File Processing

Files and Streams

C views each file simply as a sequential stream of bytes. Each file ends either with an end-of-file markeror at a specific byte number recorded in a system-maintained, administrative data structure.

When a file is opened, a stream is associated with it.

treams provide communication channels between files and programs. Three files and their associated streams are automatically opened when program execution begins:

• the standard input to read data from the keyboard
• the standard output to print data on the screen.
• the standard error

File Definition

A file represents a sequence of bytes on the disk where a group of related data is stored. File is created for permanent storage of data. It is a ready made structure.

In C language, we use a structure pointer of file type to declare a file.

Opening and Closing Files

The fopen() function is used to create a new file or to open an existing file.

General Syntax:

*fp = FILE *fopen(const char *filename, const char *mode);

Here, *fp is the FILE pointer (FILE *fp), which will hold the reference to the opened(or created) file.

filename is the name of the file to be opened and mode specifies the purpose of opening the file. Mode can be of following types,

mode	description
r	opens a text file in reading mode
w	opens or create a text file in writing mode.
a	opens a text file in append mode
r+	opens a text file in both reading and writing mode
w+	opens a text file in both reading and writing mode
a+	opens a text file in both reading and writing mode
rb	opens a binary file in reading mode
wb	opens or create a binary file in writing mode
ab	opens a binary file in append mode
rb+	opens a binary file in both reading and writing mode
wb+	opens a binary file in both reading and writing mode
ab+	opens a binary file in both reading and writing mode

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Closing a File

The fclose() function is used to close an already opened file.

General Syntax :

int fclose( FILE *fp);

Here fclose() function closes the file and returns zero on success, or EOF if there is an error in closing the file. This EOF is a constant defined in the header file stdio.h.