The .Net framework provides a few basic classes for creating, reading and writing to files on the secondary storage and for retrieving file system information. They are located in the System.IO namespace and used both in desktop applications and the web applications.

Introduction

The .Net framework provides a few basic classes for creating, reading and writing to files on the secondary storage and for retrieving file system information. They are located in the System.IO namespace and used both in desktop applications and the web applications. We can categorise our file handling jobs in two parts –

1.     Implementing File Input and Output Operations – this involves reading and writing from and to a file saved on the disk. When a file is opened, the data from the file is stored into a sequence of bytes called Stream. Your program uses this stream to retrieve or store data. C# provides a FileStream class and as well as StreamReader and StreamWriter classes to read from and write to a byte stream. Again, data could be binary data, instead of sequence of bytes. For that we have BinaryReader and BinaryWriter classes.

2.     Working with the File System – this involves accessing the files and directory present in your system and performing typical file system operations such as copying files and creating directories. System.IO namespace provides classes working with the file system of a machine as seen by the server. These classes could be categorised into two parts:

 

·        Directory and File classes: these classes provides the static methods that allow retrieving information about any files and directories

·        DirectoryInfo and FileInfo classes: these classes use similar instance methods and properties.

Both group of classes provide similar methods and properties, the difference being –  you need to have a DirectoryInfo or FileInfo object to use the methods of second group of classes, whereas the static methods of first group of classes are always available.

Implementing the File Input and Output Operations

The System.IO namespace includes various classes, which are used to perform operations, like file creation, file deletion, and the read-write operations to files. Before moving into details, let us have a look at the commonly used class of the System.IO namespace.

Class Name	Description
FileStream	Is used to read from and write to any location within a file
BinaryReader	Is used to read primitive data types from a binary stream
BinaryWriter	Is used to write primitive data types in binary format
StreamReader	Is used to read characters from a byte stream
StreamWriter	Is used to write characters to a stream
StringReader	Is used to read from a string buffer
StringWriter	Is used to write into a string buffer
DirectoryInfo	Is used to perform operations on directories
FileInfo	Is used to perform operations on files

 

The FileStream Class

You need to create a FileStream object to open an existing file or create a new file. The syntax for this is as follows:

FileStream <object name> = new FileStream(<File Name>, <FileMode>, <File Access>, <File Share>);

For example:

FileStream fs = new FileStream(“myfile.txt”, FileMode.Open, FileAccess.Read, FileShare.Read);

The FileMode Enumerator

This enumerator defines various methods for opening files. Parameters to it checks whether a file is overwritten, created or opened. The members of the FileMode enumerator are:

Parameter	Description
Append	Opens the file if it exists and places the cursor and the end of the file, or creates a new file.
Create	Creates a new file.
CreateNew	Specifies to the operating system that a new file should be created.
Open	Opens an existing file
OpenOrCreate	Specifies to the operating system that it should open a file if it exists; else, it should create a new file
Truncate	Opens an existing file and truncates it to zero byte.

 

The FileAccess Enumerator

Unless specified, the file is opened for both reading and writing. This enumerator has members: Read, Write, and ReadWrite.

The FileShare Enumerator

This enumerator contains constants for controlling the sharing of a file by other FileStream objects; it typically sets whether two different applications can simultaneously read from same file. The members are:

Parameter	Description
Inheritable	Allows a file handle to pass inheritance to the child processes
None	Declines sharing of a current file
Read	Allows opening of a file for reading
ReadWrite	Allows opening of a file for reading and writing
Write	Allows opening of a file for writing

 

The StreamReader and StreamWriter        

The abstract Stream class is used to read from and to write data in the text files by keeping the data into a stream.  The StreamReader and StreamWriter classes inherit from two more abstract classes TextReader and TextWriter classes to accomplish the process of reading and writing.

