14.11 Case Study: A Transaction-Processing Program
We now present a substantial transaction-processing program (Fig. 14.13) using a random-access file to achieve instant-access processing. The program maintains a bank’s account information. It updates existing accounts, adds new accounts, deletes accounts and stores a formatted listing of all current accounts in a text file. We assume that the program of Fig. 14.10 has been executed to create the file credit.dat and that the program of Fig. 14.11 has been executed to insert the initial data. Line 25 opens the credit.dat file by creating an fstream object for both reading and writing in binary format.
Fig. 14.13 Bank-account program.
Alternate View
1 // Fig. 14.13: Fig14_13.cpp
2 // This program reads a random-access file sequentially, updates
3 // data previously written to the file, creates data to be placed
4 // in the file, and deletes data previously stored in the file.
5 #include <iostream>
6 #include <fstream>
7 #include <iomanip>
8 #include <cstdlib>
9 #include "ClientData.h" // ClientData class definition
10 using namespace std;
11
12 enum class Choice {PRINT = 1, UPDATE, NEW, DELETE, END};
13
14 Choice enterChoice();
15 void createTextFile(fstream&);
16 void updateRecord(fstream&);
17 void newRecord(fstream&);
18 void deleteRecord(fstream&);
19 void outputLine(ostream&, const ClientData&);
20 int getAccount(const char* const);
21
22 int main() {
23
24 // open file for reading and writing
25 fstream inOutCredit{"credit.dat", ios::in | ios::out | ios::binary};
26
27 // exit program if fstream cannot open file
28 if (!inOutCredit) {
29 cerr << "File could not be opened." << endl;
30 exit (EXIT_FAILURE);
31 }
32
33 Choice choice; // store user choice
34
35 // enable user to specify action
36 while ((choice = enterChoice()) != Choice::END) {
37 switch (choice) {
38 case Choice::PRINT: // create text file from record file
39 createTextFile(inOutCredit);
40 break;
41 case Choice::UPDATE: // update record
42 updateRecord(inOutCredit);
43 break;
44 case Choice::NEW: // create record
45 newRecord(inOutCredit);
46 break;
47 case Choice::DELETE: // delete existing record
48 deleteRecord(inOutCredit);
49 break;
50 default: // display error if user does not select valid choice
51 cerr << "Incorrect choice" << endl;
52 break;
53 }
54
55 inOutCredit.clear(); // reset end-of-file indicator
56 }
57 }
58
59 // enable user to input menu choice
60 Choice enterChoice() {
61 // display available options
62 cout << "
Enter your choice
"
63 << "1 - store a formatted text file of accounts
"
64 << " called "print.txt" for printing
"
65 << "2 - update an account
"
66 << "3 - add a new account
"
67 << "4 - delete an account
"
68 << "5 - end program
? ";
69
70 int menuChoice;
71 cin >> menuChoice; // input menu selection from user
72 return static_cast<Choice>(menuChoice);
73 }
74
75 // create formatted text file for printing
76 void createTextFile(fstream& readFromFile) {
77 ofstream outPrintFile("print.txt", ios::out); // create text file
78
79 // exit program if ofstream cannot create file
80 if (!outPrintFile) {
81 cerr << "File could not be created." << endl;
82 exit(EXIT_FAILURE);
83 }
84
85 // output column heads
86 outPrintFile << left << setw(10) << "Account" << setw(16)
87 << "Last Name" << setw(11) << "First Name" << right
88 << setw(10) << "Balance" << endl;
89
90 // set file-position pointer to beginning of readFromFile
91 readFromFile.seekg(0);
92
93 // read first record from record file
94 ClientData client;
95 readFromFile.read(
96 reinterpret_cast<char*>(&client), sizeof(ClientData));
97
98 // copy all records from record file into text file
99 while (!readFromFile.eof()) {
100 // write single record to text file
101 if (client.getAccountNumber() != 0) { // skip empty records
102 outputLine(outPrintFile, client);
103 }
104
105 // read next record from record file
106 readFromFile.read(
107 reinterpret_cast<char*>(&client), sizeof(ClientData));
108 }
109 }
110
111 // update balance in record
112 void updateRecord(fstream& updateFile) {
113 // obtain number of account to update
114 int accountNumber{getAccount("Enter account to update")};
115
116 // move file-position pointer to correct record in file
117 updateFile.seekg((accountNumber - 1) * sizeof(ClientData));
118
119 // create record object and read first record from file
120 ClientData client;
121 updateFile.read(reinterpret_cast<char*>(&client), sizeof(ClientData));
122
123 // update record
124 if (client.getAccountNumber() != 0) {
125 outputLine(cout, client); // display the record
126
127 // request user to specify transaction
128 cout << "
Enter charge (+) or payment (-): ";
129 double transaction; // charge or payment
130 cin >> transaction;
131
132 // update record balance
133 double oldBalance = client.getBalance();
134 client.setBalance(oldBalance + transaction);
135 outputLine(cout, client); // display the record
136
137 // move file-position pointer to correct record in file
138 updateFile.seekp((accountNumber - 1) * sizeof(ClientData));
139
140 // write updated record over old record in file
141 updateFile.write(
142 reinterpret_cast<const char*>(&client), sizeof(ClientData));
143 }
144 else { // display error if account does not exist
145 cerr << "Account #" << accountNumber
146 << " has no information." << endl;
147 }
148 }
149
150 // create and insert record
151 void newRecord(fstream& insertInFile) {
152 // obtain number of account to create
153 int accountNumber{getAccount("Enter new account number")};
154
155 // move file-position pointer to correct record in file
156 insertInFile.seekg((accountNumber - 1) * sizeof(ClientData));
157
158 // read record from file
159 ClientData client;
160 insertInFile.read(
