1. CSCI 3328 Object Oriented Programming in C# Chapter 11: Files and Streams
UTPA – Fall 2012
This set of slides is revised from lecture slides of Prof. John Abraham. -- Xiang Lian

2. Objectives In this chapter, you will
Learn how to create, read, write, and update files
Know how to use classes File and Directory to obtain information about files and directories on your computer
Learn how to use LINQ to search through directories
Get familiar with sequential-access file processing
Know how to use classes FileStream, StreamReader, StreamWriter, FileStream, and BinaryFormatter, as well as yield return

3. Introduction Variables and arrays only offer temporary storage of data
Data are lost when the program terminates
In contrast, files are used for long-term storage place
Persistent data
Data are stored on secondary storage devices

4. Data Hierarchy Bits Characters (ASCII or Unicode) Fields Records Files
Record key
Sequential file
Databases

5. Files and Streams File as a sequential stream of bytes
Each file ends with an end-of-file marker
Windows keeps track of total number of bytes in a file
When a file is opened an object is created and a stream is associated with the object
Each program automatically gets 3 objects, Console.Out, Console.In and Console.Error

6. Classes File and Directory
Files are organized in directories
Class Directory provides capabilities for manipulating directories
Class File has static methods:
AppendText, Copy, Create, CreateText, Delete, Exists, GetCreationTime, GetLastAccessTime, GetLastWriteTime, Move, Open, OpenRead, OpenText, OpenWrite

7. Directory Class Static Methods
CreateDirectory
Delete
Exists
GetDirectories
GetFiles
GetCreationTime
GetLastAccessTime
GetLastWriteTime
Move

8. Create a File to Read/Write
Pre-defined class library
using System.IO;
StreamWriter (for text output)
StreamWriter outFile = new StreamWriter(fileName);
StreamReader (for text input)
StreamReader inFile = null;
try{
using (inFile = new StreamReader(fileName))
{ outputTextBox.AppendText(inFile.ReadToEnd());}
} catch(IOException) {
MessageBox.Show("Error reading from file", "File Error", MessageBoxButton.OK, MessageBoxIcon.Error); }

9. Write to the File string fileName="test.txt"; File.Exists(fileName)
true, if fileName exists
outFile.WriteLine("text");
Other methods
File.GetCreationTime(fileName);
File.GetLastWriteTime(fileName);
File.GetLastAccessTime(fileName);

10. Read From the File
inFile.ReadLine("text");

11. Close the File
outFile.Close();
inFile.Close();

12. Directory Directory.Exists(Name);
true, if directory Name exists
string [] directoryList = Directory.GetDirectories(Name);
Obtain a list of files and directories

13. Searching Directories with LINQ
string currentDirectory;
currentDirectory = Directory.GetCurrentDirectory();
string [] files = Directory.GetFiles(currentDirectory);
string [] directories=Directory.GetDirectories(currentDirectory);
var extensions = (from file in files
select Path.GetExtension(file)).Distinct();
foreach(var extension in extensions) {
var extensionCount = (from file in files
where Path.GetExtension(file)==extension
select file).Count(); }

14. Dictionary Class A class Dictionary is a collection of key/value pairs
In namespace System.Collections.Generic
Dictionary <string, int> found = new Dictionary <string, int>();
Key is of string data type, and value is of int data type
Methods
found.ContainsKey(extension)
true, if the directory contains a key for the extension
found.Add(extension, extensionCount);
found[extension]
Returns the value of the key "extension"
found.Keys
A collection of keys

15. Example of Deleting Files
var backupFiles = from file in files
where Path.GetExtension(file)==".bak"
select file;
foreach (var backup in backupFiles) {
DialogResult result = MessageBox.Show("Found backup file "
+ Path.GetFileName(backup) + ". Delete?", "Delete Backup", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
if (result == DialogResult.Yes)
File.Delete(backup); // delete the file with name in "backup"
found[".bak"]--; // decrement the counter
if (found[".bak"] == 0)
found.Remove(".bak"); // remove the key from dictionary }

