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Index › Programming Questions & Help › Syntax Questions › Append to a text file
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Append to a text file (Read 1280 times)
Giles
Append to a text file
Mar 4th, 2010, 9:40pm  
Is there any way to append to the end of a text file using PrintWriter? The only way I can think of (without going into Java methods) is to load the textfile into an array (loadStrings) and then write it back into the file and then write the new element at the end. Not very elegant....

Code:

PrintWriter output;


void setup()
{
  String lines[] = loadStrings("test.txt");
  output=createWriter("test.txt");
  for(int i=0; i<lines.length ; i++)
  {
    output.println(lines[i]);
  }
  output.println("Testing...testing...");
  output.flush();
  output.close();
}

void draw() {}


Running this repeatedly does add another line to the end of the text file every time....
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Cedric
Re: Append to a text file
Reply #1 - Mar 4th, 2010, 10:08pm  
http://processing.org/discourse/yabb2/num_1251025598.html
that will help
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Giles
Re: Append to a text file
Reply #2 - Mar 5th, 2010, 8:06am  
Thanks...I might use that method. I'm wondering if it really is less expensive though - "append" probably has to load the text file into memory anyway to append to it?

I guess it is the writing part that is  more expensive...
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PhiLho 
Re: Append to a text file
Reply #3 - Mar 5th, 2010, 8:40am  
Quote:
"append" probably has to load the text file into memory anyway to append to it?

No. The system probably offers an append mode to file writing, just adding data after data existing on disk. That append option leverages this capability, thus is much more efficient, particularly on large files.

Note: you can use yet another method, falling back on good old PrintWriter, which has the advantage to offer println (no worries about line ending) and printf (formatting), among other things:
Code:
PrintWriter pw = null;
try 
{
  pw = new PrintWriter(new BufferedWriter(new FileWriter(outFileName, true))); // true means: "append"
  pw.println(newData);
} 
catch (IOException e) 
{
  // Report problem or handle it
}
finally
{
  if (pw != null)
  {
    pw.close();
  }
}
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Giles
Re: Append to a text file
Reply #4 - Mar 5th, 2010, 1:49pm  
Very useful, thanks.
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