Module 14 - Working With Files In C#

Module 14: Working with Files in C#

By SRIRAM . B

Overview 

Working with File System

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Streams

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Classes Used for I/O

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File Stream

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Stream Reader

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Stream Writer

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Random Access

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Multi threading

Working with File System 

Obtaining the Application’s Environment Information – - System.Environment Class – Properties :» - CurrentDirectory, MachineName, OSVersion, UserName, Version – Methods :» GetFolderPath, GetLogicalDrives, Exit

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Manipulating Files using System.IO.File and FileInfo classes – File is a sealed class and contains only static methods – FileInfo is a sealed class and contains only instance methods

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File Class Members – Copy, Create, Delete, Exists, Move

Working with File System.. 

GetAttributes (Returns an object of FileAttributes class)

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SetAttributes (Takes a parameter of FileAttributes)

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GetCreationTime, GetLastAccessTime, GetLastWriteTime (All returns an object of DateTime Struct)

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Open, OpenRead, OpenWrite (All returns an object of File Stream class)

Working with File System.. 

File Attribute Enumeration – Directory, Hidden, Normal, System, Temporary, ReadOnly, Encrypted, Compressed

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File Info Members – CreationTime, DirectoryName, Exists, LastAccessTime, LastWriteTime, Length, CopyTo, MoveTo, Create, Delete, Open, OpenRead, OpenWrite, OpenText

Working with File System.. 

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Manipulating Directories 

Two classes – Directory and DirectoryInfo

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Same like File and FileInfo classes

Directory Class members 

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CreateDirectory, Delete, Exists, GetDirectories, GetFiles, Move, GetParent

DirectoryInfo members 

Create, Delete, GetDirectories, GetFiles

Streams 

In .Net Framework input and output is done through streams.

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A stream is a continuous flow of bytes from a source to a destination.

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It could be memory to hard disk or from network to loc sys or one area of mem to another.

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An output stream is used when data is written to some external destination.

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Streams provide a way to write and read bytes to and from a storage medium.

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Streams hide the implementation details of input/output operations.

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A data channel having two ends, one is attached to the data source while the other is attached to the reader or writer of the data.

Streams..

Streams.. 

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Streams can be used for: 

Sequential file access Read from and write to the beginning of a file

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Random file access Read from and write to any locations within a file

Streams can be used to perform three fundamental operations: 

Read from a stream into a data type

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Write the contents of a data type to a stream

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Seek particular positions within a stream

Streams.. 

Different types of Streams are :

FileStreams – System.IO.FileStream

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MemoryStreams – System.IO.MemoryStream

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Networkstreams – System.Net.Sockets.NetworkStream

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System.IO.Stream is the base class for all stream classes in IO.

– Stream is an abstract class.

Streams.. 

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Different types of File Streams 

FileStream – read/write bytes to a file

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BinaryReader and BinaryWriter – To read/write primitive data types

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StreamReader and StreamWriter – To read/write text files

Stream Class Properties & Methods 

Length – returns long

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Position – returns long

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Flush(), Seek(long, SeekOrigin) (SeekOrigin.Begin, End, Current)

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ReadByte(Byte []ar, int offset, int count)

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WriteByte – same as readbyte

Streams 

File Modes - Enumeration FileMode 

Append If exists opens and seeks to the end of the file or creates a new file

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Create Create a new file, if exists overwrites

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CreateNew Create a new file, if exists throws IOException

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Open Opens an existing file, else throws FileNotFoundException

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OpenOrCreate If exists open or create a new one

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Truncate Opens an existing file and truncates to zero bytes

Streams 

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File Access 

Enum FileAccess

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Read, ReadWrite, Write

File Sharing 

Enum FileShare

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None – Declines sharing of the current file

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Read, ReadWrite, Write

FileMode, FileAccess and FileSharing to be specified in the FileStream constructors

Streams 

Binary Reader & Binary Writer 

What is the Disadvantages of FileStream?

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Parent class is only Object

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Can be used for read and writing primitive data types to and from files.

– Overloaded Read & Write methods to write all data types

Streams.. 

StreamReader and StreamWriter 

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Implements TextReader and TextWriter

StreamReader 

String ReadLine()

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ReadBlock(char[],int index, int count)

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String ReadToEnd()

StreamWriter 

Flush, Write(data type) – Overloaded methods, WriteLine(String)

Classes used for I/0 

File : A utility class that exposes many static methods for moving, copying and del files.