16. Create a Sequential File
In C# files, the concept of a "record" does not exist
Therefore, you have to create structured files by yourself
Use text and special characters to separate fields in the record
public enum TextBoxIndices // enumeration {
ACCOUNT,
FIRST,
LAST,
BALANCE }

17. Example of Creating a Sequential File
public class Record { public int Account {get; set;} public string FirstName {get; set;} public string LastName {get; set;} public decimal Balance {get; set;} public Record() :this(0, string.Empty, string.Empty, 0M){} public RecordSerializable (int acc, string fName, string lName, decimal bal) Account = acc; FirstName = fName; LastName = lName; Balance = bal; }

18. Example of Creating a Sequential File (cont'd)
FileStream output = new FileStream (fileName, FileMode.OpenOrCreate, FileAccess.Write);
StreamWriter fileWriter = new StreamWriter(output);
Record record = new Record();
fileWriter.WriteLine(record.Account + ","
+ record.FirstName + ","
+ record.LastName + ","
+ record.Balance);

19. Reading Data From a Sequential-Access Text File
FileStream input = new FileStream(fileName, FileMode.Open, FileAccess.Read);
StreamReader fileReader = new StreamReader(input);
string inputRecord = fileReader.ReadLine();
string[] inputFields;
if (inputRecord != null) {
inputFields = inputRecord.Split(',');
Record record = new Record(Convert.ToInt32(inputFields[0]), inputFields[1], inputFields[2],
Convert.ToDecimal(inputFields[3])); }

20. Class BinaryFormatter
Under namespace System.Runtime.Serialization.Formatters.Binary
Serializable(outFile, object) method
Write a serializable object to the output file
Serialization
In a class that is marked with [Serializable] attribute or that implements interface Iserializable, you must ensure that every instance variable in a class is also serializable
All simple-type variables, strings, and arrays (without containing references) are serializable

21. Example of RecordSerializable Class
public class RecordSerializable { [Serializable] public int Account {get; set;} public string FirstName {get; set;} public string LastName {get; set;} public decimal Balance {get; set;} public RecordSerializable() :this(0, string.Empty, string.Empty, 0M){} public RecordSerializable (int acc, string fName, string lName, decimal bal) Account = acc; FirstName = fName; LastName = lName; Balance = bal; }

22. Example of RecordSerializable Class (cont'd)
BinaryFormatter formatter = new BinaryFormatter(); FileStream output = new FileStream(fileName, FileMode.OpenOrCreate, FileAccess.Write); try{ RecordSerializable record = new RecordSerializable(); formatter.Serialize(output, record); } catch (SerializationException) { // … catch (FormatException)

23. Reading and Deserializing Data From a Binary File
BinaryFormatter reader = new BinaryFormatter();
FileStream input = new FileStream(fileName, FileMode.Open, FileAccess.Read);
try{
RecordSerializable record = (RecordSerializable) reader.Deserialize(input); }
catch (SerializationException) {
input.Close();

24. Select Files from Chooser
Recall this topic in lecture slides of Chapter 8

25. Obtaining File Name From Chooser
OpenFileDialog fDialog = new OpenFileDialog();
if (fDialog.ShowDialog() == DialogResult.OK) {
fileName = (fDialog.FileName.ToString());
MessageBox.Show(fileName); }

26. Reading From a File StreamReader ofile = new StreamReader(fileName);
while (ofile.Peek()!=-1) {
string oneline = ofile.ReadLine();
MessageBox.Show(oneline,"Reading From File..");
string[] items = oneline.Split(',');
onePerson.fName = items[0];
onePerson.lName = items[1];
onePerson.GPA = Convert.ToSingle(items[3]);
onePerson.Tele = items[2];
friendsList.Add(onePerson); }
ofile.Close();

27. Writing to the File StreamWriter outfile = new StreamWriter(fileName);
foreach (Info person in friendsList)
outfile.WriteLine(person.fName+","+person.lName+","+person.Tele+","+Convert.ToString(person.GPA));
outfile.Close();