C#: Prepending to beginning of a file

What is the best way to add text to the beginning of a file using C#?

I couldn't find a straightforward way to do this, but came up with a couple work-arounds.

1. Open up new file, write the text that I wanted to add, append the text from the old file to the end of the new file.

2. Since the text I want to add should be less than 200 characters, I was thinking that I could add white space characters to the beginning of the file, and then overwrite the white space with the text I wanted to add.

Has anyone else come across this problem, and if so, what did you do?

Solution 1:

This works for me, but for small files. Probably it's not a very good solution otherwise.

string currentContent = String.Empty;
if (File.Exists(filePath))
{
    currentContent = File.ReadAllText(filePath);
}
File.WriteAllText(filePath, newContent + currentContent );

Solution 2:

Adding to the beginning of a file (prepending as opposed to appending) is generally not a supported operation. Your #1 options is fine. If you can't write a temp file, you can pull the entire file into memory, preprend your data to the byte array and then overwrite it back out (this is only really feasible if your files are small and you don't have to have a bunch in memory at once because prepending the array is not necessarily easy without a copy either).

Solution 3:

Yeah, basically you can use something like this:

public static void PrependString(string value, FileStream file)
{
     var buffer = new byte[file.Length];

     while (file.Read(buffer, 0, buffer.Length) != 0)
     {
     }

     if(!file.CanWrite)
         throw new ArgumentException("The specified file cannot be written.", "file");

     file.Position = 0;
     var data = Encoding.Unicode.GetBytes(value);
     file.SetLength(buffer.Length + data.Length);
     file.Write(data, 0, data.Length);
     file.Write(buffer, 0, buffer.Length);
 }

 public static void Prepend(this FileStream file, string value)
 {
     PrependString(value, file);
 }

Then

using(var file = File.Open("yourtext.txt", FileMode.Open, FileAccess.ReadWrite))
{
    file.Prepend("Text you want to write.");
}

Not really effective though in case of huge files.