161 reinterpret_cast<char*>(&client), sizeof(ClientData));
162
163 // create record, if record does not previously exist
164 if (client.getAccountNumber() == 0) {
165 string lastName;
166 string firstName;
167 double balance;
168
169 // user enters last name, first name and balance
170 cout << "Enter lastname, firstname, balance
? ";
171 cin >> setw(15) >> lastName;
172 cin >> setw(10) >> firstName;
173 cin >> balance;
174
175 // use values to populate account values
176 client.setLastName(lastName);
177 client.setFirstName(firstName);
178 client.setBalance(balance);
179 client.setAccountNumber(accountNumber);
180
181 // move file-position pointer to correct record in file
182 insertInFile.seekp((accountNumber - 1) * sizeof(ClientData));
183
184 // insert record in file
185 insertInFile.write(
186 reinterpret_cast<const char*>(&client), sizeof(ClientData));
187 }
188 else { // display error if account already exists
189 cerr << "Account #" << accountNumber
190 << " already contains information." << endl;
191 }
192 }
193
194 // delete an existing record
195 void deleteRecord(fstream& deleteFromFile) {
196 // obtain number of account to delete
197 int accountNumber{getAccount("Enter account to delete")};
198
199 // move file-position pointer to correct record in file
200 deleteFromFile.seekp((accountNumber - 1) * sizeof(ClientData));
201
202 // read record from file
203 ClientData client;
204 deleteFromFile.read(
205 reinterpret_cast<char*>(&client), sizeof(ClientData));
206
207 // delete record, if record exists in file
208 if (client.getAccountNumber() != 0) {
209 ClientData blankClient; // create blank record
210
211 // move file-position pointer to correct record in file
212 deleteFromFile.seekg((accountNumber - 1) * sizeof(ClientData));
213
214 // replace existing record with blank record
215 deleteFromFile.write(
216 reinterpret_cast<const char*>(&blankClient), sizeof(ClientData));
217
218 cout << "Account #" << accountNumber << " deleted.
";
219 }
220 else { // display error if record does not exist
221 cerr << "Account #" << accountNumber << " is empty.
";
222 }
223 }
224
225 // display single record
226 void outputLine(ostream& output, const ClientData& record) {
227 output << left << setw(10) << record.getAccountNumber()
228 << setw(16) << record.getLastName()
229 << setw(11) << record.getFirstName()
230 << setw(10) << setprecision(2) << right << fixed
231 << showpoint << record.getBalance() << endl;
232 }
233
234 // obtain account-number value from user
235 int getAccount(const char* const prompt) {
236 int accountNumber;
237
238 // obtain account-number value
239 do {
240 cout << prompt << " (1 - 100): ";
241 cin >> accountNumber;
242 } while (accountNumber < 1 || accountNumber > 100);
243
244 return accountNumber;
245 }
The program has five options (Option 5 is for terminating the program). Option 1 calls function createTextFile to store a formatted list of all the account information in a text file called print.txt that may be printed. Function createTextFile (lines 76–109) takes an fstream object as an argument to be used to input data from the credit.dat file. Function createTextFile invokes istream member function read (lines 95–96) and uses the sequential-file-access techniques of Fig. 14.12 to input data from credit.dat. Function outputLine, discussed in Section 14.10, outputs the data to file print.txt. Note that function createTextFile uses istream member function seekg (line 91) to ensure that the file-position pointer is at the beginning of the file before reading the file’s contents. After choosing Option 1, the print.txt file contains
Account Last Name First Name Balance
29 Brown Nancy -24.54
33 Dunn Stacey 314.33
37 Barker Doug 0.00
88 Smith Dave 258.34
96 Stone Sam 34.98
Option 2 calls updateRecord (lines 112–148) to update an account. This function updates only an existing record, so the function first determines whether the specified record is empty—we use function getAccount (lines 235–245) to read from the user the number of the record to update. Line 121 reads data into object client, using istream member function read. Then line 124 compares the value returned by getAccountNumber of the client object to zero to determine whether the record contains information. If this value is zero, lines 145–146 print an error message indicating that the record is empty. If the record contains information, line 125 displays the record, using function outputLine, line 130 inputs the transaction amount and lines 133–142 calculate the new balance and rewrite the record to the file. A typical execution for Option 2 is
Enter account to update (1 - 100): 37
37 Barker Doug 0.00
Enter charge (+) or payment (-): +87.99
37 Barker Doug 87.99
Option 3 calls function newRecord (lines 151–192) to add a new account to the file. If the user enters an account number for an existing account, newRecord displays an error message indicating that the account exists (lines 189–190). This function adds a new account in the same manner as the program of Fig. 14.11. A typical execution for Option 3 is
Enter new account number (1 - 100): 22
Enter lastname, firstname, balance
? Johnston Sarah 247.45
Option 4 calls function deleteRecord (lines 195–223) to delete a record from the file. Line 197 prompts the user to enter the account number. Only an existing record may be deleted, so, if the specified account is empty, line 221 displays an error message. If the account exists, lines 209–216 reinitialize that account by writing an empty record (blank-Client) to the file. Line 218 displays a message to inform the user that the record has been deleted. A typical execution for Option 4 is
Enter account to delete (1 - 100): 29
Account #29 deleted.