1. Object Oriented Programming
Files and Streams
Dr. Mike Spann

2. Contents Introduction Sequential file I/O Classes File and Directory
Serialization
Summary

3. Introduction Most applications require data to be stored in files
Spreadsheets
Word processing
etc
C# has an extensive set of classes for handling files of various types
These are to be found in the System.IO namespace
Associated with files is the general concept of streams which can be applied to both files and networks

4. Introduction In C#, streams are simply sequences of bytes
No formattng structure is placed on this byte stream, this is imposed by the appliction
We can read a byte stream from an input stream object
We can write a byte stream to an output stream object
The input and output stream objects are created from class FileStream

5. Introduction FileStream object byte stream FileStream object

6. Sequential file I/O
There are many classes in the FCL for file handling
FileStream is the basic file for handling I/O from binary files
The constructor opens a stream object and specifies the filename and file access (read, write etc)
It provides a Read() and Write() method
Its normal to enclose file handling code in a try{} catch{} clause to catch any exceptions thrown

7. Sequential file I/O using System; using System.IO; class FileCopy {
class FileCopy {
public static void Main(String[] args){
try{
FileStream fromStream =
new FileStream(args[0], FileMode.Open, FileAccess.Read);
FileStream toStream =
new FileStream(args[1], FileMode.Create, FileAccess.Write);
Byte[] buffer = new Byte[fromStream.Length];
fromStream.Read(buffer, 0, buffer.Length);
toStream.Write(buffer, 0, buffer.Length);
}catch{
Console.WriteLine("Usage: FileCopy [FromFile] [ToFile]"); }

8. Sequential file I/O
FileStream.Read() and FileStream.Write() are for binary files
Data is stored in files as bytes which is efficient but not humanly readable
A text file consists of information stored in humanly readable form
For example the number 150 would be stored as ‘1’ ‘5’ ‘0’ instead of the binary representation of 150 ( )
C# has a number of classes (descended from the abstract TextReader and TextWriter classes) for handling text i/o

9. Sequential file I/O
For text files, classes StreamReader and StreamWriter are provided
These are derived from TextReader and TextWriter
They use the familiar ReadLine() and WriteLine() methods for doing formatted I/O
Note that the Console class has StreamReader and StreamWriter objects and uses their ReadLine() and WriteLine() methods for doing console-based I/O

10. using System;
using System.IO;
class CreateTextFile {
public static void Main(String[] args)
try
FileStream toStream =
new FileStream(args[0], FileMode.Create, FileAccess.Write);
StreamWriter fileWriter = new StreamWriter(toStream);
for (int i = 0; i < 10; i++)
fileWriter.WriteLine("i= " + i);
fileWriter.Close();
toStream.Close();
FileStream fromStream =
new FileStream(args[0], FileMode.Open, FileAccess.Read);
StreamReader fileReader = new StreamReader(fromStream);
String input = fileReader.ReadLine();
Console.WriteLine(input); }
catch{Console.WriteLine("Usage: CreateTextFile OutputFile");

11. Sequential file I/O

12. Classes File and Directory
Classes File and Directory allow an application to obtain information about files and directories stored on disc
Each class contains a large set of static methods for both manipulation and information gathering
These classes could be the basis of a hard disc scanning application to determine usage and the amount of available storage space

13. Classes File and Directory

14. Classes File and Directory

15. Classes File and Directory

16. Classes File and Directory
As a simple example, we can use an OpenFileDialog box (which only allows files to be selected) or a FolderBrowserDialog
We can then use the File or Directory classes to print information about the selected item
For a file we print the file size and last modified date
For a directory, we print its contents

18. using System;
using System.Windows.Forms;
using System.IO;
public partial class FileTestForm1 : Form {
public FileTestForm1()
{ InitializeComponent(); }
private void openFileDialog1_FileOk(object sender, CancelEventArgs e)
string fileName = openFileDialog1.FileName;
if (File.Exists(fileName))
displayFileInfo(fileName); }
private void displayFileInfo(string fileName)
{ // Displays file information }
private void displayDirectoryInfo(string pathName)
{ // Displays directory information }
private void button1_Click(object sender, EventArgs e)
{ openFileDialog1.ShowDialog(); }
private void button2_Click(object sender, EventArgs e)
folderBrowserDialog1.ShowDialog();
string pathName = folderBrowserDialog1.SelectedPath;
if (Directory.Exists(pathName))
displayDirectoryInfo(pathName);

19. Classes File and Directory
private void displayFileInfo(string fileName) {
outputTextBox.Text += "\r\n\r\nFile: " + fileName + ":\r\n";
DateTime creationTime = File.GetCreationTime(fileName);
outputTextBox.Text += "Created: " + creationTime.ToString() + "\r\n";
DateTime lastModifiedTime = File.GetLastAccessTime(fileName);
outputTextBox.Text += "Last accessed: " + lastModifiedTime.ToString() + "\r\n"; }
private void displayDirectoryInfo(string pathName)
string[] directoryList;
directoryList = Directory.GetDirectories(pathName);
outputTextBox.Text += "\r\n\r\nDirectory Contents:\r\n";
// Output directory contents
for (int i = 0; i < directoryList.Length; i++)
outputTextBox.Text += directoryList[i] + "\r\n";

20. Classes File and Directory
Demos\Files and Streams\FileTestForm.exe

21. Serialization
It is easy to write the individual fields of a record object to a file
For example, we can create a record that stores information about a student
Name
Address
ID number
Course enrolled for
etc
We can output each field of this record to a file (either text or binary)