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Directory : A utility class that exposes many static methods for moving,copy and del directories.

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Path : A utility class that is used to manipulate path names.

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FileInfo: Represents phy file on disk, for read and writ a stream obj must be created.

Classes used for I/0 

DirectoryInfo : Represents a phy directory on disk.

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FileStream : both.

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SteamReader : Read char from a stream.

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StreamWriter : Writes char data to a stream

File that can be written or read or

File & Directory Classes File Class 

Copy()

-

Copies the file to specified location

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Create()

-

Creates a file in a specified path

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Delete()

-

Deletes a file

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Open()

-

Returns a FileStream object at the specified path

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Move()

-

Moves a specified file to specific location Directory Class

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CreateDirectory() - Creates a directory with the specified path

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Delete() within it

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GetDirectories() - Returns the array of Directory objects that represent the directories below the current directory

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Move()

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GetFiles directory

- Deletes the specified directory and all files

- Moves a specified directory to the new location - Returns an array of file objects in the current

FileInfo & DirectoryInfo Classes 

Attributes current file

- Gets or Sets the attributes of

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CreationTime current life

- Gets the creation date & time for

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DirectoryName - Returns the path to the file directory

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Exists

- Determine whether file exists

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Fullname current life

- Retrieves the full path of the

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Length

- Gets the size of file

File Stream Class 

It represents a stream pointing to a file on a disk or network path.

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FileStream class operates on bytes and byte arrays.

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Objects of FileStream class provide random access to files using the Seek() method.

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Seek() method allows read/write positions to be moved within a file.

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General structure of Seek() method is: Seek(byte_position, reference_ point) Example:

Seek(10, SeekOrigin.Begin);

Properties of Seek Origin 

SeekOrigin.Begin – Refers to the beginning of the file position

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SeekOrigin.Current – Refers to the current file position

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SeekOrigin.End – Refers to the end of the file position

File Stream Class Constructor 

Initializes a new instance of the FileStream object for the specified file

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The general structure of the constructor can be given as:

public FileStream(path, FileMode, FileAccess); In this code, 

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path – Represents the file name or file path FileMode – Determines how the file is opened or created FileAccess – Determines how the file may be accessed by the FileStream object

File Stream 

File Mode Property Values

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File Access Property Values

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Append

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Read

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Create

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Write

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CreateNew

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ReadWrite

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Open

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OpenOrCreate

Creating File Stream Object FileStream fs= new FileStream(“Myfile.txt”, FileMode.Append, FileAccess. Write);

This opens the file, Myfile.txt , in the append mode for the write operation.

Example – File Stream using System; using System.IO; namespace Files { class Class1 { static void Main(string[] args) { string str; try { FileStream fs =

new FileStream(@"c:\newfile.xls", FileMode.OpenOrCreate);

Example – File Stream

StreamWriter sw = new StreamWriter(fs); sw.WriteLine("hi"); sw.WriteLine("Welcome to filehandling classes"); sw.Close(); } catch (IOException e) { Console.WriteLine("An IO exception Occurred " + e); }

Example – File Stream StreamReader sr = new StreamReader(@"c:\newfile.txt"); str = sr.ReadToEnd(); while (str != null) { Console.WriteLine(str); str = sr.ReadLine(); } sr.Close(); } } }

Stream Writer 

The objects of StreamWriter class are used to perform write operations to a stream.

Example: StreamWriter sw=new StreamWriter(fs); In this code, fs is an object of the stream class.

Example – Stream Writer using System; using System.IO; namespace day8 { class Class1 { static void Main(string[] args) { try { FileStream fs = new FileStream(@"d:\log.txt", FileMode.OpenOrCreate);

Example – Stream Writer.. StreamWriter sw = new StreamWriter(fs); sw.WriteLine("hi, how are you"); sw.WriteLine("This is string"); sw.Close(); } catch (IOException e) { Console.WriteLine("An IO exception Occurred " + e); } } } }

Stream Reader 

Objects of the StreamReader class is used to perform read operations from a stream.

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Example:

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In the above code, fs is an object of the stream class.

StreamReader sr=new StreamReader(fs);

Example – Stream Reader using System; using System.IO; namespace day8 { class Class1 { static void Main(string[] args) { string str; try { FileStream fs = new FileStream(@"d:\log.txt", FileMode.Open); StreamReader sr = new StreamReader(fs); str = sr.ReadLine();

Example – Stream Reader while (str != null) { Console.WriteLine(str); }

str = sr.ReadLine();

sr.Close(); } catch (IOException e) { Console.WriteLine("Sorry!.Exception Occurred " + e.ToString());

}

}

}

}

Random Access 

Reading data using File Stream class is not as easy the StreamReader class because it deals exclusively with Raw bytes.

