C# 0 The Complete Reference

Close( )

 works by calling 

Dispose( )

, which actually frees 

the resources.

N

OTE

N

OTE

The

using

 statement, described in Chapter 20, offers a way to automatically close a file when 

it is no longer needed. This approach is beneficial in many file-handling situations because it 

provides a simple means to ensure that a file is closed when it is no longer needed. However, to 

clearly illustrate the fundamentals of file handling, including the point at which a file can be 

closed, this chapter explicitly calls 

Close( )

 in all cases.

Reading Bytes from a FileStream

FileStream

 defines two methods that read bytes from a file: 

ReadByte( )

 and 

Read( )

. To 

read a single byte from a file, use 

ReadByte( )

, whose general form is shown here:

int ReadByte( )

Each time it is called, it reads a single byte from the file and returns it as an integer 

value. It returns –1 when the end of the file is encountered. Possible exceptions include 

NotSupportedException

 (the stream is not opened for input) and 

ObjectDisposedException

(the stream is closed).

To read a block of bytes, use 

Read( )

, which has this general form:

int Read(byte[ ] 

buf

, int 

offset

, int 

numBytes

)

Read( )

 attempts to read up to 

numBytes

 bytes into 

buf

 starting at 

buf

[

offset

]. It returns the 

number of bytes successfully read. An 

IOException

 is thrown if an I/O error occurs. Several 

other types of exceptions are possible, including 

NotSupportedException

, which is thrown 

if reading is not supported by the stream.

The following program uses 

ReadByte( )

 to input and display the contents of a text file, 

the name of which is specified as a command-line argument. Note the program handles two 

errors that might occur when this program is first executed: the specified file not being 

found or the user forgetting to include the name of the file.

/* Display a text file.

   To use this program, specify the name of the file that you

   want to see. For example, to see a file called TEST.CS,

   use the following command line.

   ShowFile TEST.CS

*/

using System;

using System.IO;

class ShowFile {

  static void Main(string[] args) {

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