22. Serialization Record file StudentInfo Name Address ID number
string string int string
StudentInfo
Name
Address
ID number
Course Info

23. Serialization
In this example, any program that needs to read the file needs to know the format of the data
2 strings, an int and then a string
Also whether each item is on a separate line
Object serialization allows complete objects to be read or written with a single statement
A serialized object is an object represented as a sequence of bytes
Information is stored about the data types of the objects instance fields as well as their values
Allows the object to be reconstructed (de-serialized) from the file

24. Serialization Record file StudentInfo Name Address ID number
StudentInfo object
StudentInfo
Name
Address
ID number
Course Info

25. Serialization
To serialize an object, the object class needs to be marked with the [Serializable] attribute or needs to implement the ISerializable interface
Requires the System.Runtime.Serialization namespace
Also we require a BinaryFormatter object to serialize/de-serialize the object before writing to or reading from file
It’s also possible to serialize objects using SOAP (simple object access protocol) or xml using the appropriate formatters

26. Serialization
Example. A custom serializer GUI

27. Serialization
The user inputs student info. details in the corresponding textboxes on the left which through the serialization will be stored in a binary file
The information in the binary file will be deserialized and displayed in the right hand textboxes
We will create a simple StudentInfo class and tag it as Serializable

28. Serialization [Serializable] class StudentInfo {
public string Name, Address, CourseInfo;
public int ID;
public StudentInfo() {}
public StudentInfo(String n, String a, String ci, int id)
Name = n; Address = a; CourseInfo = ci;
ID = id; }

29. Serialization using System.Windows.Forms; using System.IO;
using System.Runtime.Serialization;
using System.Runtime.Serialization.Formatters.Binary;
public partial class SerializerTestForm1 : Form {
private String fileName = Directory.GetCurrentDirectory() "\\output1.txt";
public SerializerTestForm1()
InitializeComponent(); }
private void button1_Click(object sender, EventArgs e)
//Serialize textbox data to a binary file
private void button2_Click(object sender, EventArgs e)
//De-Serialize a binary data back to textbox data

30. Serialization private void button1_Click(object sender, EventArgs e) {
button1.Enabled = false;
String name = textBox1.Text;
String address = textBox2.Text;
int id = Convert.ToInt32(textBox3.Text);
String courseInfo = textBox4.Text;
StudentInfo s = new StudentInfo(name,address,courseInfo,id);
FileStream filestream = new FileStream(fileName, FileMode.Create);
BinaryFormatter bf = new BinaryFormatter();
bf.Serialize(filestream, s);
filestream.Close();
button1.Enabled = true; }
private void button2_Click(object sender, EventArgs e)
FileStream filestream2 = new FileStream(fileName,FileMode.Open);
BinaryFormatter bf2 = new BinaryFormatter();
StudentInfo si= new StudentInfo();
si = (StudentInfo)bf2.Deserialize(filestream2);
textBox8.Text = si.Name;
textBox7.Text = si.Address;
textBox6.Text = ""+si.ID;
textBox5.Text = si.CourseInfo;
filestream2.Close();

31. Serialization
Demos\Files and Streams\SerializerTestForm.exe

32. Serialization

33. Serialization
Binary serialization is limited as only .NET applications can deserialize the data stream
For more general inter-operability especially across a network, xml serialization is used
xml is text based and self descibing and universal
Comprised name/attribute pairs
xml serialization easy to implement and uses text streams

34. Serialization We need to insert xml tags into our StudentInfo class
Only public properties and fields can be serialized
[XmlRoot("studentInfo")]
public class StudentInfo {
[XmlAttribute("name")] public string Name;
[XmlAttribute("address")] public string Address;
[XmlAttribute("course")] public string CourseInfo;
[XmlAttribute("id")] public int ID;
public StudentInfo()
{ }
public StudentInfo(String n, String a, String ci, int id)
Name = n; Address = a; CourseInfo = ci;
ID = id; }

35. using System;
using System.Windows.Forms;
using System.IO;
using System.Xml;
using System.Xml.Serialization;
public partial class xmlSerializerTestForm1 : Form {
private String fileName = Directory.GetCurrentDirectory() + "\\output1.xml";
public xmlSerializerTestForm1() {InitializeComponent();}
private void button1_Click(object sender, EventArgs e)
button1.Enabled = false;
String name = textBox1.Text;
String address = textBox2.Text;
int id = Convert.ToInt32(textBox3.Text);
String courseInfo = textBox4.Text;
StudentInfo si = new StudentInfo(name, address, courseInfo, id);
XmlSerializer xmls = new XmlSerializer(typeof(StudentInfo));
TextWriter w = new StreamWriter(fileName);
xmls.Serialize(w, si);
w.Close();
button1.Enabled = true; }
private void button2_Click(object sender, EventArgs e)
StudentInfo si;
TextReader r = new StreamReader(fileName);
si = (StudentInfo)xmls.Deserialize(r);
textBox8.Text = si.Name;
textBox7.Text = si.Address;
textBox6.Text = "" + si.ID;
textBox5.Text = si.CourseInfo;
r.Close();

36. Serialization

37. Summary
We have seen how we can use streams to do simple sequential file I/O for binary and text files
We have looked at how we can use the File and Directory classes
We have looked at object serialization to binary and xml