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In this tutorial, we are going to explain how to perform the random access of a file by using the Seek() method of FileStream class. The FileStream class is used to create a byte stream, which is used to write or read bytes to/from a file. The FileStream class is defined in the System.IO namespace.

The Seek() method of FileStream class

Method	Description
int Seek(int offset, SeekOrigin origin)	This method sets the current position of the file pointer, where: offset, represents the point relative to origin from which to begin seeking. origin, represents the beginning, the end, or the current position as a reference point for offset, using a value of type SeekOrigin enum(it is explained next) This method returns the new position of the file pointer in the stream.

The fields of SeekOrigin Enum

Fields	Description
SeekOrigin.Begin	Sets the file pointer to the beginning of the file, to seek from the beginning of a file.
SeekOrigin.Current	Sets the file pointer to the current position in the file, to seek from the current position.
SeekOrigin.End	Sets the file pointer to the end position in the file, to seek from the end position.

Calling the Seek() method to read a file from beginning to end.

In this example, first we will create a new file by passing its full path to the constructor of FileStream, and then we will perform the following operations:

• We will write bytes to this file i.e one byte at a time.
• Next, we call the Seek(int offset, SeekOrigin origin) method to reset its file pointer to the beginning of the file, by using the field SeekOrigin.Begin of SeekOrigin enum.
• Finally, we will read bytes from the beginning of the same file.

Note: We will use the FileMode field FileMode.Create which creates a new file and any existing file with the same name is overwritten.

//C# calling the Seek() method of FileStream class to write to a file and to read from it.

using System;
using System.IO;
using System.Text;


class A
{
public static void Main(String[] ar)
{
	try
	{
		//Creating an object of FileStream
		FileStream fs = new FileStream("D:\\Textbook8.txt", FileMode.Create);
	
		//Creating a String object 
		String str = "There is a light at the end of the tunnel, so keep fighting!.";
	
		//Creating a byte array from a String
		byte[] bA = Encoding.ASCII.GetBytes(str);  

		Console.WriteLine("Writing to a file");
		foreach(byte bt in bA)
		{
			//writing one byte at a time to the file.
			fs.WriteByte(bt);	
		}
	
		//Flushing the buffered date to the file
		fs.Flush();

		//Calling the Seek() method to set the file pointer to the beginning of the file
		fs.Seek(0, SeekOrigin.Begin);

		int c;
	
	
		//Calling the ReadByte() method to reading one byte out of a file
		Console.WriteLine("Reading the contents of the same file: ");
		while((c = fs.ReadByte()) !=-1) 
		{
			//Casting byte to char for displaying the read character on the screen
			Console.Write((char)c); 
		}

		//Closing the byte stream i.e. FileStream
		fs.Close();	
	}
	catch(IOException e)
	{
		Console.WriteLine(e);
	}

}
}
 

Output is -:

Writing to a file
Reading the contents of the same file:
There is a light at the end of the tunnel, so keep fighting!.

• In the program we gave first created a file called "Textbook8.txt" in D: drive and next, we have written its contents -:
  There is a light at the end of the tunnel, so keep fighting!.


• Next, we have called the Seek(int offset, SeekOrigin origin) method to reset its file pointer to the beginning of the file, by using the field SeekOrigin.Begin of SeekOrigin enum.


• Finally, we have read its contents from the beginning of the file by using the FileStream class.

Calling the Seek() method to read a file, from somewhere in its middle to its end.

• In this example, first we will read the same file called "Textbook8.txt" in D: drive, which was created in the previous example of this tutorial. The contents of this file are:
  There is a light at the end of the tunnel, so keep fighting!.


• We will read this file starting from the 10th offset position from the beginning of this file, to its end. For this, we will call the Seek(int offset, SeekOrigin origin) method to reset its file pointer to 10 offset position from the beginning of the file, by using the field SeekOrigin.Begin of SeekOrigin enum.

Note: We will use the FileMode field FileMode.Open which creates a open an existing file

//C# calling the Seek() method of FileStream class 
// to read a file from an offset somewhere in the middle to its end

using System;
using System.IO;
using System.Text;


class A
{
public static void Main(String[] ar)
{
	try
	{
		//Creating an object of FileStream
		FileStream fs = new FileStream("D:\\Textbook8.txt", FileMode.Open);
	
		//Calling the Seek() method to set the file pointer 10 offset from the beginning of the file
		fs.Seek(10, SeekOrigin.Begin);

		int c;
	
	
		//Calling the ReadByte() method to reading one byte out of a file
		Console.WriteLine("Reading the contents of the same file: ");
		while((c = fs.ReadByte()) !=-1) 
		{
			//Casting byte to char for displaying the read character on the screen
			Console.Write((char)c); 
		}

		//Closing the byte stream i.e. FileStream
		fs.Close();	
	}
	catch(IOException e)
	{
		Console.WriteLine(e);
	}

}
}
 

Output is -:

Reading the contents of the same file:
 light at the end of the tunnel, so keep fighting!

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