文件处理

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  文件打开方式            说明
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  ios::app              将所有输出写入文件末尾
  ios::ate              打开文件以便输出，井移到文件末尾(通常用于添加数据)数据可以写入
                            文件中的任何地方
  ios::in               打开文件以便输入
  ios::out              打开文件以便输出
  ios::trunc            删除文件现有内容(是ios::out的默认操作)
  ios::nocreate         如果文件不存在，则文件打开失败
  ios::noreplace        如果文件存在，则文件打开失败
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#ifndef CLNTDATA_H
5 #define CLNTDATA_H
6
7 struct clientData {
8   int accountNumber;
9   char lastName[15];
10   char firstName[10];
11   float balance;
12 } ;
13
14 #endif


6 #include
7 #include
8 #include
9 #include
10 #include "clntdata.h"
11
12 int enterChoice();
13 void textFile( fstream& );
14 void updateRecord( fstream& );
15 void newRecord( fstream& );
16 void deleteRecord( fstream& );
17 void outputLine( ostream&, const clientData & );
18 int getAccount( const char * );
19
20 enum Choices { TEXTFILE = 1, UPDATE, NEW, DELETE, END } ;
21
22 int main()
23 {
24   fstream inOutCredit( "credit.dat", ios::in | ios::out );
25
26   if ( !inOutCredit ) {
27     cerr << "File could not be opened." << endl;
28     exit ( 1 );
29   }
3O
31   int choice;
32
33 while ( ( choice = enetrChoice() ) != END){
34
35     switch ( choice ) {
36       case TEXTFILE:
37          textFile( inOutCredit );
38          break;
39       case UPDATE:
40          updateReeord( inOutCredit );
41          break;
42       case NEW:
43          newRecord( inOutCredit );
44          break;
45       case DELETE:
46          deleteRecord( inOutCredit );
47          break;
48       default:
49          cerr << "Incorrect cholce\n";
50          break;
51     }
52
53     inOutCredit.clear();  // resets end-of-file indicator
54     }
55
56   return 0;
57 }
58
59 // Prompt for and input menu choice
60 int enterChoice()
61 {
62     cout << "\nEnter your choice" << endl
63          << "i - store a formatted text file of accounts\n"
64          << "   called \"print.txt\" for printing\n"
65          << "2 - update an account\n"
66          << "3 - add a new account\n"
67          << "4 - delete an account\n"
68          << "5 - end program\n? ";
69
70     int menuChoice;
71     cin >> menuChoice;
72     return menuChoice;
73 }
74
75 // Create formatted text file for printing
76 void textFile( fstream &readFromFile )
77 {
78   ofstream outPrintFile( "print.txt", ios::out );
79
80   if ( !outPrintFile ) {
81     cerr << "File could not be opened." << endl;
82     exit( 1 );
83     }
84
85   outPrintFile << setiosflags( ios::left ) << setw( 10 )
86      << "Account" << setw( 16 ) << "Last Name" << setw( 11 )
87      << "First Name" << resetiosflags( ios::left )
88      << setw( 10 ) << "Balance" << endl;
89   readFromFile.seekg(0);
90
91   clientData client;
92   readFromFile.read( reinterpret_cast( &client ),
93                                        sizeof( clientData ) );
94
95   while (!readFromFile.eof() ) {
96     if ( client.accountNumber != O )
97        outputLine( outPrintFile, client );
98
99     readFromFile.read( reinterpret_cast( &client ),
100                     sizeof( clientData ) );
1O1   }
102 }
103
104 // Update an account's balance
105 void updateRecord( fstream &updateFile )
106 {
107   int account = getAccount( "Enter account to update" );
108
109   updateFile.seekg( ( account - I ) * sizeof( clientData ) );
110
111   clientData client;
112   updateFile.read( reinterpret_cast( &client ),
113                 sizeof( clientData ) );
114
115   if ( client.accountNumber != 0 ) {
116     outputLine( cout, client );
117     cout << "\nEnter charge (+) or payment (-): ";
118
119     float transaction;   // charge or payment
120     cin >> transaction;  // should validate
121     client.balance += transaction;
122     outputLine( cout, client );
123     updateFile.seekp((account-1) * sizeof(clientData));
124     updateFile.write(
125        reinterpret cast( &client ),
126        sizeof( clientData ) );
127   }
128    else
129      cerr << "Account #" << account
130           << " has no information." << endl;
131 }
132
133 // Create and insert new record
134 void newRecord( fstream &insertInFile )
135 {
136   int account = getAccount( "Enter new account number" );
137
138   insertInFile.seekg( ( account-1 ) * sizeof( clientData  );
139
14O   clientData client;
141   insertInFile.read( reinterpret cast( &client ),
142                  sizeof( clientData ) );
143
144    if ( client.accountNumber == 0 ) {
145       cout << "Enter lastname, firstname, balance\n? ";
146       cin >> client.lastName >> client.firstName
147                              >> client.balance;
148       client.accountNumber = account;
149       insertInFile.seekp( ( account - 1) *
150                             sizeof( clientData ) );
151       insertInFile.write(
152                             reinterpret_cast( &client ),
153                             sizeof( clientData ) );
154    }
155    else
156       cerr << "Account #" << account
157            << " already contains information." << endl;
158 }
159
160 // Delete an existing record        
161 void deleteRecord( fstream &deleteFromFile )
162 {
163   int account = getAccount( "Enter account to delete" );
164
165   deleteFromFile.seekg((account-1) * sizeof( clientData ) );
166
167   clientData client;
168   deleteFromFile.read( reinterpret_cast &client ),
169                    sizeof( clientData ) );
170
171   if ( client.accountNumber != 0 ) {
172     clientData blankClient = { 0, "", "", 0.0 };
173
174     deleteFromFile.seekp( ( account - 1) *
175                       sizeof( clientData ) );
176     deleteFromFile.write(
177        reinterpret cast( &blankClient ),
178        sizeof( clientData ) );
179     cout << "Account #" << account << " deleted." << endl;
180   }
181   else
182     cerr << "Account #" << account << " is empty." << endl;
183 }
184
185 // output a line of client infomation
186 void outputLine( ostream &output, const clientData &c )
187 {
188   output << setiosflags( ios::left ) << setw( 10 )
189          << c.accountNumber << setw( 16 ) << c.lastName
190          << setw( 11 } << c.firstNeme << setw( 10 )
191          << setprecision( 2 ) << resetiosflags( ios::left )
192          << setiosflags( ios::fixed | ios::showpoint )
193          << c.balance << '\n';
194 }
195
196 // Get an account number from the keyboard
197 int getAccount( const char *prompt )
198 {
199   int account;
2OO
201   do {
202     cout << prompt << " (1 - 1oo): ";
203     cin >> account;
204   } while ( account < 1 || account > 100 );
2O5
206   return account;
207 }