First, let’s see three different ways of extracting data from a file.

string fileText = File.ReadAllText(file);
string[] fileLines = File.ReadAllLines(file);
byte[] fileBytes = File.ReadAllBytes(file);

• On the first line, we read all the data in the file as a string.
• On the second line, we read the data in the file into a string-array. Each line in the file becomes an element in the array.
• On the third we read the bytes from the file.

Next, let’s see three different methods of appending data to a file. If the file you specify doesn’t exist, each method will automatically create the file before attempting to append the data to it.

File.AppendAllText(file, "Here is some data that is\\nappended to the file.");
File.AppendAllLines(file, new string[2] { "Here is some data that is", "appended to the file." });
using (StreamWriter stream = File.AppendText(file))
{
    stream.WriteLine("Here is some data that is");
    stream.Write("appended to the file.");
}

• On the first line we simply add a string to the end of the specified file.
• On the second line we add each element of the array onto a new line in the file.
• Finally on the third line we use File.AppendText to open up a streamwriter which will append whatever data is written to it.

And lastly, let’s see three different methods of writing data to a file. The difference between appending and writing being that writing over-writes the data in the file while appending adds to the data in the file. If the file you specify doesn’t exist, each method will automatically create the file before attempting to write the data to it.

File.WriteAllText(file, "here is some data\\nin this file.");
File.WriteAllLines(file, new string[2] { "here is some data", "in this file" });
File.WriteAllBytes(file, new byte[2] { 0, 255 });

• The first line writes a string to the file.
• The second line writes each string in the array on it’s own line in the file.
• And the third line allows you to write a byte array to the file.