1. File I/O 11_file_processing.ppt
CIS162AD - C#
File I/O
11_file_processing.ppt

2. Overview of Topics Information Processing Cycle File Processing (I/O)
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3. Hardware Model CPU Input Devices Memory (RAM) Output Devices
Storage Devices
To this point we have been using the text boxes for input and picture boxes for output. Both of these are temporary.
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4. Information Processing Cycle
Input Raw Data
Process (Application)
Output Information
Storage
Output from one process can serve as input to another process.
Storage is referred to as secondary storage, and it is permanent storage. Data is permanently stored in files.
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5. Input and Output (I/O)
In the prior assignments, we would enter the test data and check the results.
If it was incorrect, we would change the program, run it again, and reenter the data.
Depending on the application, it may be more efficient to capture the raw data the first time it is entered and store in a file.
A program or many different programs can then read the file and process the data in different ways.
We should capture and validate the data at its points of origination (ie cash register, sales clerk).
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6. CS11 Assignment We have a file named catalogs.txt
The file has 7 catalog names as separate records.
To process the file:
open file.
read a catalog name and load it into the combo box.
need a loop to read and load each record.
allow users to add and remove catalog names.
and then save the results back to catalogs.txt.
Sequential file Processing – processing the records in the order they are stored in the file.
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7. catalogs.txt
Odds and Ends Solutions Camping Needs ToolTime Spiegel The Outlet
This is a simple text file.
The file can be created with Notepad or some other text editor.
Just enter values and press return at the of each record, including the last one.
The file should be saved in the Debug folder within the bin folder of the project folder.
CS11 > bin > Debug > catalogs.txt
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8. Sample Interface - same as CS10
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9. using System.IO;
The classes for data processing are defined in the System.IO namespace.
FileStream, StreamReader and StreamWriter
IO stands for Input/Output
These class definitions are NOT automatically included in C# projects.
Use the using command at the top of program before the form declaration to include the class definitions. using System.IO; namespace CS11 {         public partial class CS11Form : Form         {
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10. Form Load Event
The form load event is triggered when a form is first loaded.
In the method that captures this event, we can add code to initialize or load data that should be available when the form is displayed.
We will place the code to load the catalog names from the file into the items collection of the combo box in the form load event method.
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11. Load Data Procedure
private void CS11Form_Load(object sender, EventArgs e) {
string strCatalogName; try { FileStream catalogFileIn = new FileStream("Catalogs.txt", FileMode.Open); //Define file StreamReader catalogStreamReader = new StreamReader(catalogFileIn); //Open file
while (catalogStreamReader..Peek() != -1) //Test for EOF { strCatalogName = catalogStreamReader.ReadLine( ); //Read record
catalogComboBox.Items.Add(strCatalogName); //Add catalog name }
catalogStreamReader.Close( ); //Close file }
catch {
DialogResult responseDialogResult; responseDialogResult = MessageBox.Show("File does not exist. Do you wish to create it?", "File Not Found", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
if (responseDialogResult != DialogResult.Yes)
this.Close( ); //End the program
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12. Internal and External File Names
catalogs.txt is the external file name.
catalogFileIn is the internal file name.
FileStream catalogFileIn = new FileStream("Catalogs.txt", FileMode.Open); connects the internal name to the external file.
Naming conventions for the external file names vary by Operating Systems (OS).
Internal names conform to variable naming rules.
In new FileStream is the only place we see the external name.
The default folder is the same folder that executable is saved in (Debug folder inside of bin folder). A directory path can be included as part of the external filename.
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13. Use Try/Catch When Opening Files
try { FileStream catalogFileIn = new FileStream("Catalogs.txt", FileMode.Open); //Define file StreamReader catalogStreamReader = new StreamReader(catalogFileIn); //Open file
while (catalogStreamReader..Peek() != -1) //Test for EOF { strCatalogName = catalogStreamReader.ReadLine( ); //Read record
catalogComboBox.Items.Add(strCatalogName); //Add catalog name }
catalogStreamReader.Close( ); //Close file }
catch {
DialogResult responseDialogResult; responseDialogResult = MessageBox.Show("File does not exist. Do you wish to create it?", "File Not Found", MessageBoxButtons.YesNo, MessageBoxIcon.Question);
if (responseDialogResult != DialogResult.Yes)
this.Close( ); //End the program
Some possible errors:
File not found
Protection violation on network
Disk Full
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14. Process the file
When the input is from a file, it is referred to as the reading the file.
Saving to a file is referred to as Writing to the file.
