1. C# - Files and Streams
Outline Files and Streams Classes File and Directory Creating a Sequential-Access File Reading Data from a Sequential-Access File

2. Files and Streams When file opened C#:
Creates an object
Associates a stream with that object
Three stream objects:
Console.In: returns standard input stream object
Console.Out: returns standard output stream object
Console.Error: returns standard error stream object
Namespace System.IO needed for file processing

3. Files and Streams
System.IO.Stream: allows representation of stream as bits
FileStream: read to and write from sequential- access and random-access files
MemoryStream:transfer of data directly to and from memory
BufferedStream: uses buffer to transfer to memory

4. Classes File and Directory
Information stored in files
Files organized in directories
Directory class used to manipulate directories
File class used to manipulate files
Only has static methods, cannot instantiate File objects

5. // get user-specified file or directory string fileName = ???
// determine whether fileName is a file
if ( File.Exists( fileName ) ) {
// obtain reader and file contents
try
{ StreamReader stream = new StreamReader( fileName );
string inputString = stream.ReadToEnd(); }
// handle exception if StreamReader is unavailable
catch( IOException )
{ MessageBox.Show( "File Error", "File Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
Set fileName to what user typed
See if fileName is an existing file
Create StreamReader to read text from file
Call method ReadToEnd

6. else {
// notify user that neither file nor directory exists
MessageBox.Show( filename + " does not exist", "File Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); }
} // end if
FileTest.cs
If user input is not existing file output error message

7. SaveFileDialog

8. SaveFileDialog fileChooser = new SaveFileDialog();
// create dialog box enabling user to save file
SaveFileDialog fileChooser = new SaveFileDialog();
DialogResult result = fileChooser.ShowDialog();
// allow user to create file
fileChooser.CheckFileExists = false;
// exit event handler if user clicked "Cancel“
if ( result != DialogResult.Cancel )
{ // get specified file name
string fileName = fileChooser.FileName;
// show error if user specified invalid file
if ( fileName == "" || fileName == null )
MessageBox.Show( "Invalid File Name", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
Instantiate SaveFileDialog object
Show SaveFileDialog
Test if user canceled save
Get file name to save to

9. // save file via FileStream if user specified valid file try
else {
// save file via FileStream if user specified valid file
try
// open file with write access
output = new FileStream( fileName, FileMode.OpenOrCreate, FileAccess.Write ); }
// notify user if file does not exist
catch ( FileNotFoundException )
MessageBox.Show( "File Does Not Exist", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
Instantiate output stream with write permission
Method to save data when user clicks enter

10. Creating or Writing to a Sequential-Access File
Programmers have to structure files to meet the requirements of applications
Declare and define a record class which describes the structure of the data
Write the main class to write out a record

11. Libraries Needed to read a file sequentially
using System;
using System.IO;
using System.Runtime.Serialization.Formatters.Binary;
using System.Runtime.Serialization;

12. // set members to default values
[Serializable]
public class Record
{ private int account;
private string firstName;
private string lastName;
private double balance;
// set members to default values
public Record() : this( 0, "", "", 0.0 )
{ }
Tells compiler objects of class Record can be represented as a set of bytes
Data to go into record
Sets members to 0

13. // set members to parameter values
public Record( int accountValue, string firstNameValue,
string lastNameValue, double balanceValue ) {
Account = accountValue;
FirstName = firstNameValue;
LastName = lastNameValue;
Balance = balanceValue;
} // end constructor
Set members to parameters

14. Record.cs // property Account public int Account { get
{ return account; }
set
{ account = value; }
} // end property Account
} //end class
Record.cs
Other properties and methods

15. Main class
// Creating a sequential-access file of records // C# namespaces using System.IO; using System.Runtime.Serialization.Formatters.Binary; using System.Runtime.Serialization; // serializes Record in binary format private BinaryFormatter formatter = new BinaryFormatter(); // stream through which serializable data is written to file private FileStream output;

16. formatter.Serialize( output, record );
// Record containing TextBox values to serialize
Record record = new Record();
// store values in Record and serialize Record
try {
record.Account = Int32.Parse(
values[ ( int )TextBoxIndices.ACCOUNT ] );
record.FirstName = values[ ( int )TextBoxIndices.FIRST ];
record.LastName = values[ ( int )TextBoxIndices.LAST ];
record.Balance = Double.Parse( values[ ( int )TextBoxIndices.BALANCE ] );
// write Record to FileStream (serialize object)
formatter.Serialize( output, record ); }
Store TextBox fields in record
Write data to file

17. // notify user if error occurs in serialization
catch( SerializationException ) {
MessageBox.Show( "Error Writing to File", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error ); }
// notify user if error occurs regarding parameter format
catch( FormatException )
MessageBox.Show( "Invalid Format", "Error",
Catch block if user input invalid data
Close FileStream

18. Don’t forget to close the output file!
// invoked when user clicks Exit button
private void exitButton_Click( object sender, System.EventArgs e ) {
// determine whether file exists
if ( output != null )
// close file
try
output.Close(); }

19. Reading Data from a Sequential-Access File
Read data sequentially from a file
Programs usually start at beginning of file and read data consecutively until the desired data is found
Sometimes necessary to do this several times during execution of a program
File-position pointer:
Points to next byte to be read from or written to file
Can be repositioned to any point in file

20. private void openButton_Click( object sender, System.EventArgs e ) {
// invoked when user clicks Open File button
private void openButton_Click(
object sender, System.EventArgs e ) {
// create dialog box enabling user to open file
OpenFileDialog fileChooser = new OpenFileDialog();
DialogResult result = fileChooser.ShowDialog();
// exit event handler if user clicked Cancel
if ( result != DialogResult.Cancel )
{ // get name from user
fileName = fileChooser.FileName;
// show error if user specified invalid file
if ( fileName == "" || fileName == null )
MessageBox.Show( "Invalid File Name", "Error",
MessageBoxButtons.OK, MessageBoxIcon.Error );
User clicked open button
Instantiate OpenFileDialog
Show OpenFileDialog

21. 87
// read and display file information
try {
// close file from previous operation
if ( input != null )
input.Close(); 94
// create FileStream to obtain read access to file
input = new FileStream( fileName, FileMode.Open, FileAccess.Read );

22. 101 // traverse file until end of file 102 while ( true ) 103 { {
// get next Record available in file
Record record = ( Record )reader.Deserialize( input );
// display record
string output = record.Account + "\t" +
record.FirstName + "\t" + record.LastName +
new string( ' ', 6 ) + "\t";
117
// display balance with correct monetary format
output += String.Format(
"{0:F}", balance ) + "\r\n";
121
// copy output to screen
displayTextBox.Text += output; }
While loop to read from file
Read input from file

23. // handle exception when no more records {
catch( SerializationException ) {
// close FileStream if no Records in file
input.Close(); }
No more records exception
Close FileStream