Create a .txt file if doesn't exist, and if it does append a new line

c# text-files

I would like to create a .txt file and write to it, and if the file already exists I just want to append some more lines:

string path = @"E:\AppServ\Example.txt";
if (!File.Exists(path))
{
    File.Create(path);
    TextWriter tw = new StreamWriter(path);
    tw.WriteLine("The very first line!");
    tw.Close();
}
else if (File.Exists(path))
{
    TextWriter tw = new StreamWriter(path);
    tw.WriteLine("The next line!");
    tw.Close(); 
}

But the first line seems to always get overwritten... how can I avoid writing on the same line (I'm using this in a loop)?

I know it's a pretty simple thing, but I never used the WriteLine method before. I'm totally new to C#.

Solution 1:

Use the correct constructor:

else if (File.Exists(path))
{
    using(var tw = new StreamWriter(path, true))
    {
        tw.WriteLine("The next line!");
    }
}

Solution 2:

string path = @"E:\AppServ\Example.txt";
File.AppendAllLines(path, new [] { "The very first line!" });

See also File.AppendAllText(). AppendAllLines will add a newline to each line without having to put it there yourself.

Both methods will create the file if it doesn't exist so you don't have to.

File.AppendAllText
File.AppendAllLines

Solution 3:

string path=@"E:\AppServ\Example.txt";

if(!File.Exists(path))
{
   File.Create(path).Dispose();

   using( TextWriter tw = new StreamWriter(path))
   {
      tw.WriteLine("The very first line!");
   }

}    
else if (File.Exists(path))
{
   using(TextWriter tw = new StreamWriter(path))
   {
      tw.WriteLine("The next line!");
   }
}

Solution 4:

You don't actually have to check if the file exists, as StreamWriter will do that for you. If you open it in append-mode, the file will be created if it does not exists, then you will always append and never over write. So your initial check is redundant.

TextWriter tw = new StreamWriter(path, true);
tw.WriteLine("The next line!");
tw.Close();

Solution 5:

File.AppendAllText adds a string to a file. It also creates a text file if the file does not exist. If you don't need to read content, it's very efficient. The use case is logging.

File.AppendAllText("C:\\log.txt", "hello world\n");