The following code demonstrates copying text from one file to another:

using System;

using System.IO;

class FileCopy

{

public void copyfile()

{

      FileStream f1 = new FileStream("source.txt", FileMode.Open, FileAccess.Read);

      FileStream f2 = new FileStream("target.txt", FileMode.Append, FileAccess.Write);

      StreamReader sr = new StreamReader(f1);

      StreamWriter sw = new StreamWriter(f2);

   // position the file pointer at beginning of the file

                sr.BaseStream.Seek(0, SeekOrigin.Begin);

              string str = sr.ReadLine();

     while(str)

      {

         sw.WriteLine(str);

         sw.Flush(0;

         str = sr.ReadLine();

        }

             sr.Close();

             sw.Close();

              f1.Close();

               f2.Close();

     }

public static void Main()

{

       FileCopy fc = new FileCopy();

         fc.copyfile();

}

}

Working with the Windows File System

The .Net framework provides few basic classes for retrieving the file system information. These classes help retrieving information about existing files and directories and performing typical file operations like copying files and creating directories.

The DirectoryInfo and FileInfo class

Both these classes are derived fro the FileSystemInfo class. So they share a common set of properties and methods.  Let us have a look into the common methods and properties first and then we will discuss the unique properties of both the classes.

Common DirectoryInfo and FileInfo members:

Member	Description
Attributes	Allows to retrieve or set attributes associated with the current directory or file
CreationTime, LastAccessTime, and LastWriteTime	Gets or sets the time of creation, last access or last write for the file or directory respectively using a DateTime object
Exists	Gets a Boolean value indicating whether the directory or file exists or not
FullName, Name and Extension	Gets a string containing the full path, name and file extension respectively for a file or directory
Delete()	Removes the file or directory
Refresh()	Updates the object to synchronize with any file system change
Create()	Creates the specified directory or file
MoveTo()	Copies the directory and its contents or the file.

Unique DirectoryInfo members:

Member	Description
Parent and Root	Returns a DirectoryInfo object presenting parent or root directory
CreateSubDirectory()	Creates a sub directory
GetDirectories()	Returns an array of DirectoryInfo object representing the directories in the current directory after matching all the criteria. It also allows to search subdirectories within directories
GetFiles()	Returns the files in the current directory, an array of FileInfo objects.

Unique FileInfo members:

Member	Description
Directory	Returns a DirectoryInfo object that represents the parent directory
DirectoryName	Returns a string indentifying the parent directory
Length	Gets the size of file in bytes
CopyTo()	Copies a file to the new path and filename specified as parameters.
Create() and CreateText()	Creates the file and returns a FileStream object and CreateText() returns a StreamWriter object that wraps the stream
Open(), OpenRead(), OpenText(), and OpenWrite()	Opens a file if it exists. OpenRead() and OpenText() open  a file in read only mode, returning a FileStream or StreamReader. OpenWrite() open a file in write only mode, returning a FileStream.

The following code shows the use of the above mentioned classes:

using System;

using System.IO;

namespace Files_in_window

{

 class FileChecker

   {

            public static void Main()

            {

           

            DirectoryInfo dirinfo = new DirectoryInfo(@"C:\WINDOWS");

//get all the files in the directory and their name and size

            FileInfo [] filelist = dirinfo.GetFiles();

            foreach (FileInfo file in filelist)

            Console.WriteLine( " File Name: {0}  Size:  {1} bytes", file.Name, file.Length );

            }

    }

}

 

The DriveInfo class

This class is new in .Net 2.0. It allows  retrieving information about a drive on your computer. It is typically used to retrieve information like total amount used and free space.

The members of the DriveInfo Class

Member	Description
TotalSize	Gets the total size of the drive in bytes
TotalFreeSpace	Gets total amount of free space in bytes
AvailableFreeSpace	Gets total amount of available space in bytes
DriveFormat	Return the name of the file system like NTFS or FAT32
DriveType	Returns a vlue from the DriveType enumeration indicating whether the drive type is fixed, network, CD_ROM,RAM or removable drive
IsReady	Returns a Boolean value stating whether the drive is ready for reading or writing
Name	Returns the drive letter name
VolumeLabel	Returns the descriptive volume label for the drive
RootDirectory	Returns a DirectoryInfo object for the root directory of the drive
GetDrives()	Retrieves an array of DriveInfo objects representing all the drives in your computer.

Conclusion:

Working with files is required both in web applications as well as desktop applications. In this article, I have tried to describe File handling using C#. It is a vast topic, so it was not possible to give an exhaustive description. Hope you find it useful.

Happy Programming!

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NAME: PIYALI SENGUPTA

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