File Handling and Preprocessor Directives

UNIT III : File Handling and Preprocessor
Directives
By
Mr.S.Selvaraj
Asst. Professor (SRG) / CSE
Kongu Engineering College
Perundurai, Erode, Tamilnadu, India
Thanks to and Resource from : Sumitabha Das, “Computer Fundamentals and C Programming”, 1st Edition, McGraw Hill, 2018.
20CST21 – Programming and Linear Data Structures

Syllabus – Unit Wise
6/9/2021 3.1 _ File Handling Basics 2

List of Exercises

Text Book and Reference Book

Unit III : Contents
1. File Handling Basics
2. Text and Binary files
3. Opening and closing files
4. Detecting the End-Of-File, File pointer and file buffer
5. File read/write functions
6. Formatted functions fscanf() and fprintf()
7. Reading and writing binary files
8. Manipulating file position indicator
9. Renaming and Removing a file
10. Command line Arguments
11. Preprocessor
12. #define macros with and without arguments
13. #include directive
14. Conditional Compilation
6/9/2021 5
3.1 _ File Handling Basics

File Handling Basics
• So far, the input to the C programs is given from the
prompt / terminal.
• When a program is terminated, the entire input data is
lost.
• Storing in a file will preserve the data even if the program
terminates.
• Also to handle a large number of data, it will take a lot of
time to feed them through the terminal.
• If those data are stored in a file, then it is easy to access
them from the file using the file handling functions in C.
• In C programming, a file represents a sequence of bytes on
the disk where a group of related data is stored.
• All file handling functions are available in <stdio.h> header
file.

Types of Files
• There are two types of files exists in C
Programming.
• They are:
– Text files
– Binary files

Text Files
• Text files contain ASCII codes of digits, alphabetic and
symbols.
• Text files are the normal files that can be easily created
using Notepad or any simple text editors with an extension
“.txt”.
• When opening those files, it is possible to see all the
contents as plain text.
• We can easily edit or delete the contents.
• Plus and Minus of Text Files:
– They take minimum effort to maintain (+)
– Easily readable (+)
– provide least security (-)
– takes bigger storage space (-)

Binary Files
• Instead of storing data in plain text, they store it
in the binary form (0's and 1's).
• Binary files usually have an extension “.bin”.
• Plus and Minus of Binary Files:
– They can hold higher amount of data (-)
– not readable easily (-)
– provides a better security than text files (+)
• For example, given the integer number 12345.
– we could store it as individual characters 1, 2, 3, 4,
and 5, using one byte for each character in text file as

• 1. Opening a New/Existing file
• 2. Writing data into a file
• 3. Reading data from the file
• 4. Closing a file
Operations on Files
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Opening a New/Existing file
• When working with files, it is mandatory to declare a
pointer of type FILE as below:
• The FILE is a structure data type defined in <stdio.h>.
• This declaration is needed for communication between
the file and program.
• A file should be opened before any operation is being
performed on it.

• The syntax of fopen() is given by,
• In the above format, the arguments “path”
and “mode” are strings.
• The fopen()
– returns a pointer to FILE structure on success
– else it returns NULL.

• Every file on the disk has a name known as
filename.
• The filename can be specified as either
absolute path or relative path.
• In the absolute path, the complete location of
the file is given whereas only partial path is
mentioned in the relative path.

• The file mode specifies the kind of operation performed on the
file.
• The various file modes are given in the following table:

Create a New File using fopen()
• To create a new text file “file1.txt”, we can open
the file in write mode(“w”) as given below:
• In the above example, suppose the file “file1.txt”
already exist in the location E:CPrograms.
• The fopen() removes all the contents from the
file “file1.txt” and creates a new empty file
named “file1.txt”.
• If “file1.txt”does not exist, new empty file
named “file1.txt” is created.

Read file contents
• To read the contents of the text file “sample.txt”, we
can open the file in read mode(“r”) as given below:
• In the above example, suppose the text file
“sample.txt” exists in the current working directory.
• The function fopen() opens the file for reading in text
mode.
• The reading mode only allows us to read the file, we
cannot write into the file.

Difference between Append and Write Mode
• Both write (w) mode and append (a) mode are used to
write data into a file.
• In both the modes, new file is created if it doesn't exist
already.
• The only difference is, when a file is opened in the
write mode, the file is reset, resulting in deletion of
any data already present in the file.
• While in append mode this will not happen.
• Append mode is used to append or add data to the
existing data of file (if any).
• Hence, when a file is opened in append (a) mode, the
file pointer/cursor is positioned at the end of the file.

