Writing Files

Introduction

The FileStream instance implements the IDisposable interface, so we must release the unmanaged resources after we’re done using the instance. In this lesson, we’ll look at how to write data to a file and read it back.

Encode and decode

If we want to write something to a file, we must convert it to an array of bytes. The specific means of converting a data type to a byte[] object varies depending on the nature of what we’ll store. Each file type has a specific format. For instance, we can encode text (string objects) using UTF8 encoding, ASCII, and so on. Depending on the encoding type, the array of bytes and the contents of the file are both different.

If we want to write some text to a file, we can use the Encoding class. It converts a .NET data type into an array of bytes:

string text = "Hello World!";
byte[] bytes = Encoding.UTF8.GetBytes(text);

Note: The Encoding class only works with text formats and text objects.

Write text

After we have a text encoded into a byte array, we can start writing it to a file stream (FileStream object). As when we read from a file, we first create an instance of the FileStream class:

using (var fileStream = new FileStream(fileName, FileMode.Create))
{
}

The FileMode.Create ensures that we create a new file. If the file already exists, then it is overwritten.

Next, we use the Write() method of the FileStream object to write our byte array to the file:

fileStream.Write(bytes, 0, bytes.Length);

The bytes, in our case, is the byte[] object we want to write, 0 is the offset (from which position we should start writing), and bytes.Length is the number of bytes we write. In this case, we write the whole byte array.

We can reverse the process to ensure that our text was written successfully: