File management

A File can be used to store a large volume of persistent data. Like many other
languages 'C' provides following file management functions,
Creation of a file
Opening a file
Reading a file
Writing to a file
Closing a file

Following are the most important file management functions available in 'C,'
Function purpose
•fopen () Creating a file or opening an existing file
•fclose () Closing a file
•fprintf () Writing a block of data to a file
•fscanf () Reading a block data from a file
•getc () Reads a single character from a file
•putc () Writes a single character to a file
•getw () Reads an integer from a file
•putw () Writing an integer to a file
•fseek () Sets the position of a file pointer to a specified location
•ftell () Returns the current position of a file pointer
•rewind () Sets the file pointer at the beginning of a file

Whenever you want to work with a file, the first step is to create a
file.
A file is nothing but space in a memory where data is stored.
To create a file in a 'C' program following syntax is used,
FILE *fp;
fp = fopen ("file_name", "mode");
In the above syntax, the file is a data structure which is defined in the
standard library.
How to Create a File

•fopen is a standard function which is used to open a file.
•If the file is not present on the system, then it is created and then
opened.
•If a file is already present on the system, then it is directly
opened using this function.
•fp is a file pointer which points to the type file.
•Whenever you open or create a file, you have to specify what
you are going to do with the file.
•A file in 'C' programming can be created or opened for
reading/writing purposes.
• A mode is used to specify whether you want to open a file for
any of the below-given purposes.

Following are the different types of modes in 'C' programming which can be used while working with a
file.
File Mode Description
r Open a file for reading. If a file is in reading mode, then no data is deleted if a file is already
present on a system.
w Open a file for writing. If a file is in writing mode, then a new file is created if a file doesn't exist
at all. If a file is already present on a system, then all the data inside the file is truncated, and it
is opened for writing purposes.
a Open a file in append mode. If a file is in append mode, then the file is opened. The content
within the file doesn't change.
r+ open for reading and writing from beginning
w+ open for reading and writing, overwriting a file
a+ open for reading and writing, appending to file
In the given syntax, the filename and the mode are specified as strings hence they must always be
enclosed within double quotes.

EXAMPLE
#include <stdio.h>
int main()
{
FILE *fp;
fp = fopen ("data.txt", "w");
}
Output:
File is created in the same folder where you have saved your code.
You can specify the path where you want to create your file
#include <stdio.h>
int main() {
FILE *fp;
fp = fopen ("D://data.txt", "w");
}

How to Close a file
•One should always close a file whenever the operations on file are over. It means the
contents and links to the file are terminated.
•This prevents accidental damage to the file.
•'C' provides the fclose function to perform file closing operation. The syntax of fclose is
as follows,
fclose (file_pointer);
Example:
FILE *fp;
fp = fopen ("data.txt", "r");
fclose (fp);

FILE I/O Operations
When a file opened, we can read data stored in the file or write new data onto it depending on the mode
of opening standard library supports a good number of functions which can be used for performing I/O
operations. These functions are referred to as file I/O functions.
File I/O functions are broadly classified into two types:
1. High level files I/O functions
2. Low level files I/O functions
•High level file I/O functions are basically C standard library functions and are easy to use.
•Most of the C programs handling files use these because of their simple nature.
•Low level file I/O functions are file related system calls of the underlying operating system.
•These are relatively more complex in nature when compared to high level file I/O functions but efficient in
nature.
• fputc() and fgetc()-Character-oriented file I/O functions fputs() and fgets()-String-oriented file I/O
functions

High level file I/O functions can be further classified into the following two types:
1. Unformatted file I/O functions
2. Low level files I/O functions
•Unformatted file I/O functions
fputc() and fgetc()-Character-oriented file I/O functions
fputs() and fgets()-String-oriented file I/O functions
• Formatted file I/O functions
fprint() and fscanf()-Mixed data-oriented file I/O functions

Command Line ArgumentsIn C it is possible to accept command line arguments.
Command-line arguments are given after the name of a program in command-line operating systems like DOS or Linux, and
are passed in to the program from the operating system.
To establish the data communication between a calling function and a called function.
It is done through arguments; a calling function passes inputs to a called function, which perform required manipulations.
To display the contents of emp.dat, we use the following command:
C:>type emp.dat
here type is the program file name (executable) and emp.dat is the input file, the contents of which are displayed
To make main() of a program take command line arguments, the function header will have the following form:
void main(int argc,char *argv[])
Here, argc and argv [] are the formal arguments, which provide mechanism for collecting the arguments given at command
line when the program is launched for execution.

SUMATHI V
ASSITANT PROFESSOR
DEPARTMENT OF COMPUTER APPLICATIONS
SRI RAMAKRISHNA COLLEGE OF ARTS AND SCIENCE
COIMBATORE-641006
TAMILNADU,INDIA

File management

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