Example 1

Example 2:
char filename[80];
FILE *fp;
printf(“Enter the filename to be opened”);
gets(filename);
fp = fopen(filename,“w”);
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Example 2

• The file should be closed after performing read/write
operation.
• Closing of a file is performed using the function
fclose().
• Closing a file frees the file pointer (file pointer is
disconnected from a file) and associated buffers.
• The fclose() will close the file specified by the fptr
whereas the fcloseall() closes all the files that are
already opened.
• The fclose() function
– returns 0 if close operation is successful or
– returns EOF if an error was encountered.
Closing a File
6/9/2021 21

Detecting the End-of-File (EOF)
• While performing read and write operations
on files, we do not know exactly how long the
file is.
• Usually, we read data from the beginning to
the end of the file.
• To identify the reach of end-of-file (EOF),
there are two ways available.

Way 1
• While reading the file in text mode by character
at a time, we can compare the character that has
been read with EOF, which is a symbolic constant
defined in stdio.h whose value is set to -1.
• The following code snippet does that,

Way 2
• The other way is the use of feof( ) function defined in
stdio.h.
• The syntax of feof( ) is given by:
• The function returns 0 (false) when the end of the file
has not been reached and a non-zero value (true) if
the EOF has been reached.
• A simple code snippet using feof( ) is given as

• fopen has two important consequences
– creation of a file pointer and file buffer
• File pointer is a variable that points to a structure
typedef to FILE.
• FILE contains the following information related to
the opened file
– The mode of opening.
– The location of the file buffer.
– The file position indicator.
– Whether EOF or any errors have been encountered on
reading or writing.
• File position indicator also called file offset pointer,
plays important role in input/output operations
Detecting the file pointer and file buffer
6/9/2021 25

• When a file is read with fgetc, data is first sent
from disk to the buffer.
Detecting the file pointer and file buffer
6/9/2021 26

Example 3:
FILE *fp;
fp = fopen(“data.dat”,“r”);
if(fp == NULL)
{
printf(“Can not open data.datn”);
exit(1);
}
Or
FILE *fp;
if((fp = fopen(“data.dat”, “r”)) ==NULL)
{
printf(“Can not open data.datn”);
exit(1);
}
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Detecting File Pointer

Thank you

Unit III : Contents
11. Preprocessor
6/9/2021 30
3.2 _ Reading and Writing Functions in Files

Input and Output Operations
• A C program can read data from the keyboard and
writes data into the monitor.
• Similarly, it can read and write from/into the file as
shown in the diagram.
6/9/2021 3.2 _ Reading and Writing Functions in Files 31

Input and Output Operations
• A number of functions are available for
performing operations on files.
• They are classified as formatted File I/O and
unformatted File I/O functions.
• The formatted functions deal with all kind of
data whereas the unformatted functions deal
only character data type.
• Different functions are also available for
handling text as well as binary files.

List of read/input functions
• To perform read operations the following
functions are used.
– fgetc ( )
– fgets ( )
– fscanf ( )
– fread ( )

List of write/output functions
• To perform read operations the following
functions are used.
– fputc ( )
– fputs ( )
– fprintf ( )
– fwrite ( )

• Character-oriented functions (fgetc and fputc)
• Line-oriented functions (fgets and fputs)
• Formatted functions (fscanf and fprintf)
• Array- and structure-oriented functions (fread
and fwrite)
• All the functions use the file pointer as
argument and work with any file including
stdin, stdout and stderr.
List of Read/Write functions
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3.2 _ Reading and Writing Functions in Files

Reading and Writing to a text file using fgetc () and fputc ()
• fgetc () reads the content of the file character by
character.
• After reading a character from the file, fgetc() function
moves the file pointer to next character in the file.
• The fgetc () function returns the next character from
the file specified.
• It returns EOF if end-of-file is reached or error
occurred.

Example 1
• Assume there is a text file “file1.txt” with the
content “Hello World!” . Write the C program
to read that file one character at a time using
fgetc() function and display it on the monitor.

fputc ( ) function
• The function fputc ( ) writes a character to the
specified file and automatically advances the file
pointer to the next position in the file.
– On success, the written character is returned by the
function.
– If pointer is at end of file or if an error occurs EOF file
is returned by this function.
• Syntax:
– char − This is the character to be written.
– fptr − This is the pointer to a specified file that
indicates where the character is to be written.

