Download File Processing - Lecture Slides | CS 350 and more Study notes Computer Science in PDF only on Docsity!
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Chapter 11 – File Processing
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Judy
Judy Green
Sally Black
Tom Blue
Judy Green
Iris Orange
Randy Red
File
Record
Field
Byte (ASCII character J)
Bit
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– FILE myPtr; "!# FILE $&%(')&+-,/.
- myPtr = fopen("myFile.dat", openmode);
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– fprintf p]q r*s9t printfu/v wVx&vhy&z{7| }~zh}N(cv/
Az| ~ FILE
A( V/_7A* 4/ = Ac -/
– feof(FILE pointer) _ 7J &¡ true ¢£(¤/¥&¦¨§© £ª§£ª¢ «¤
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– fclose(FILE pointer) ¼h½ ¾¿ÀÁ ÀÀ Â&Á ½ à Īà Á ÅÆĪÃ*¾ Á
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r Open a file for reading.
w Create a file for writing. If the file already exists, discard the current contents.
a Append; open or create a file for writing at end of file.
r+ Open a file for update (reading and writing).
w+ Create a file for update. If the file already exists, discard the current contents.
a+ Append; open or create a file for update; writing is done at the end of the file.
2000 Prentice Hall, Inc. All rights reserved.
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1 /* Fig. 11.3: fig11_03.c 2 Create a sequential file */ 3 #include <stdio.h> 4 5 int main() 6 { 7 int account; 8 char name[ 30 ]; 9 double balance; 10 FILE cfPtr; / cfPtr = clients.dat file pointer */
11
12 if ( ( cfPtr = fopen( "clients.dat", "w" ) ) == NULL ) 13 printf( "File could not be opened\n" );
14 else {
15 printf( "Enter the account, name, and balance.\n" ); 16 printf( "Enter EOF to end input.\n" );
17 printf( "? " );
18 scanf( "%d%s%lf", &account, name, &balance );
19 20 while ( !feof( stdin ) ) {
21 fprintf( cfPtr, "%d %s %.2f\n",
22 account, name, balance ); 23 printf( "? " );
24 scanf( "%d%s%lf", &account, name, &balance );
25 } 26
27 fclose( cfPtr );
28 } 29
30 return 0;
31 }
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Enter the account, name, and balance. Enter EOF to end input. ? 100 Jones 24. ? 200 Doe 345. ? 300 White 0. ? 400 Stone -42. ? 500 Rich 224. ?
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FILE ! "#%$&
myPtr = fopen( "myFile.dat", "r" );
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fscanf( myPtr, "%d%s%f", &myInt, &myString, &myFloat );
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1 /* Fig. 11.7: fig11_07.c 2 Reading and printing a sequential file */ 3 #include <stdio.h> 4 5 int main() 6 { 7 int account; 8 char name[ 30 ]; 9 double balance; 10 FILE cfPtr; / cfPtr = clients.dat file pointer */ 11 12 if ( ( cfPtr = fopen( "clients.dat", "r" ) ) == NULL ) 13 printf( "File could not be opened\n" ); 14 else { 15 printf( "%-10s%-13s%s\n", "Account", "Name", "Balance" ); 16 fscanf( cfPtr, "%d%s%lf", &account, name, &balance ); 17 18 while ( !feof( cfPtr ) ) { 19 printf( "%-10d%-13s%7.2f\n", account, name, balance ); 20 fscanf( cfPtr, "%d%s%lf", &account, name, &balance ); 21 } 22 23 fclose( cfPtr ); 24 } 25 26 return 0; 27 }
Account Name Balance 100 Jones 24. 200 Doe 345. 300 White 0. 400 Stone -42. 500 Rich 224.
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1 /* Fig. 11.8: fig11_08.c 2 Credit inquiry program */ 3 #include <stdio.h> 4 5 int main() 6 { 7 int request, account; 8 double balance; 9 char name[ 30 ]; 10 FILE *cfPtr;
11 12 if ( ( cfPtr = fopen( "clients.dat", "r" ) ) == NULL )
13 printf( "File could not be opened\n" ); 14 else {
15 printf( "Enter request\n" 16 " 1 - List accounts with zero balances\n"
17 " 2 - List accounts with credit balances\n" 18 " 3 - List accounts with debit balances\n" 19 " 4 - End of run\n? " );
20 scanf( "%d", &request ); 21
22 while ( request != 4 ) { 23 fscanf( cfPtr, "%d%s%lf", &account, name,
24 &balance ); 25 26 switch ( request ) {
27 case 1: 28 printf( "\nAccounts with zero "
29 "balances:\n" ); 30
31 while ( !feof( cfPtr ) ) { 32
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33 if ( balance == 0 )
34 printf( "%-10d%-13s%7.2f\n", 35 account, name, balance );
36 37 fscanf( cfPtr, "%d%s%lf",
38 &account, name, &balance ); 39 } 40
41 break; 42 case 2:
43 printf( "\nAccounts with credit " 44 "balances:\n" );
45 46 while ( !feof( cfPtr ) ) { 47
48 if ( balance < 0 ) 49 printf( "%-10d%-13s%7.2f\n",
50 account, name, balance ); 51
52 fscanf( cfPtr, "%d%s%lf", 53 &account, name, &balance );
54 } 55 56 break;
57 case 3: 58 printf( "\nAccounts with debit "
59 "balances:\n" ); 60
61 while ( !feof( cfPtr ) ) { 62 63 if ( balance > 0 )
64 printf( "%-10d%-13s%7.2f\n",
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300 White 0.00 400 Jones 32.87 (old data in file)
