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

问题

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#.

回答1:

Use the correct constructor:

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

回答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

回答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!");
   }
}

回答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(); 

回答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");

回答6:

You just want to open the file in "append" mode.

http://msdn.microsoft.com/en-us/library/3zc0w663.aspx

回答7:

When you start StreamWriter it's override the text was there before. You can use append property like so:

TextWriter t = new StreamWriter(path, true);

回答8:

 else if (File.Exists(path)) 
{ 
  using (StreamWriter w = File.AppendText(path))
        {
            w.WriteLine("The next line!"); 
            w.Close();
        }
 } 

回答9:

You could use a FileStream. This does all the work for you.

http://www.csharp-examples.net/filestream-open-file/

回答10:

From microsoft documentation, you can create file if not exist and append to it in a single call File.AppendAllText Method (String, String)

.NET Framework (current version) Other Versions

Opens a file, appends the specified string to the file, and then closes the file. If the file does not exist, this method creates a file, writes the specified string to the file, then closes the file. Namespace: System.IO Assembly: mscorlib (in mscorlib.dll)

Syntax C#C++F#VB public static void AppendAllText( string path, string contents ) Parameters path Type: System.String The file to append the specified string to. contents Type: System.String The string to append to the file.

AppendAllText

回答11:

using(var tw = new StreamWriter(path, File.Exists(path)))
{
    tw.WriteLine(message);
}

回答12:

Try this.

string path = @"E:\AppServ\Example.txt";
if (!File.Exists(path))
{
    using (var txtFile = File.AppendText(path))
    {
        txtFile.WriteLine("The very first line!");
    }
}
else if (File.Exists(path))
{     
    using (var txtFile = File.AppendText(path))
    {
        txtFile.WriteLine("The next line!");
    }
}

回答13:

You can just use File.AppendAllText() Method this will solve your problem. This method will take care of File Creation if not available, opening and closing the file.

var outputPath = @"E:\Example.txt";
var data = "Example Data";
File.AppendAllText(outputPath, data);

来源：https://stackoverflow.com/questions/9907682/create-a-txt-file-if-doesnt-exist-and-if-it-does-append-a-new-line