1. Chapter 11
Files
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2. Introduction of File Data files
Can be created, updated, and processed by C programs
Are used for permanent storage of large amounts of data
Storage of data in variables and arrays is only temporary
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3. Input/Output Files: Review and Further Study
Text file: a named collection of characters saved in secondary storage (e.g. on a disk).
To mark the end of a text file: a special end-of-file character. <eof>
Pressing the <return> or <enter> key causes the newline character to be placed in the file. (‘\n’).
This is a text file!<newline>
It has two lines.<newline><eof>
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4. Comparison of I/O with Standard Files and I/O with User-Defined File Pointers
Line
Functions That Access stdin and stdout
Functions That Can Access Any Text File 1
scanf(“%d”, &num);
fscanf(infile,“%d”, &num); 2
printf(“Number=%d\n”,num);
fprintf(outfile, “Number=%d\n”,num);

5. Files and Streams C views each file as a sequence of bytes
File ends with the end-of-file marker
Or, file ends at a specified byte
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6. Creating a Sequential Access File
Creating a File
FILE *cfPtr;
Creates a FILE pointer called cfPtr
cfPtr = fopen(“clients.dat", “w”);
Function fopen returns a FILE pointer to file specified
Takes two arguments – file to open and file open mode
If open fails, NULL returned
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7. Creating a Sequential Access File
fprintf
Used to print to a file
Like printf, except first argument is a FILE pointer (pointer to the file you want to print in)
feof( FILE pointer )
Returns true if end-of-file indicator (no more data to process) is set for the specified file
fclose( FILE pointer )
Closes specified file
Performed automatically when program ends
Good practice to close files explicitly
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8. Creating a Sequential Access File
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9. Creating a Sequential Access File (Ex1)
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10. Creating a Sequential Access File (Ex1)
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11. Program Output Enter the account, name, and balance.
Enter EOF to end input.
? 100 Jones 24.98
? 200 Doe
? 300 White 0.00
? 400 Stone
? 500 Rich
? ^Z
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12. Creating a Sequential Access File (Ex2) using fprintf
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13. ONSATIR.TXT File Bu bir ornek satirdir. Satir no: 1
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14. Creating a Sequential Access File (Ex2) writing char by char using fputc
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15. Reading Data from a Sequential Access File
Reading a sequential access file
Create a FILE pointer, link it to the file to read
cfPtr = fopen( “clients.dat", "r" );
Use fscanf to read from the file
Like scanf, except first argument is a FILE pointer
fscanf( cfPtr, "%d%s%f", &accounnt, name, &balance );
Data read from beginning to end
rewind( cfPtr )
Repositions file position pointer to beginning of file (byte 0)
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16. Sequential-access File
Operating Systems, 2012, Danny Hendler & Roie Zivan

17. Notes on fscanf() Reading in a string: fscanf(cfPtr, “%s”, string)
Reads only a "word" at a time.
Words are separated by a white-space: (space, tab, newline, or any combination of these)
Moves to the next word in the stream automatically after each read.

18. Notes of fgets() Both read data from file, However:
fgets() reads to a newline sign. 
fscanf() only reads up to whitespace.

19. chap8

20. Account Name Balance
Jones
Doe
White
Stone
Rich
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21. Example: Reading all numbers from a file and then prints
their average onto the screen

22. Reading Data from a Sequential Access File
Cannot be modified without the risk of destroying other data
Fields can vary in size
Different representation in files and screen than internal representation
1, 34, -890 are all ints, but have different sizes on disk
300 White Jones (old data in file)
If we want to change White's name to Worthington,
300 White Jones 32.87
300 Worthington 0.00ones 32.87
Data gets overwritten

23. 1. Initialize variables 2. Open file 2.1 Input choice 2.2 Scan files
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.txt", "r" ) ) == NULL )
printf( "File could not be opened\n" );
14 else {
printf( "Enter request\n"
" 1 - List accounts with zero balances\n"
" 2 - List accounts with credit balances\n"
" 3 - List accounts with debit balances\n"
" 4 - End of run\n? " );
scanf( "%d", &request ); 21
while ( request != 4 ) {
fscanf( cfPtr, "%d%s%lf", &account, name,
&balance ); 25
switch ( request ) {
case 1:
printf( "\nAccounts with zero "
"balances:\n" ); 30
while ( !feof( cfPtr ) ) { 32
1. Initialize variables
2. Open file
2.1 Input choice
2.2 Scan files
3. Print

24. 2.2 Scan files 3. Print 33 if ( balance == 0 )
printf( "%-10d%-13s%7.2f\n",
account, name, balance ); 36
fscanf( cfPtr, "%d%s%lf",
&account, name, &balance ); } 40
break;
case 2:
printf( "\nAccounts with credit "
"balances:\n" ); 45
while ( !feof( cfPtr ) ) { 47
if ( balance < 0 )
printf( "%-10d%-13s%7.2f\n",
account, name, balance ); 51
fscanf( cfPtr, "%d%s%lf",
&account, name, &balance ); } 55
break;
case 3:
printf( "\nAccounts with debit "
"balances:\n" ); 60
while ( !feof( cfPtr ) ) { 62
if ( balance > 0 )
printf( "%-10d%-13s%7.2f\n",
2.2 Scan files
3. Print

25. 3.1 Close file 65 account, name, balance ); 66
fscanf( cfPtr, "%d%s%lf",
&account, name, &balance ); } 70
break; } 73
rewind( cfPtr );
printf( "\n? " );
scanf( "%d", &request ); } 78
printf( "End of run.\n" );
fclose( cfPtr );
81 } 82
83 return 0;
84 }
3.1 Close file

26. Program Output Enter request 1 - List accounts with zero balances
Enter request
1 - List accounts with zero balances
2 - List accounts with credit balances
3 - List accounts with debit balances
4 - End of run
? 1
Accounts with zero balances:
White
? 2
Accounts with credit balances:
Stone
? 3
Accounts with debit balances:
Jones
Doe
Rich
? 4
End of run.
Program Output