If we want to change White’s name to Worthington,
300 White 0.00 400 Jones 32.
300 Worthington 0.00ones 32.
300 Worthington 0.
Data gets overwritten
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bytes
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1 /* Fig. 11.11: fig11_11.c 2 Creating a randomly accessed file sequentially */ 3 #include <stdio.h> 4 5 struct clientData { 6 int acctNum; 7 char lastName[ 15 ]; 8 char firstName[ 10 ]; 9 double balance;
10 };
11
12 int main()
13 {
14 int i;
15 struct clientData blankClient = { 0, "", "", 0.0 };
16 FILE *cfPtr;
17
18 if ( ( cfPtr = fopen( "credit.dat", "w" ) ) == NULL )
19 printf( "File could not be opened.\n" );
20 else {
21
22 for ( i = 1; i <= 100; i++ )
23 fwrite( &blankClient,
24 sizeof( struct clientData ), 1, cfPtr );
25
26 fclose( cfPtr );
27 }
28
29 return 0;
30 }
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- fseek( myPtr, offset, symbolic_constant);
- myPtr ²2³ ´μ ¶ ·¹¸º&·¹´K»μ ¼¸
- offset ½X¾À¿ ÁÂÄà ÅÆh¿ Ç¿ ÅÈKÃÅ¿ ÈǹÂÉÊÌË*¿ ƾÀ¿ ÉÆÇÁ ÅhÍÎÇ¿ ÅÈhÏ
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- SEEK_SET âXãUä ä åã,æ ç5è£æÌã2çæé äê_ë ì5ìZë ì êîí ïGï0ë ðä
- SEEK_CUR ñXòUó ó ôò,õ ö5÷£õÌò2öõøùZ÷ ÷Ìó5ú õû üZøÀöõ¹ý üZúý ú$þ ýûó
- SEEK_END ÿ
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1 /* Fig. 11.12: fig11_12.c 2 Writing to a random access file */ 3 #include <stdio.h> 4 5 struct clientData { 6 int acctNum; 7 char lastName[ 15 ]; 8 char firstName[ 10 ]; 9 double balance; 10 };
11 12 int main()
13 { 14 FILE *cfPtr;
15 struct clientData client = { 0, "", "", 0.0 }; 16
17 if ( ( cfPtr = fopen( "credit.dat", "r+" ) ) == NULL ) 18 printf( "File could not be opened.\n" ); 19 else {
20 printf( "Enter account number" 21 " ( 1 to 100, 0 to end input )\n? " );
22 scanf( "%d", &client.acctNum ); 23
24 while ( client.acctNum != 0 ) { 25 printf( "Enter lastname, firstname, balance\n? " ); 26 fscanf( stdin, "%s%s%lf", client.lastName,
27 client.firstName, &client.balance ); 28 fseek( cfPtr, ( client.acctNum - 1 ) *
29 sizeof( struct clientData ), SEEK_SET ); 30 fwrite( &client, sizeof( struct clientData ), 1,
31 cfPtr ); 32 printf( "Enter account number\n? " );
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33 scanf( "%d", &client.acctNum );
34 }
35
36 fclose( cfPtr );
37 }
38
39 return 0;
40 }
Enter account number (1 to 100, 0 to end input) ? 37 Enter lastname, firstname, balance ? Barker Doug 0. Enter account number ? 29 Enter lastname, firstname, balance ? Brown Nancy -24. Enter account number ? 96 Enter lastname, firstname, balance ? Stone Sam 34.
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1 /* Fig. 11.15: fig11_15.c 2 Reading a random access file sequentially */ 3 #include <stdio.h> 4 5 struct clientData { 6 int acctNum; 7 char lastName[ 15 ]; 8 char firstName[ 10 ]; 9 double balance; 10 };
11 12 int main()
13 { 14 FILE *cfPtr;
15 struct clientData client = { 0, "", "", 0.0 }; 16
17 if ( ( cfPtr = fopen( "credit.dat", "r" ) ) == NULL ) 18 printf( "File could not be opened.\n" ); 19 else {
20 printf( "%-6s%-16s%-11s%10s\n", "Acct", "Last Name", 21 "First Name", "Balance" );
22 23 while ( !feof( cfPtr ) ) {
24 fread( &client, sizeof( struct clientData ), 1, 25 cfPtr ); 26
27 if ( client.acctNum != 0 ) 28 printf( "%-6d%-16s%-11s%10.2f\n",
29 client.acctNum, client.lastName, 30 client.firstName, client.balance );
31 } 32
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33 fclose( cfPtr );
36 return 0;
37 }
Acct Last Name First Name Balance 29 Brown Nancy -24. 33 Dunn Stacey 314. 37 Barker Doug 0. 88 Smith Dave 258. 96 Stone Sam 34.