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Read from and write to any locations within a file is called Random Access.

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This class is used to read files such as images and sounds. For reading strings with FileStream class we have to use conversion classes to convert byte data into character form.

Example – Random Access using System; using System.IO; using System.Text; namespace Files { public class Randomaccess { static byte[] bdata = new byte[1000]; static char[] cdata = new char[1000]; static void writing() { try { FileStream fs =

new FileStream(@"c:\rndfile1.txt", FileMode.OpenOrCreate);

cdata = "hello how are you??".ToCharArray();

Example – Random Access Encoder e = Encoding.UTF8.GetEncoder(); e.GetBytes(cdata, 0, cdata.Length, bdata, 0, true); fs.Seek(0, SeekOrigin.Begin); fs.Write(bdata, 0, bdata.Length); fs.Flush(); } catch (IOException e) { Console.WriteLine("An IO exception occurred" + e); } }

Example – Random Access static void reading() { try { FileStream fs = new FileStream(@"c:\rndfile1.txt", FileMode.Open); //cdata = "hello ".ToCharArray (); //e.GetBytes (cdata,0,cdata.Length ,bdata,0,true); fs.Seek(0, SeekOrigin.Begin); fs.Read(bdata, 0, 10);

} catch (IOException e) { Console.WriteLine("An IO exception occurred" + e); return; }

Example – Random Access static void Main() { //writing(); //Console.WriteLine("writing completed"); Console.WriteLine("data written in the file:"); reading(); }

}

}

Asynchronous File Access 

Flow of application did not continue until the read or write operation is completed is called Synchronous operation.

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Suppose when you need to write large chunk of data but we don't need the application to wait for it to complete before continuing or we need to read from a file on a network location with slow connection, our application can continue to do other processing is called Asynchronous operation.

Example – Asynchronous File Access using System; using System.IO; using System.Text; namespace Files { public class Asynchronousaccess { static byte[] bdata = new byte[1000]; static char[] cdata = new char[1000]; static void writing() { try { FileStream fs = new FileStream(@"c:\C#\asyfile1.cs", FileMode.Open);

Example – Asynchronous File Access fs.Seek(0, SeekOrigin.Begin); System.IAsyncResult synchResult = fs.BeginRead(bytedata, 0,100,null,null); //Do other processing while data is being read while(!synchResult.IsCompleted) { Console.WriteLine(“Reading from file”); }

fs.EndRead(synchResult);

Decoder d = Encoding.ASCII.GetDecoder(); d.GetChars(bytedata,0,bytedata.Length,chardata,0); Console.Write(chardata); }

Example – Asynchronous File Access catch(IOException e) { Console.WriteLine(“Exception Occurred”+e.ToString()); } }

}

}

Multi Tasking & MultiThreading 

MultiTasking 

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Different applications execute at the same time

MultiThreading 

One application has more than one application path at the same time

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Namespace to be included Using System.Threading

MultiThreading 

Creating a Thread 

A Thread in .Net is represented by a System.Threading.Thread class

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Multiple threads are nothing but multiple instances of this object

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The method to be called when a thread starts is to be specified by passing a delegate of the ThreadStart type to the Thread’s constructor.

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The method should return void and not take any parameters.

MultiThreading.. 

A thread to be started using the Start method of the Thread class.

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Methods of Thread class 

Thread.Sleep(int time in milliseconds)

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Name (Property to get/set a thread’s name)

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IsAlive(Property to find whether a thread is alive or not)

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ThreadState (Property – Aborted, Stopped, Running, Suspended, Unstarted etc)

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Priority – (Property to set/get the priority of a thread)

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Start

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Abort

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Suspend

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Resume

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Join

MultiThreading.. 

Thread Priorities – Normal, AboveNormal, BelowNormal, Highest and Lowest – Default priority is Normal – To change the priority » secondThread.Priority = ThreadPriority.AboveNormal;

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When a thread is aborted a ThreadAbortException is thrown.

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Calling Suspend(), Resume() or Abort() methods on a non-running thread a ThreadStateException is thrown

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Thread Synchronization – .Net provides a locking mechanism to avoid simultaneous access by multiple threads to the same shared object.

Session Ends

Exercise

Relax