1. CSC 211 Data Structures Lecture 32
Dr. Iftikhar Azim Niaz 1

2. Last Lecture Summary Hash Function Properties of a Good Hash Function
Hash Function Methods
File
Text and Binary Files
Operations on Files
File Access Methods
Sequential Files
Indexed Files
Hashed Files 2

3. Objectives Overview File Implementation in C Language
Basic File Operations
Opening a file
Reading data from a file
Writing data to a file
Closing a file
File operations on Text Files
File operations on Sequential Binary Files
Revision of the Course
Lecture 1 to Lecture 31

4. Files - Implementation
Files are places where data can be stored permanently.
Some programs expect the same set of data to be fed as input every time it is run.
Cumbersome.
Better if the data are kept in a file, and the program reads from the file.
Programs generating large volumes of output.
Difficult to view on the screen.
Better to store them in a file for later viewing/ processing 4

5. Text Data Files
When you use a file to store data for use by a program, that file usually consists of text (alphanumeric data) and is therefore called a text file.
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

6. Basic Files Operations
Opening a file
Reading data from a file
Writing data to a file
Closing a file

7. Opening a File A file must be “opened” before it can be used.
FILE *fp; :
fp = fopen (filename, mode);
fp is declared as a pointer to the data type FILE.
filename is a string - specifies the name of the file.
fopen returns a pointer to the file which is used in all subsequent file operations.
mode is a string which specifies the purpose of opening the file:
“r” :: open the file for reading only
“w” :: open the file for writing only
“a” :: open the file for appending data to it

8. File Modes
r - open a file in read-mode, set the pointer to the beginning of the file.
w - open a file in write-mode, set the pointer to the beginning of the file.
a - open a file in write-mode, set the pointer to the end of the file.
rb - open a binary-file in read-mode, set the pointer to beginning of file.
wb - open a binary-file in write-mode, set the pointer to beginning of file.
ab - open a binary-file in write-mode, set the pointer to the end of the file.
r+ - open a file in read/write-mode, if file does not exist, it will not be created.
w+ - open a file in read/write-mode, set the pointer to the beginning of file.
a+ - open a file in read/append mode.
r+b - open a binary-file in read/write-mode, if the file does not exist, it will not be created.
w+b - open a binary-file in read/write-mode, set pointer to beginning of file.
a+b - open a binary-file in read/append mode.

9. File Modes Points to note:
Several files may be opened at the same time.
For the “w” and “a” modes, if the named file does not exist, it is automatically created.
For the “w” mode, if the named file exists, its contents will be overwritten.

10. Opening a File in = fopen (“mydata.dat”, “r”) ;
FILE *in, *out ;
in = fopen (“mydata.dat”, “r”) ;
out = fopen (“result.dat”, “w”);
FILE *empl ;
char filename[25];
scanf (“%s”, filename);
empl = fopen (filename, “r”) ;

11. Closing a File
After all operations on a file have been completed, it must be closed.
Ensures that all file data stored in memory buffers are properly written to the file.
General format: fclose (file_pointer) ;
FILE *xyz ;
xyz = fopen (“test.txt”, “w”) ;
…….
fclose (xyz) ;

12. Closing a File fclose( FILE pointer ) feof( FILE pointer )
Closes specified file
Performed automatically when program ends
Good practice to close files explicitly
system resources are freed.
Also, you might not find that all the information that you've written to the file has actually been written to disk until the file is closed.
feof( FILE pointer )
Returns true if end-of-file indicator (no more data to process) is set for the specified file

13. Read/Write Operations on Text Files
The simplest file input-output (I/O) function are getc and putc.
getc is used to read a character from a file and return it.
char ch; FILE *fp;
ch = getc (fp) ;
getc will return an end-of-file marker EOF, when the end of the file has been reached.
putc is used to write a character to a file.
putc (ch, fp) ;

14. Text File - Example Convert a text file to all UPPERCASE main() {
FILE *in, *out ;
char c ;
in = fopen (“infile.dat”, “r”) ;
out = fopen (“outfile.dat”, “w”) ;
while ((c = getc (in)) != EOF)
putc (toupper (c), out);
fclose (in) ;
fclose (out) ; }

15. Read/Write Operations on Text Files
We can also use the file versions of scanf and printf, called fscanf and fprintf.
General format:
fscanf (file_pointer, control_string, list) ;
fprintf (file_pointer, control_string, list) ;
Examples:
fscanf (fp, “%d %s %f”, &roll, dept_code, &cgpa) ;
fprintf (out, “\nThe result is: %d”, xyz) ;
fprintf
Used to print to a file
It is like printf, except first argument is a FILE pointer (pointer to the file you want to print in)

16. Some Points How to check EOF condition when using fscanf?
Use the function feof
if (feof (fp))
printf (“\n Reached end of file”) ;
How to check successful open?
For opening in “r” mode, the file must exist.
if (fp == NULL)
printf (“\n Unable to open file”) ;

17. Example : Merge Two Text Files
#include <stdio.h>
int main()
{ FILE *fileA, /* first input file */
*fileB, /* second input file */
*fileC; /* output file to be created */
int num1, /* number to be read from first file */
num2; /* number to be read from second file*/
int f1, f2;
/* Open files for processing */
fileA = fopen("class1.txt","r");
fileB = fopen("class2.txt","r");
fileC = fopen("class.txt","w");

18. Example : Merge Two Files
/* As long as there are numbers in both files, read and compare numbersone by one. Write the smaller number to the output file and read the next number in the file from which the smaller number is read. */ f1 = fscanf(fileA, "%d", &num1); f2 = fscanf(fileB, "%d", &num2); while ((f1!=EOF) && (f2!=EOF)){ if (num1 < num2){ fprintf(fileC,"%d\n", num1); f1 = fscanf(fileA, "%d", &num1); } else if (num2 < num1) { fprintf(fileC,"%d\n", num2); f2 = fscanf(fileB, "%d", &num2); } else { /* numbs are equal:read from both files */ fprintf(fileC,"%d\n", num1); f1 = fscanf(fileA, "%d", &num1); f2 = fscanf(fileB, "%d", &num2); } }

19. Example : Merge Two Files
/* if reached end of second file, read the remaining numbers
from first file and write to output file */
while (f1!=EOF){ fprintf(fileC,"%d\n", num1); f1 = fscanf(fileA, "%d", &num1); }
/* if reached the end of first file, read the remaining numbers
from second file and write to output file */ while (f2!=EOF){ fprintf(fileC,"%d\n", num2); f2 = fscanf(fileB, "%d", &num2); } /* close files */ fclose(fileA); fclose(fileB); fclose(fileC); return 0; } /* end of main */

20. Files and Streams FILE structure
C views each file as a sequence of bytes
File ends with the end-of-file marker
Stream created when a file is opened
Provide communication channel between files and programs
Opening a file returns a pointer to a FILE structure
Example file pointers:
stdin - standard input (keyboard)
stdout - standard output (screen)
stderr - standard error (screen)
FILE structure
File descriptor
Index into operating system array called the open file table
File Control Block (FCB)
Found in every array element, system uses it to administer the file

21. Files and Streams Read/Write functions in standard library
fgetc Reads one character from a file
Takes a FILE pointer as an argument
fgetc( stdin ) equivalent to getchar()
fputc Writes one character to a file
Takes a FILE pointer and a character to write as an argument
fputc( 'a', stdout ) equivalent to putchar( 'a' )
fgets reads a line (string) from a file
fputs writes a line (string) to a file
fscanf / fprintf
File processing equivalents of scanf and printf

22. Creating a Sequential Access File
C imposes no file structure
No notion of records in a file
Programmer must provide file structure
Creating a File
FILE *myPtr;
Creates a FILE pointer called myPtr
myPtr = fopen("myFile.dat", openmode);
Function fopen returns a FILE pointer to file specified
Takes two arguments – file to open and file open mode
If open fails, NULL returned
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)

23. Creating a Sequential Access File
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
Details
Programs may process no files, one file, or many files
Each file must have a unique name and should have its own pointer

24. 1. Initialize variables and FILE pointer
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 )
printf( "File could not be opened\n" );
14 else {
printf( "Enter the account, name, and balance.\n" );
printf( "Enter EOF to end input.\n" );
printf( "? " );
scanf( "%d%s%lf", &account, name, &balance ); 19
while ( !feof( stdin ) ) {
fprintf( cfPtr, "%d %s %.2f\n",
account, name, balance );
printf( "? " );
scanf( "%d%s%lf", &account, name, &balance ); } 26
fclose( cfPtr );
28 } 29
30 return 0;
31 }
1. Initialize variables and FILE pointer
1.1 Link the pointer to a file
2. Input data
2.1 Write to file (fprintf)
3. Close file