In the loop we continue reading the file until we reach the End Of File (EOF).
EOF is set by the operating system (OS) when the last record is read.
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15. EOF Flag
Flag is a term used for variables that can have two possible values.
On or off, 0 or 1
Y or N, True or false
EOF – is it at the end of the file or not?
In this example the Peek method is used to check for EOF. while (catalogStreamReader.Peek( ) != -1)
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16. Close File catalogStreamReader.Close( );
Close releases file to Operating System (OS).
Other users may get file locked error if file is not closed.
Good housekeeping.
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17. blnIsDataSaved Flag
Need to track when data has been changed, but not yet saved.
If users Add, Remove, or Clear an item from the list, the blnIsDataSaved must be set to false.
In the FormClosing method, the flag is checked and if it is false the user is asked if they want to save the changes before exiting.
If the user says yes, then the File Save method is called.
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18. Form Closing Event
If user’s click on a Close button or Exit menu item, we can capture those events.
If the user clicks on the close window icon, an event is not fired.
However, when the form is instructed to close (this.Close), the Form Closing event is fired, and we can add a handler for that event.
Create a method and add the code to check if the data has been saved in the form closing method.
After writing this method to handle the FormClosing event, its needs to be assigned as the form's FormClosing event handler while in Design Mode.
After assigning it to the form, the method is automatically executed when the form is instructed to close.
In the Close button or Exit menu method, just call this.Close( ) and that will trigger the Form Closing event.
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19. Exit and Closing Procedure
private void mnuFileExit_Click( … ) { //blnIsDataSaved checked in Form Closing event procedure this.Close( ); } private void CS11Form_FormClosing( … ) { DialogResult dgrResponse; if (blnIsDataSaved = = false) { dgrResponse = MessageBox.Show("Do you wish to save the list?", "Save", MessageBoxButtons.YesNoCancel, MessageBoxIcon.Question); if (dgrResponse = = DialogResult.Yes) mnuFileSave_Click(mnuFileSave, new EventArgs( )); if (responseDialogResult == DialogResult.Cancel) e.Cancel = true; //cancel close event } }
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20. File Save Method
private void mnuFileSave_Click(object sender, EventArgs e ) {
int intIndex, intMaximum; try { FileStream catalogFileOut = new FileStream("Catalogs.txt", FileMode.Create); StreamWriter catalogStreamWriter = new StreamWriter(catalogFileOut); intMaximum = cboCatalog.Items.Count;
for (intIndex = 0; intIndex < intMaximum; intIndex++) {
catalogStreamWriter.WriteLine(cboCatalog.Items[intIndex]); }
catalogStreamWriter.Close( ); blnIsDataSaved = true: } catch { MessageBox.Show("Error saving the changes to the data file.", "Error Saving Data", MessageBoxButtons.OK, MessageBoxIcon.Error); } }
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21. Open for Output (.Create)
FileStream catalogFileOut = new FileStream("Catalogs.txt", FileMode.Create); StreamWriter catalogStreamWriter = new StreamWriter(catalogFileOut);
Create erases existing data, or creates a new file.
There is an Append option, which adds data to the end of an existing file. FileStream catalogFileOut = new FileStream("Catalogs.txt", FileMode.Append);
In CS11 we want to create an new file each time because the entire list is saved. If we append the data, we will end up with duplicate records.
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22. WriteLine Method Use WriteLine method to store data to a file.
catalogStreamWriter.WriteLine(cboCatalog.Items[intIndex]);
Use WriteLine method to store data to a file.
WriteLine adds a carriage return and linefeed at the end of each record.
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23. Close File catalogStreamWriter.Close( );
Close releases file to Operating System (OS).
Other users may get file locked error if file is not closed.
Good housekeeping.
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24. Posttests and Reading Files
Do loops (posttest) do NOT handle empty files. do { strCatalogName = catalogStreamReader.ReadLine( ); recordCount ++; } while (catalogStreamReader.Peek != -1); //recordCount would = one instead of zero for an empty file
Use while (pretest) for file processing. while (catalogStreamReader.Peek != -1) { strCatalogName = catalogStreamReader.ReadLine( ); recordCount ++; } //recordCount would = zero for an empty file
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25. ReadLine and EOF
Note that ReadLine does NOT throw an exception when you attempt to read past the end of the file.
That is why it is important to use a pretest loop, so that we can check if we are at the end of the file before attempting ReadLine.
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26. Summary Information Processing Cycle File Processing
Some code for CS11 was revealed .
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