Example 2
• Write a c program to write the string
“Engineers create the World” in the file
sample.txt using fputc() function.

Reading and Writing to a text file using fgets () and fputs ()
• The function fgets() is used to read a file line by line.
– str − This is the pointer to an array of characters where
the string read is stored.
– size − This is the maximum number of characters to be
read (including terminating character “0”). Usually, the
length of the array “str” is used.
– fptr − This is the pointer that identifies the file where
characters are read from.

Reading and Writing to a text file using fgets () and fputs ()
• fgets ( ) reads a line from the specified file and stores
it into the string pointed to by str.
– It stops when (size-1) characters are read or
– the newline character is read, or
– the end-of-file is reached, whichever comes first.
• While all the characters are read without any error, a
null (“ 0” ) character is appended to the end of the
string.
• On success, fgets () returns the same str parameter.
• If end-of-file is encountered or an error occurred, a
NULL value is returned.

Example 3
• Again consider the text file “file1.txt”. Now,
write a C program to read the file using fgets()
function and read 4 characters at a time and
those are displayed in the monitor.

fputs ( ) function
• This function is used to write a string into the file.
• It has two arguments,
– pointer to string and
– file pointer.
• It writes a null-terminated string to the file.
• The null character is not written to the file.
• On success, fputs( ) returns Non-negative value.
• On error, it returns EOF or Negative value.
• str − This is an array containing a string (terminated by
“0”) to be written into a file.
• fptr − This is the pointer to a specified file that
identifies the stream where the string is to be written.

Example 4
• Write a C program to write 5 strings into the
file sample.txt using fputs() function.

Reading and Writing to a text file using fscanf() and fprintf ()
• For reading and writing to a text file, we use
the functions fscanf() and fprintf() .
• They are just the file versions of scanf()
and printf().
• The only difference is that fscanf() and fprint()
expects a pointer to the structure FILE.
• Other functions like fgetchar(), fputc() etc. can
be used in a similar way.

fscanf ( ) function
• The functions fgetc ( ) and fgets ( ) are used for
reading only character data.
• But, fscanf ( ) can read different types of data
such as int, float, char, etc., from the given file.
• On success, this function returns the number of
input items successfully matched and assigned
to argument specified.
• On failure, it returns EOF.

fscanf ( ) function
• The parameters used in the fscanf() are:
– fptr − This is the pointer that identifies the file where
characters are read from.
– format-string – This is a string which controls the
interpretation of the argument list. A format
specification causes the fscanf() function to read and
convert characters in the input into values of a
specified type.
– argument-list - The value read from the file based on
format-string is assigned to an argument in the
argument list.

Example 5
• Write a C program to Read the integer
number from a file sample.txt using fscanf()
function.

fprintf () function
• Like fscanf( ), the function fprintf( ) handles
different types of data.
• It can be used for writing formatted data into
the file.
• On success, fprintf( ) returns the total number
of bytes written to the file.
• On error, it returns EOF.

Example 6
• Write a C program to Read the details about n
students from the user and write those
information into the file sample.txt using
fprintf() function.

Reading and Writing to a text file using fread() and fwrite ()
• The functions fgetc(), fgets() and fscanf() are used to
read data from text files.
• The function fread() is used to get data from binary
files.
• In binary files, information is stored in the form of
binary and it can be read directly into memory with no
need of any processing to interpret it.
• Hence, handling of files in binary mode is significantly
faster than text mode.
• On success, fread() returns the number of items read
from the file.
• On error or EOF, it returns a number less than “n”.

fread() function
• Syntax:
– ptr – It is the starting address of the memory block where
data is to be read.
– size – Item size in bytes.
– n- It indicates the maximum number of items read from
the file
– fptr –It specifies the pointer to file from where the data
has to be read.
• The following code snippet discuss about the different
ways in which fread() can be used.

fwrite() function
• fwrite( ) function is used to write binary data into the
file.
• It accepts the same arguments as fread( ).
• Syntax:
• On success, it returns the number of items successfully
written to the file.
• On error, it returns a number less than n.
• The following code snippets show the usage of fwrite()
function in handling different data.

The first fwrite( ) function writes only
the first three elements of the array
into the file. But, the second one
writes the last three elements of the
array into the file.

Example 7
• Write a C Program to Write the details about 3
students into the file sample.txt using fwrite()
function.

Practice Problem 1
• Get a line of text from the user and write it
into a file named „sample.txt‟. Read the
contents from the file and display it on the
monitor. Use fgetc() and fputc() functions to
manipulate the file.

Practice Problem 2
• Write a program to copy the content of one
file into another one. Get the source and
target file names from the user.

Practice Problem 3
• Write a C program to compare two files for
checking whether two files contains the same
content or not.

Practice Problem 5
• Write a program to add some content at the
end to the existing file.

Practice Problem 5
• Write a program to get the details (such as
Name, Roll No, five subjects marks ) of N
students and find the Total mark and Rank for
each student. Write Name, RollNo, Total mark
and Rank for each student into a file named
“studentdb.txt” using formatted file I/O
functions and also display these details in
tabular format.

Practice Problem 6
• Write a program to create and manage a student
database with the listed operations
1. Add a new student by giving his/her roll number,
name and average mark.
2. Display the details about a student for a given roll
number
3. Display the details of all students in the database
4. Update the average mark of a student for a given roll
number
5. Delete a student record if roll number is given

Thank you

Unit III : Contents
11. Preprocessor
6/9/2021 73
3.3 _ Manipulating, Removing and
Renaming a File

Sequential Access and Random Access Files
• Based on the method of accessing the data stored, files
can be classified into two types.
– Sequential access file
– Random access file
• In the sequential access file, data is kept in sequential
order. To access the last record of the file, we need to
read all records preceding to that record.
– Hence, it takes more time.
• But, in random access files data can be read and
modified at any random position. Unlike sequential
access, the any record can be read directly.
– Hence, it takes less time.
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Renaming a File
74

Difference b/w Sequential and Random Access Files
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Renaming a File
75

Random Accessing in Files
• To achieve random accessing in files, the
following functions are used
– fseek()
– ftell()
– rewind()
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Renaming a File
76

Manipulating file position indicator using
fseek( ) function
• If there are many records inside a file and
need to access a record at a specific position
fseek( ) is used.
• As the name suggests, fseek() moves file
pointer associated with a given file to a
specific position.
• The fseek() function returns 0 if the move is
successful, else it returns a non-zero value.
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Renaming a File
77

fseek() function
• fptr - It is the pointer to the file.
• Offset - It indicates the number of bytes to move from
the position specified by the third argument. The
positive value of offset makes the move in the forward
direction whereas the negative value in the
backward(reverse) direction.
• Position - It defines the point with respect to which the
file pointer needs to be moved. It has three values:
6/9/2021
Renaming a File
78

Example
6/9/2021
Renaming a File
79

ftell( ) function
• The ftell() function is used to return the
position of file pointer in the file with respect
to starting of the file.
6/9/2021
Renaming a File
80

Example
• The value of p is 12 which also indicate the
size of the file.
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Renaming a File
81

rewind( ) function
• The rewind function sets the file position to
the beginning of the file.
• The rewind( ) is equivalent to
– fseek (fptr, 0, SEEK_SET).
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Renaming a File
82

Example
• Write a program to reverse the contents of
the text file using fseek() function.
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Renaming a File
83

6/9/2021
Renaming a File
84

Removing a file : remove ( ) function
• The remove function can be used to delete a
file that is not opened already.
• The function returns zero if file is deleted
successfully, else returns a non-zero value.
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Renaming a File
85

Renaming a file: rename ( ) function
• The function rename() is used to change the
name of the file
• i.e. from old_name to new_name without
changing the content present in the file.
• Syntax:
– If the file is renamed successfully, zero is returned.
– On failure, a nonzero value is returned.
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Renaming a File
86

Thank you
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Renaming a File
87

Unit III : Contents
11. Preprocessor
6/9/2021 89
3.4 _ Command Line Arguments

Command-line Arguments
• Command line argument is a parameter
supplied to the program when it is invoked.
• It is possible to pass values from the
command line to the C programs when they
are executed.
• These values are called command line
arguments.
• Executable code of the program should be
compiled from DOS prompt.
6/9/2021 3.4 _ Command Line Arguments 90

• The command line arguments are handled by
arguments given in main() function.
• The main() can be defined as,

• The first argument argc refers to the number
of arguments passed to main().
• and the second argument argv[] is an array of
character pointers which points to each
argument passed to the main().

• The array argv contains the elements
– argv[0] holds the name of the program itself.
– argv[1] is a pointer to the first command line argument
supplied
– argv[2] is a pointer to the second command line argument
supplied
– …….
– argv[argc-1] is a pointer to the last command line
argument supplied to the program.
• If no argument is supplied to the program, the
parameter argc will be set to one.
• if one argument is passed then argc is set to 2.

• Steps to be followed to execute program using
Command Line Argument inside Borland C Compiler :
– Step 1 : Enter a Program and compile it.
– Step 2 : Open File menu inside Borland C.
– Step 3 : Click on DOS Shell.
– Step 4 : In the Command Prompt type the filename
(Program name without any extension) with the
arguments and press Enter Key using the format “filename
value 1 value 2 ..... Value m” . Program will be executed
with the given arguments and output is generated.
– Step 5 : Type “exit” command to return to Borland C

Example 1
• Write an example program to checks if there
is any argument supplied from the command
line and display these arguments.

Example 2
• Write a program to add all the numbers given
as Command Line Arguments.

Example 3
• Write a program to copy one file into another
file using command line argument.

Problem 1

Thank you

Unit III : Contents
11. Preprocessor
6/9/2021 106
3.5 _ Preprocessor

Preprocessor
• As the name suggests preprocessors are programs that
processes the source code before compilation as shown in
figure.
• Preprocessor provides preprocessor directives which tell
the compiler to preprocess the source code before the
complier starts its work.
• All the preprocessor directives begin with a “#” (hash)
symbol.
• The preprocessor directives can be placed anywhere in the
program.
6/9/2021 3.5 _ Preprocessor 107

Types of Preprocessor directives
• There are three different types of
preprocessor directives :
– Macros
– File Inclusion
– Conditional Compilation
6/9/2021 3.5 _ Preprocessor 108

Macros
• Macros are piece of code in a program which
is assigned with some name.
• Whenever this name is encountered by the
compiler the compiler replaces the name with
the actual piece of code.
• The “#define” directive is used to define a
macro.
• There are two types of macros –
– one which takes the argument and
– another which does not take any argument.
6/9/2021 3.5 _ Preprocessor 109

Difference between Macros and Functions
6/9/2021 3.5 _ Preprocessor 110

Macros without argument
• Every occurrences of macro name is replaced
with the actual piece of code by the compiler.
• This kind of macros usually used to give symbolic
names to numeric constants.
• There is no semi-colon(“;‟) is needed at the end
of a macro definition.
6/9/2021 3.5 _ Preprocessor 111

Example
6/9/2021 3.5 _ Preprocessor 112

Macros with arguments
• It is also possible to pass arguments to
macros.
• Macro with arguments works similarly as
functions.
6/9/2021 3.5 _ Preprocessor 113

Example
6/9/2021 3.5 _ Preprocessor 114

Nesting of macros
• macro may be used in the definition of
another macro. This is known as nesting of
macros.
6/9/2021 3.5 _ Preprocessor 115

Example
6/9/2021 3.5 _ Preprocessor 116

File Inclusion
• The #include preprocessor is used to include
header files to a C program.
• This directive instructs the compiler to include a
specified file to the C program.
• Here, "stdio.h" is a header file.
• The #include preprocessor directive replaces the
above line with the contents of stdio.h header
file which contain function and macro definitions.
6/9/2021 3.5 _ Preprocessor 117

File Inclusion
• Rules for file inclusion are:
– 1. File inclusive Directives are used to include
standard or user define header file inside C Program.
– 2. File inclusive directory checks included header file
inside same directory (if path is not mentioned).
– 3. File inclusive directives begins with #include
– 4. If Path is mentioned then it will include the header
file present in the location specified by that path.
– 5. Instead of using triangular brackets we use “Double
Quote” for inclusion of user defined header file.
6/9/2021 3.5 _ Preprocessor 118

Including Standard Header Files
6/9/2021 3.5 _ Preprocessor 119

Including User Defined Header Files
6/9/2021 3.5 _ Preprocessor 120

Conditional Compilation
• Conditional compilation is the process of selecting
which code to compile and which code to not compile
similar to the #if / #else / #endif in C and C++.
• Conditional Compilation directives helps to include or
skip a specific block of code in the source code based
on some conditions.
• This can be done with the help of “ifdef” and “endif”
preprocessing directives.
• If the macro in #ifdef is defined, then the block of
statements will be executed normally. But, if it is not
defined, then the compiler will simply skip that block
of statements.
6/9/2021 3.5 _ Preprocessor 121

Conditional Compilation
6/9/2021 3.5 _ Preprocessor 122

Example
6/9/2021 3.5 _ Preprocessor 123

Thank you
6/9/2021 3.5 _ Preprocessor 124

File Handling and Preprocessor Directives

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