Input/Output Classes in C#

Introduction

In memory, objects cease to exist when a program ends. But files exist until deletion. With files we persist data. A file is a collection of data stored in a disk with a specific name and a directory path. When a file is opened for reading or writing, it becomes a stream. The stream is basically a sequence of bytes passing through the communication path. There are two main streams, the input stream and the output stream.

The input stream is used for reading data from a file (read operation) and the output stream is used for writing into the file (write operation). We handle them with types in System.IO.

Various Types of C# I/O Classes

The System.IO namespace has various classes for performing various operation with files, like creating and deleting files, reading from or writing to a file, closing a file and so on.

Some important classes are as follows:

I/O Class	Description
FileStream	Used to read from and write to any location in a file
BinaryReader	Reads primitive data from a binary stream
BinaryWriter	Writes primitive data in binary format
File	Use for manipulating files
StreamReader	Used for reading characters from a byte stream
StreamWriter	Is used for writing characters to a stream
StringReader	Is used for reading from a string buffer
StringWriter	Is used for writing into a string buffer
Directory	Helps in manipulating a directory structure
DirectoryInfo	Used for performing operations on directories

Now we see examples of some important I/O class and examine the outputs.

The FileStream Class

The FileStream class in the System.IO namespace helps in reading from, writing to and closing files. This class derives from the abstract class Stream. You need to create a FileStream object to create a new file or open an existing file. The syntax for creating a FileStream object is as follows:

For example, create a FileStream object F for reading a file named Example.txt as:
Now we see the meaning of each parameter.

FileMode

The FileMode enumerator defines various methods for opening files. The members of the FileMode enumerator are:

Mode	Description
Append	It opens an existing file and puts cursor at the end of file, or creates the file, if the file does not exist
Create	It creates a new file. If file is already exist then it will overrite that file
CreateNew	It will also use to create a new file If the file is already exist then it will throw an Exception
Open	It opens an existing file
OpenOrCreate	It specifies to the operating system that it should open a file if it exists, otherwise it should create a new file
Truncate	It opens an existing file and truncates its size to zero bytes

FileAccess

The FileAccess enumerator defines the kind of task to do with the file.

AccessMode	Description
Read	Data can be write from file
Write	Data can be write written to the file
ReadWrite	Data can be written to and read from the file

FileShare

This enumerator applies the type of permission for sharing.

SharingMode	Description
Inheritable	It allows a file handle to pass inheritance to the child processes
None	It declines sharing of the current file
Read	It allows opening the file for reading
ReadWrite	It allows opening the file for reading and writing
Write	It allows opening the file for writing

Example

The following program shows the use of the FileStream class:



Stream Reader and Stream Writer

The StreamReader and StreamWriter classes are used for reading from and writing data to text files. These classes inherit from the abstract base class Stream that supports reading and writing bytes into a file stream.

The StreamReader Class

The StreamReader class also inherits from the abstract base class TextReader that represents a reader for reading series of characters. The following table describes some of the commonly used methods of the StreamReader class:

Method Name	Description
public override void Close()	It closes the StreamReader object and the underlying stream and releases any system resources associated with the reader.
public override int Peek()	Returns the next available character but does not consume it
public override int Read()	Reads the next character from the input stream and advances the character position by one character