25. 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 ?
Program Output

26. Reading Data from a Sequential Access File
Reading a sequential access file
Create a FILE pointer, link it to the file to read
myPtr = fopen( "myFile.dat", "r" );
Use fscanf to read from the file
Like scanf, except first argument is a FILE pointer
fscanf( myPtr, "%d%s%f", &myInt, &myString, &myFloat );
Data read from beginning to end
File position pointer
Indicates number of next byte to be read / written
Not really a pointer, but an integer value (specifies byte location)
Also called byte offset
rewind( myPtr )
Repositions file position pointer to beginning of file (byte 0)

27. 1. Initialize variables 1.1 Link pointer to file 2. Read data (fscanf)
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 )
printf( "File could not be opened\n" );
14 else {
printf( "%-10s%-13s%s\n", "Account", "Name", "Balance" );
fscanf( cfPtr, "%d%s%lf", &account, name, &balance ); 17
while ( !feof( cfPtr ) ) {
printf( "%-10d%-13s%7.2f\n", account, name, balance );
fscanf( cfPtr, "%d%s%lf", &account, name, &balance ); } 22
fclose( cfPtr );
24 } 25
26 return 0;
27 }
1. Initialize variables
1.1 Link pointer to file
2. Read data (fscanf)
2.1 Print
3. Close file
Program Output
Account Name Balance
Jones
Doe
White
Stone
Rich

28. 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.dat", "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

29. 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

30. 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

31. 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

32. 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
300 Worthington 0.00
Data gets overwritten

33. Read and Write for Binary Files
size_t fread(void *buffer, size_t numbytes, size_t count, FILE *a_file);
size_t fwrite(void *buffer, size_t numbytes, size_t count, FILE *a_file);
Buffer in fread is a pointer to a region of memory that will receive the data from the file. Buffer in fwrite() is a pointer to the information that will be written to the file.
The second argument is the size of the element; it is in bytes.
Size_t is an unsigned integer.
For example, if you have an array of characters, you would want to read it in one byte chunks, so numbytes is one. You can use the sizeof operator to get the size of the various datatypes; for example, if you have a variable, int x; you can get the size of x with sizeof(x);

34. Read and Write for Binary Files
The third argument count is simply how many elements you want to read or write; for example, if you pass a 100 element array
The final argument is simply the file pointer
fread() returns number of items read and
fwrite() returns number of items written
To check to ensure the end of file was reached, use the feof function, which accepts a FILE pointer and returns true if the end of the file has been reached.

35. Sample Program - 1
/* a simple example of using fread and fwrite to read and write an array of structures */
#include <stdio.h>
#include <conio.h>
int main() {
FILE *fp; // File pointer
struct prod { // declaring record
int cat_num;
float cost; };
typedef struct prod product; // type definition
product a[3] = {{2,20.1},{4,40.1},{6,60.1}};// array of records
product k, *p = &k;

36. Sample Program - 2
// opening the text file in read/write mode
fp = fopen("c:\fread1.dat","w+b");
// write the entire array into the file pointed to by fp
fwrite(a, sizeof(product), 3, fp);
// prepare for reading from the beginning of the file
rewind(fp);
// read from the file one product at a time
for (i=0; i<3; i++) {
fread(p, sizeof(product), 1, fp);
printf(" product %d, cat_num=%d, cost=%f\n",
i, p->cat_num, p->cost);
} // end of for loop
getch();
} // end of main program

37. Revision – Lectures 1 – 4 1 2 3 4 Lecture Topics
Course Outline, Programming and problem solving, Software development method, Program control structures, Algorithm, Pseudocode and Flow chart 2
System Development Life cycle and its phases,
Program Development Life cycle and its phases 3
Generation of programming languages, Compiler Interpreter, Procedural and modular programming
Structure of a C Program, Data and data structure, Abstract Data Type (ADT) 4
Data types in C Language, Arrays, Declaration, operations, Array and functions, Pointers, Arrays and pointers

