C# 0 The Complete Reference

EndOfStreamException

 when the 

end of the stream is reached, the program simply reads the file until either it finds the 

desired item or this exception is generated. Thus, no special mechanism is needed to detect 

the end of the file.

Random Access Files

Up to this point, we have been using 

sequential files,

 which are files that are accessed in a 

strictly linear fashion, one byte after another. However, you can also access the contents of a 

file in random order. One way to do this is to use the 

Seek( )

 method defined by 

FileStream

.

This method allows you to set the 

file position indicator

 (also called the 

file pointer

 or simply 

the

current position

) to any point within a file.

The method 

Seek( )

 is shown here:

long Seek(long 

newPos

, SeekOrigin 

origin

)

Here, 

newPos

 specifies the new position, in bytes, of the file pointer from the location specified 

by

origin.

 The origin will be one of these values, which are defined by the 

SeekOrigin

enumeration:

Value

Meaning

SeekOrigin.Begin

Seek from the beginning of the file.

SeekOrigin.Current

Seek from the current location.

SeekOrigin.End

Seek from the end of the file.

After a call to 

Seek( )

, the next read or write operation will occur at the new file position. 

The new position is returned. If an error occurs while seeking, an 

IOException

 is thrown. 

If the underlying stream does not support position requests, a 

NotSupportedException

 is 

thrown. Other exceptions are possible.

Here is an example that demonstrates random access I/O. It writes the uppercase 

alphabet to a file and then reads it back in nonsequential order.

// Demonstrate random access.

using System;

using System.IO;

class RandomAccessDemo {

  static void Main() {

    FileStream f;

    char ch;

    try {

      f = new FileStream("random.dat", FileMode.Create);

    }

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