw( 15 ) >> lastName; 53 cin >> setw( 10 ) >> firstName; 54 cin >> balance; 55 56 // set record lastName, firstName and balance values 57 client.setLastName( lastName ); 58 client.setFirstName( firstName ); 59 client.setBalance( balance ); fig14_13.cpp(3 of 3) 60 61 // seek position in file of user-specified record 62 outCredit.seekp( ( client.getAccountNumber() - 1 ) * 63 sizeof( ClientData ) ); 64 65 // write user-specified information in file 66 outCredit.write( 67 reinterpret_cast( &client ), 68 sizeof( ClientData ) ); 69 70 // enable user to specify another account number 71 cout > accountNumber; 73 client.setAccountNumber( accountNumber ); 74 75 } // end while 76 77 return 0; 78 79 } // end main fig14_13.cppoutput (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 -24.54 Enter account number ? 96 Enter lastname, firstname, balance ? Stone Sam 34.98 Enter account number ? 88 Enter lastname, firstname, balance ? Smith Dave 258.34 Enter account number ? 33 Enter lastname, firstname, balance ? Dunn Stacey 314.33 Enter account number ? 0 7.13.4 Đọc tuần tự dữ liệu từ file truy nhập ngẫu nhiên read - tương tự write Đọc các byte thô từ file vào bộ nhớ inFile.read( reinterpret_cast( &number ), 	sizeof( int ) ); &number: địa chỉ để lưu dữ liệu sizeof(int): số byte cần đọc Không dùng inFile >> number cho dữ liệu thô - nhị phân >> nhận char * Chương trình tiếp theo lấy dữ liệu từ một file random-access duyệt tuần tự qua từng bản ghi If no data (accountNumber == 0) then skip fig14_14.cpp(1 of 2) 1 // Fig. 14.14: fig14_14.cpp 2 // Reading a random access file. ...... 25 #include "clientData.h" // ClientData class definition 26 27 void outputLine( ostream&, const ClientData & ); 28 29 int main() 30 { 31 ifstream inCredit( "credit.dat", ios::in ); 32 33 // exit program if ifstream cannot open file 34 if ( !inCredit ) { 35 cerr ( &client ), 48 sizeof( ClientData ) ); fig14_14.cpp(2 of 2) 50 // read all records from file 51 while ( inCredit && !inCredit.eof() ) { 52 53 // display record 54 if ( client.getAccountNumber() != 0 ) 55 outputLine( cout, client ); 56 57 // read next from file 58 inCredit.read( reinterpret_cast( &client ), 59 sizeof( ClientData ) ); 60 61 } // end while 62 63 return 0; 64 65 } // end main 66 67 // display single record 68 void outputLine( ostream &output, const ClientData &record ) 69 { 70 output 6 7 using std::cout; ... 15 using std::showpoint; 16 17 #include 18 19 using std::ofstream; 20 using std::ostream; 21 using std::fstream; 22 23 #include 24 25 using std::setw; 26 using std::setprecision; 27 28 #include // exit prototype 29 #include "clientData.h" // ClientData class definition fig14_15.cpp(2 of 14) 30 31 int enterChoice(); 32 void printRecord( fstream& ); 33 void updateRecord( fstream& ); 34 void newRecord( fstream& ); 35 void deleteRecord( fstream& ); 36 void outputLine( ostream&, const ClientData & ); 37 int getAccount( const char * const ); 38 39 enum Choices { PRINT = 1, UPDATE, NEW, DELETE, END }; 40 41 int main() 42 { 43 // open file for reading and writing 44 fstream inOutCredit( "credit.dat", ios::in | ios::out ); 45 46 // exit program if fstream cannot open file 47 if ( !inOutCredit ) { 48 cerr > menuChoice; // receive choice from user 109 110 return menuChoice; 111 112 } // end function enterChoice 113 114 // create formatted text file for printing 115 void printRecord( fstream &readFromFile ) 116 { 117 // create text file 118 ofstream outPrintFile( "print.txt", ios::out ); 119 120 // exit program if ofstream cannot create file 121 if ( !outPrintFile ) { 122 cerr ( &client ), 137 sizeof( ClientData ) ); 138 139 // copy all records from record file into text file 140 while ( !readFromFile.eof() ) { 141 142 // write single record to text file 143 if ( client.getAccountNumber() != 0 ) 144 outputLine( outPrintFile, client ); 145 146 // read next record from record file 147 readFromFile.read( reinterpret_cast( &client ), 148 sizeof( ClientData ) ); 149 150 } // end while 151 152 } // end function printRecord 153 fig14_15.cpp(8 of 14) 154 // update balance in record 155 void updateRecord( fstream &updateFile ) 156 { 157 // obtain number of account to update 158 int accountNumber = getAccount( "Enter account to update" ); 159 160 // move file-position pointer to correct record in file 161 updateFile.seekg( 162 ( accountNumber - 1 ) * sizeof( ClientData ) ); 163 164 // read first record from file 165 ClientData client; 166 updateFile.read( reinterpret_cast( &client ), 167 sizeof( ClientData ) ); 168 169 // update record 170 if ( client.getAccountNumber() != 0 ) { 171 outputLine( cout, client ); 172 173 // request user to specify transaction 174 cout > transaction; fig14_15.cpp(9 of 14) 177 178 // update record balance 179 double oldBalance = client.getBalance(); 180 client.setBalance( oldBalance + transaction ); 181 outputLine( cout, client ); 182 183 // move file-position pointer to correct record in file 184 updateFile.seekp( 185 ( accountNumber - 1 ) * sizeof( ClientData ) ); 186 187 // write updated record over old record in file 188 updateFile.write( 189 reinterpret_cast( &client ), 190 sizeof( ClientData ) ); 191 192 } // end if 193 194 // display error if account does not exist 195 else 196 cerr ( &client ), 214 sizeof( ClientData ) ); 215 216 // create record, if record does not previously exist 217 if ( client.getAccountNumber() == 0 ) { 218 219 char lastName[ 15 ]; 220 char firstName[ 10 ]; 221 double balance; fig14_15.cpp(11 of 14) 222 223 // user enters last name, first name and balance 224 cout > setw( 15 ) >> lastName; 226 cin >> setw( 10 ) >> firstName; 227 cin >> balance; 228 229 // use values to populate account values 230 client.setLastName( lastName ); 231 client.setFirstName( firstName ); 232 client.setBalance( balance ); 233 client.setAccountNumber( accountNumber ); 234 235 // move file-position pointer to correct record in file 236 insertInFile.seekp( ( accountNumber - 1 ) * 237 sizeof( ClientData ) ); 238 239 // insert record in file 240 insertInFile.write( 241 reinterpret_cast( &client ), 242 sizeof( ClientData ) ); 243 244 } // end if 245 fig14_15.cpp(12 of 14) 246 // display error if account previously exists 247 else 248 cerr ( &client ), 266 sizeof( ClientData ) ); 267 fig14_15.cpp(13 of 14) 268 // delete record, if record exists in file 269 if ( client.getAccountNumber() != 0 ) { 270 ClientData blankClient; 271 272 // move file-position pointer to correct record in file 273 deleteFromFile.seekp( ( accountNumber - 1 ) * 274 sizeof( ClientData ) ); 275 276 // replace existing record with blank record 277 deleteFromFile.write( 278 reinterpret_cast( &blankClient ), 279 sizeof( ClientData ) ); 280 281 cout > accountNumber; 311 312 } while ( accountNumber 100 ); 313 314 return accountNumber; 315 316 } // end function getAccount