38. Revision – Lectures 5 – 8 5 6 7 8 Lecture Topics
Concept of Pointer, Pointer operators, Address and Indirection, Pointer Arithmetic, Pointer and functions
Pass by Value, Pass by Reference 6
Dynamic Memory Management with Pointers, Structures, Unions, Strings, Multidimensional Arrays 7
Need for Data Structures, Selecting a data structure
Data structure philosophy, Classification, Common Operations, Arrays and Lists, List Operations 8
Algorithm Analysis, Time and Space Complexity,
Complexity of Algorithms, Measuring Efficiency
Big O Notation, Standard Analysis Techniques

39. Revision – Lecture 9 – 12 9 10 11 12 Lecture Topics
Algorithms and Complexity, Criteria for Algorithm Analysis, Complexity Analysis, Various Complexity Functions, Properties of Big O Notation 10
Data structure Operations, Array-based and Pointer based List ADT, Linked List, Linked List Operations 11
Dynamic Representation, Allocation from Dynamic Storage, Returning unused storage back to dynamic storage, Linked List insert and delete Operations 12
Cursor-based Implementation of List, Search Operation, Sequential Search, Concept, Algorithm and Implementation, Complexity of Sequential Search

40. Revision – Lectures 13 – 16 13 14 15 16 Lecture Topics
Binary Search, Concept, Algorithm and implementation, Binary search complexity, Searching Unordered and Ordered Linked Lists 14
Sorting, Concept, Terminology, Classification, Stability of Key, Bubble Sort, Concept, Algorithm and implementation 15
Bubble Sort Complexity, Selection Sort, Concept, Algorithm, Implementation, Complexity, Insertion Sort, Concept, Algorithm, Implementation, Complexity 16
Comparison of Bubble, Selection and Insertion Sort, Recursion, Concept, Example and Implementation

41. Revision – Lectures 17 – 20 17 18 19 20 Lecture Topics
Recursive Search Algorithms, Recursion with Linked Lists, Recursion and Iteration, Analysis of Recursion 18
Merge Sort, Concept, Algorithm and Implementation
Complexity of Merge Sort 19
Quick Sort, Concept, Algorithm and Implementation
Complexity of Quick Sort 20
Comparison of Merge and Quick Sort, Shell Sort, Radix sort, Bucket Sort, Sorting techniques comparison

42. Revision – Lectures 21 – 24 21 22 23 24 Lecture Topics
Doubly Linked List, Operations, Algorithm and Implementation Code, Doubly Linked List with Two Pointers 22
Queues, Operations, Algorithm and Implementation,
Circular Queue and Deque operations 23
Stacks, Operations, Algorithm and Implementation,
Stack Applications 24
Trees, Concept, Examples and Applications, Tree
Terminology, Types of Trees, General Trees, Representation and Traversal, Binary Tree

43. Revision – Lectures 25 – 28 25 26 27 28 Lecture Topics
Binary Tree Operations and Traversal, Binary Search tree and its Operations 26
Complete Binary Tree, Heaps, Heap Operations
Applications of Heaps, Priority Queue, Heap Sort
Concept , Algorithm and Implementation, Complexity, Comparison with Quick and Merge Sort 27
Types of Binary trees, Expression Tree, Threaded Binary Tree, AVL Tree, Red-Black, Splay, Insertion and Deletion Operations, Time Complexity, B–trees 28
Graphs, Terminology and Representation of Graphs
Operations on Graphs, Graph Traversals, Breadth First Search (BFS), Depth First Search (DFS)

44. Revision – Lectures 29 – 32 29 30 31 32 Lecture Topics
Shortest Path Problem, Dijkstra’s Algorithm, Bellman Ford Algorithm, Spanning Tree, Minimum Spanning Tree, Kruskal and Prim Algorithm 30
Dictionaries, Table, Concept, Operations and Implementation, Hash Table, Hashing and Hash Function, Hash Tables Implementation, Applications 31
Hash Function, Properties of a Good Hash Function
Hash Function Methods, File, Text and Binary Files
Operations on Files, File Access Methods, Sequential Files, Indexed Files, Hashed Files 32
File operations implementation in C, File operations on Text and Sequential Binary Files, Revision

45. Summary File Implementation in C Language Basic File Operations
Opening a file
Reading data from a file
Writing data to a file
Closing a file
File operations on Text Files
File operations on Sequential Binary Files
Revision of the Course
Lecture 1 to Lecture 31