2000 Prentice Hall, Inc. All rights reserved.
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2000 Prentice Hall, Inc. All rights reserved.
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1 /* Fig. 11.16: fig11_16.c 2 This program reads a random access file sequentially, 3 updates data already written to the file, creates new 4 data to be placed in the file, and deletes data 5 already in the file. */ 6 #include <stdio.h> 7 8 struct clientData { 9 int acctNum; 10 char lastName[ 15 ];
11 char firstName[ 10 ]; 12 double balance;
13 }; 14 15 int enterChoice( void );
16 void textFile( FILE * ); 17 void updateRecord( FILE * );
18 void newRecord( FILE * ); 19 void deleteRecord( FILE * );
20 21 int main()
22 { 23 FILE *cfPtr; 24 int choice;
25 26 if ( ( cfPtr = fopen( "credit.dat", "r+" ) ) == NULL )
27 printf( "File could not be opened.\n" ); 28 else {
29 30 while ( ( choice = enterChoice() ) != 5 ) { 31
32 switch ( choice ) {
2000 Prentice Hall, Inc. All rights reserved.
FG
H"! S903(32&,/' E&(AB#&% '(3' ,/' E&(3*
97 printf( "%-6d%-16s%-11s%10.2f\n\n",
98 client.acctNum, client.lastName,
99 client.firstName, client.balance );
100 printf( "Enter charge ( + ) or payment ( - ): " );
101 scanf( "%lf", &transaction );
102 client.balance += transaction;
103 printf( "%-6d%-16s%-11s%10.2f\n",
104 client.acctNum, client.lastName,
105 client.firstName, client.balance );
106 fseek( fPtr,
107 ( account - 1 ) * sizeof( struct clientData ),
108 SEEK_SET );
109 fwrite( &client, sizeof( struct clientData ), 1,
110 fPtr );
111 }
112 }
113
114 void deleteRecord( FILE *fPtr )
115 {
116 struct clientData client,
117 blankClient = { 0, "", "", 0 };
118 int accountNum;
119
120 printf( "Enter account number to "
121 "delete ( 1 - 100 ): " );
122 scanf( "%d", &accountNum );
123 fseek( fPtr,
124 ( accountNum - 1 ) * sizeof( struct clientData ),
125 SEEK_SET );
126 fread( &client, sizeof( struct clientData ), 1, fPtr );
2000 Prentice Hall, Inc. All rights reserved.
FG
H"! S903(32&,/' E&(AB#&% '(3' ,/' E&(3*
128 if ( client.acctNum == 0 )
129 printf( "Account %d does not exist.\n", accountNum );
130 else {
131 fseek( fPtr,
132 ( accountNum - 1 ) * sizeof( struct clientData ),
133 SEEK_SET );
134 fwrite( &blankClient,
135 sizeof( struct clientData ), 1, fPtr );
136 }
137 }
138
139 void newRecord( FILE *fPtr )
140 {
141 struct clientData client = { 0, "", "", 0.0 };
142 int accountNum;
143 printf( "Enter new account number ( 1 - 100 ): " );
144 scanf( "%d", &accountNum );
145 fseek( fPtr,
146 ( accountNum - 1 ) * sizeof( struct clientData ),
147 SEEK_SET );
148 fread( &client, sizeof( struct clientData ), 1, fPtr );
149
150 if ( client.acctNum != 0 )
151 printf( "Account #%d already contains information.\n",
152 client.acctNum );
153 else {
154 printf( "Enter lastname, firstname, balance\n? " );
155 scanf( "%s%s%lf", &client.lastName, &client.firstName,
156 &client.balance );
2000 Prentice Hall, Inc. All rights reserved.
FG
H"! S903(32&,/' E&(AB#&% '(3' ,/' E&(3*
157 client.acctNum = accountNum;
158 fseek( fPtr, ( client.acctNum - 1 ) *
159 sizeof( struct clientData ), SEEK_SET );
160 fwrite( &client,
161 sizeof( struct clientData ), 1, fPtr );
162 }
163 }
164
165 int enterChoice( void )
166 {
167 int menuChoice;
168
169 printf( "\nEnter your choice\n"
170 "1 - store a formatted text file of acounts called\n"
171 " "accounts.txt" for printing\n"
172 "2 - update an account\n"
173 "3 - add a new account\n"
174 "4 - delete an account\n"
175 "5 - end program\n? " );
176 scanf( "%d", &menuChoice );
177 return menuChoice;
178 }
2000 Prentice Hall, Inc. All rights reserved.
FG
K.E&L&. 6 &MN>@03,/?03,
Enter account to update (1 - 100): 37 37 Barker Doug 0.
Enter charge (+) or payment (-): +87. 37 Barker Doug 87.
Enter new account number (1 - 100): 22 Enter lastname, firstname, balance ? Johnston Sarah 247.
After choosing option 1 accounts.txt contains:
Acct Last Name First Name Balance 29 Brown Nancy -24. 33 Dunn Stacey 314. 37 Barker Doug 0. 88 Smith Dave 258. 96 Stone Sam 34.
