The Basics

When you write program you will often find yourself in need to save data in some form. It might just be a username or a setting, but it might also be names and addresses or other data.
You might not always need an entire SQL database so you want to put it into a textfile(.txt).

C# makes it quite easy to work with input/output and it utilizes a Stream class.

Getting into it

The first thing you have to do is add the correct library at the top:

using System.IO;

This contains all classes we will need to read and write data to file.

Now, the code to write and read a file can be simple, like this:

using System;

using System.IO;



namespace IO

{

	class Program

	{

		public static void Main(string[] args)

		{

			//Specify a filestream containing the filename

			FileStream fs = new FileStream("path.txt", FileMode.OpenOrCreate, FileAccess.Write);

			

			//Create a stream to write to

			StreamWriter sw = new StreamWriter(fs);

			

			//Write

			sw.WriteLine("Hello world!");

			sw.WriteLine("What's hanging?");

			

			//Close the stream

			sw.Close();

			

			//Close the file

			fs.Close();

			

			//Specify the the file to read from

			fs = new FileStream("path.txt", FileMode.OpenOrCreate, FileAccess.Read);

			

			//Create a stream to read to

			StreamReader sr = new StreamReader(fs);

			

			//Read the file

			string theText = sr.ReadToEnd();

			

			Console.WriteLine(theText);

			

			sr.Close();

			

			fs.Close();

			

			Console.Read();

		}

	}

}

Advanced

Filestream:

FileStream fs = new FileStream("path.txt", FileMode.OpenOrCreate, FileAccess.Write);

This either creates a file if it doesn't exist or opens it if it already exists. It uses the FileMode, FileAccess enumeration.
These are the FileMode enumerations:

FileMode Enumeration	Description
Create	FileMode.Create value creates a file and if the file already exists, it will be overwritten.
CreateNew	Creates a file and if the file already exists, an IOException is thrown.
Append	Opens the file and starts writing at the end of the file. If the file doesn't exist a file is created. Note that you can use FileMode.Append only with FileAccess.Write or an exception of type ArgumentException is thrown.
Open	Opens the file if it exists. If the file does not exist, an exception of type FileNotFoundException is thrown.
OpenOrCreate	Opens the file if it exists. If the file does not exist, the file will be created.
Truncate	Opens a file and truncates it to make it a size of zero bytes.

These are the FileAccess enumerations:

FileAccess Enumeration	Description
Read	Sets read access to the file.
Write	Sets write access to the file.
ReadWrite	Sets read/write access to the file.

Then there is a third enumerator, FileShare, that provides values for how the file is shared with other streams by the running process or other processes.

FileShare Enumeration	Description
None	Obtains an exclusive access to the file until it's closed, which means that other streams can't read from or write to the file until this stream is closed.
Read	Other streams (in the current process or in another one) can obtain read access to the file.
Write	Other streams (in the current process or in another one) can obtain write access to the file
ReadWrite	Other streams can obtain ReadWrite access to the file

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