Visual C Sharp – File I/O - 1 Variables and arrays only temporary - lost when a program terminates Files used for long term storage (Data bases considered.

Visual C Sharp – File I/O - 1

Variables and arrays only temporary

- lost when a program terminates

Files used for long term storage

(Data bases considered later in course)

We will cover: File types File and Directory classes File open and save dialogs Sequential-access files Random-access files Stream-input/output features


File Types – Text (ASCII) or Binary

Text files - ASCII characters with CR and LF.

Handled in a line-by-line, or sequential manner.

Binary Files - Typed and Untyped filesBinary files all values - can’t be displayed - .EXE file.

Typed files - known format using data types - database. Untyped files - no rigid structure, sizes can vary.

E.g. EXE program files, BMP bitmap graphic files.

- Program using it knows how to deal with it.


Files and streamsC# views files as a sequential stream of bytes.

File ends with EOF marker or after a byte count.

You open the file, read and write to it, then close it.

Uses StreamReader and StreamWriter Classes

They implement methods to read and write files.

Similar classes used to read/write to Internet or serial I/O


File and Directory Classes (static classes) Can perform Directory or File handling:Directory:

CreateDirectory, Delete, GetFiles, ExistsFile:

Exists – does file exist?Create – creates file CreateText – creates a text fileAppendText – appends or createsDelete – deletes the fileOpen – opens with desired R / W attributesOpenRead – opens for read-onlyOpenText – returns StreamReader (later)OpenWrite – returns FileStream (later)

Need ‘using System.IO’


First of all – Menu and Dialog controls

Text Editor exampleMenuStrip control used to create menus (File Edit Help)

C# has FileDialog controls open and save files

– OpenFileDialog & SaveFileDialog

Rich Text box control will display text files

RT box has more functions than textbox – cut, paste etc.


File Dialog controlsOpen and Save dialogs

– non visual (not on form – appear when program runs)

ShowDialog displays the familiar open and save dialogs:

Visual C Sharp – File I/O - 7MenuStrip control:Enter required main menu commands (File, Edit, Help)

Add submenus: File>Open, Help > About etc.

To add code – click File’, double-click ‘Open’ Add code: if (openFileDialog1.ShowDialog( ) != DialogResult.Cancel) {

richTextBox1.LoadFile(openFileDialog1.FileName, RichTextBoxStreamType.PlainText); // more detail later

}

ShowDialog method displays the familiar file handling dialog

Visual C Sharp – File I/O - 8Code to display FileDialogs. Use:

openFileDialog1.ShowDialog( ) and saveFileDialog1.ShowDialog( )

Need to check for OK or Cancel.

if (openFileDialog1.ShowDialog( ) != DialogResult.Cancel) { // filename is: openFileDialog1.FileName }

N.b.File I/O needs namespace: using System.IO

Visual C Sharp – File I/O - 9Open/Save File dialog properties:CheckFileExists’, ‘DefaultExt’ InitialDirectory etc.

File filter. Can set in code:openFileDialog1.Filter = "All files (*.*)|*.*|Text files(*.TXT)|*.txt";


Rich Text Box file handlingEasiest way to open and save text files is to use RTB

Open file:

if (openFileDialog1.ShowDialog() != DialogResult.Cancel)

{ richTextBox1.LoadFile(openFileDialog1.FileName, RichTextBoxStreamType.PlainText); }

RTB has methods, e.g:RTB.Find method – finds strings in RTB (Search)


Rich Text Box file handling – Save file

For MenuStrip File>Save, add:

if (saveFileDialog1.ShowDialog( ) != DialogResult.Cancel)

{

RichTextBox1.SaveFile(saveFileDialog1.FileName,

RichTextBoxStreamType.PlainText);

}

Text editor created in a few lines of code.


Using StreamReader to read file into RichTextBox:

StreamReader streamRdr = new StreamReader(openFileDialog1.FileName); richTextBox1.Text = streamRdr.ReadToEnd( ); streamRdr.Close( );

Writing file using StreamWriter

StreamWriter streamWr = newStreamWriter(saveFileDialog1.FileName);

streamWr.Write(richTextBox1.Text) streamWr.Close( );

Why use? – may not want to use RT box to read file


Example code snippet – read file:

string filename;

filename = txtFilename.Text; // read from textbox

if ( File.Exists(filename) )

{

string inputString = File.ReadAllText(fileName);

textBox1.Text = inputString;

}


Example code snippet - write:

string filename;

filename = txtFilename.Text; // read from textbox

if ( File.Exists(filename) )

{

File.WriteAllText(filename, txtFileName.txt);

textBox1.Text = inputString;

}


File class methods:

AppendText - Returns a StreamWriter which appends to a file or creates a new file.

Create - Creates a file and returns FileStream.

CreateText - Creates a text file and returns a StreamWriter.

Delete - Deletes the specified file

Open - Opens a file and returns a FileStream with specified read/write permission.

OpenText - Returns a StreamReader associated with the specified file.


Binary files:// Read:

byte[] fileByteArray = new byte[1000];

fileByteArray = File.ReadAllBytes("test.bin");

// have to do something with the binary files to display them

// could split into upper and lower ‘nibbles’ and add 40hex

// makes chars @ABC.. MNO

// To Write:

File.WriteAllBytes("test.bin", fileByteArray);


Sequential-Access File HandlingNon-text files? E.g. Student record (integer, string, double)

Could create our own Record, Class, or even object for this.

Search - Start at beginning and read data until its found• Maybe necessary to do this lots of times

Tell compiler our Class can be saved as bytes – ‘Serializable’ attribute

FileStream class used to writing of binary data

(instead of StreamReader/Writer)

Visual C Sharp – File I/O - 18Random Access File HandlingAllows instant access to information- Individual records accessed without searching through file

Easiest when all records are a fixed lengthData can be inserted without destroying other data in fileRecords can be updated without rewriting the entire fileUses file-position pointer - points to next byte to be read or written - can be repositioned to any point in file

Uses class BinaryWriter and BinaryReader instead of serializationBy attaching a FileStream to it, bytes can be read/written directly to a file


Exception handlingExceptions: File may not exist, divide by zero, convert alpha string to number

Use Try .. Catch codeint number1=123, zero = 0; try { number1 = number1 / zero; } catch (DivideByZeroException) { MessageBox.Show("Something's wrong here"); }


Summary File types MenuStrip control Text Editor example – RTBox Open / Save Dialogs Files and Streams Sequential-access files Random-access files

Visual C Sharp – File I/O - 1 Variables and arrays only temporary - lost when a program terminates Files used for long term storage (Data bases considered.

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