FontysICT-sem1

Text File Handling

In order to write to a Text File or read from a Text File you must add the following at the top of the C# File:

using System.IO;

Sample code for reading from a TextFile

To read a Text File you need a so-called Stream needed on the File.

The path where the File is stored is relative to the executable, so search (by default) in your bin debug. With ‘…’ you go one directory higher: ‘../bloemkool.txt’.

Create a StreamReader on the stream:

StreamReader reader = new StreamReader(fileStream);

and then one line can be read in with

line = reader.ReadLine();

After the last line, ReadLine() returns a null. So by making a loop it is possible to read to the end. Finally, the reader and the stream must be Closed. Around them we put a try...catch...finally. If when executing the code in the try block an Exception occurs (could be that the File does not exist, or there are no read permissions) the program execution jumps immediately jumps to the catch-block: here you can see what is wrong. A message can be given to the user what is wrong, or something is stored in a log. Finally, the finally block: this is ALWAYS executed: both when there is an Exception and when the try block is has been executed successfully. By putting the Close in the finally block you can be sure that after the file is closed. So that looks like this:

String line;
try
{
	StreamReader reader = new StreamReader("C:³");
	// read the first line
	line = reader.ReadLine();

	//until you get to the end: read line by line.
	while (line != null)
	{
		// 'Process' you have to program yourself:
		Process(line);
		// read next line:
		line = reader.ReadLine();
	}
}
catch(Exception exc)
{
	// Handle the problem.
	HandleException(exc);
}
finally
{
	// and close the reader.
	reader.Close();
}

Writing a Text File

Writing is similar to reading:

try
{
	StreamWriter writer = new StreamWriter("C:``sprouts.txt'');
	// Write what you want to the File:
	// WriteLine for a line with so-called EndOfLine (EOL) after it.
	writer.WriteLine("Hello File.");
	// Write to write without EOL.
	writer.Write("Still ");
	writer.WriteLine("more text.");
}
catch(Exception exc)
{
	// Handle the problem.
	HandleException(exc);
}
finally
{
	writer.Close();
}

Creating a StreamWriter can also be done with other parameters, for example:

new StreamWriter("C:ids.txt", true, Encoding.ASCII);

• The encoding indicates how the characters in the File are encoded.
• In the example above, the true indicates whether to append or overwrite the File.

Terminology

You can figure this out further if you need to:

• What is the meaning of the following words?
  • File, File
  • Directory, Path, Folder, Folder
  • UNC
  • URL
• What does a path look like in Windows Explorer, Command Prompt, Linux, Mac OSX?

File handling classes

The .NET framework provides a number of classes* to handle files:

• File
• Directory
• DirectoryInfo
• Path

Something about Exception Handling.

FileNotFoundException, NullPointerException, and so on. All those errors that you see when you test a program the user also sees. But when the user sees them, his program crashes! As a software engineer, you need to avoid possible exceptional situations. C# has the keywords try, catch and finally for this. Regularly, you do not want to completely change the structure of your code to accommodate exceptional situations that you want to consider an exception. An example is when your program needs a connection to a database or sends requests to the Internet: you dont want to check every time if the connection to database or internet still works, but **if** the connection is lost then your program must be able to deal with that. In C# you do that by putting a try-catch-clause` around your code, as seen above.

Other resources on Exception Handling in C#

Exceptions at CSharp-station
Exceptions at MSDN
MSDN

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