C# 0 The Complete Reference

FileStream

 class. 

FileStream

 is derived from 

Stream

 and contains all of 

Stream

’s functionality.

Remember, the stream classes, including 

FileStream

, are defined in 

System.IO

. Thus, 

you will usually include

using System.IO;

near the top of any program that uses them.

Opening and Closing a File

To create a byte stream linked to a file, create a 

FileStream

object.

FileStream

 defines 

several constructors. Perhaps its most commonly used is the one shown here:

FileStream(string 

fi lename

, FileMode 

mode

)

Here, 

filename

 specifies the name of the file to open, which can include a full path specification. 

The

mode

 parameter specifies how the file will be opened. It must be one of the values 

defined by the 

FileMode

 enumeration. These values are shown in Table 14-4. In general, 

this constructor opens a file for read/write access. The exception is when the file is opened 

using

FileMode.Append

. In this case, the file is write-only.

If a failure occurs when attempting to open the file, an exception will be thrown. If the file 

cannot be opened because it does not exist, 

FileNotFoundException

 will be thrown. If the 

file cannot be opened because of some type of I/O error, 

IOException

 will be thrown. Other

possible exceptions are 

ArgumentNullException

 (the filename is null), 

ArgumentException

(the filename is invalid), 

ArgumentOutOfRangeException

 (the mode is invalid), 

SecurityException

 (user does not have access rights), 

PathTooLongException

 (the filename/

path is too long), 

NotSupportedException

 (the filename specifies an unsupported device), 

and

DirectoryNotFoundException

(specified directory is invalid).

Value

Description

FileMode.Append

Output is appended to the end of file.

FileMode.Create

Creates a new output file. Any preexisting file by the same name 

will be destroyed.

FileMode.CreateNew

Creates a new output file. The file must not already exist.

FileMode.Open

Opens a preexisting file.

FileMode.OpenOrCreate

Opens a file if it exists, or creates the file if it does not already 

exist.

FileMode.Truncate

Opens a preexisting file, but reduces its length to zero.

T

ABLE

 14-4 

The

FileMode

 Values

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