C# string array buffer

Question

I am building an application for my brother that takes string input form an external source, GPS plotter, which I would like to display in a multiline textbox. If someone were to leave this application running for an extended period I don't want the TextBox.MaxLength to be exceeded or memory allocation to become excessive.

I can't think of a good way to implement this. I need to display the last n rows in a textbox.

Edit: The marked solution is correct. Thanks Jon. I ended up making it generic. Below is what I used.

public class ArrayBuffer<T>
{
    private readonly int _maxLines;
    private int _writePosition;

    private readonly T[] _buffer;

    public ArrayBuffer(int maxLines = 100)
    {
        _maxLines = maxLines;
        _buffer = new T[_maxLines];
    }

    public T[] Push(T value)
    {
        _buffer[_writePosition++] = value;
        _writePosition %= _maxLines;
        return _buffer.Skip(_writePosition)
                             .Concat(_buffer.Take(_writePosition))
                             .Where(line => line != null).ToArray();
    }
}

Usage:

var myArrayBuffer = new ArrayBuffer<string>(50);
string[] bufferedStringArray = myArrayBuffer.Push("some string");

Maybe sober up first?

Henk Holterman
– Henk Holterman

2013-07-06 20:58:27 +00:00
Commented Jul 6, 2013 at 20:58 — Henk Holterman
– Henk Holterman, Commented Jul 6, 2013 at 20:58
Haha. Riding the Ballmer Peak

TheGwa
– TheGwa

2013-07-06 21:06:15 +00:00
Commented Jul 6, 2013 at 21:06 — TheGwa
– TheGwa, Commented Jul 6, 2013 at 21:06

Jon · Accepted Answer · 2013-07-06 20:15:10Z

4

Assuming that an acceptable solution would be to display no more than the last N lines of output each time, you could keep a circular buffer of the last N lines of input. Whenever input arrives, the oldest lines in the buffer get deleted to make room for the new arrivals.

The parts that implement the buffer:

const int MAX_LINES = 10;
int writePosition = 0;
readonly string[] buffer = new string[MAX_LINES];

When new input arrives:

// input is an IEnumerable<string>
foreach (var line in input)
{
    buffer[writePosition++] = line;
    writePosition %= MAX_LINES;
}

When you want to display output:

var linesInDisplayOrder =  buffer.Skip(writePosition)
                                 .Concat(buffer.Take(writePosition))
                                 .Where(line => line != null);
var outputText = String.Join("\n", linesInDisplayOrder);

edited Jul 6, 2013 at 20:15

answered Jul 6, 2013 at 20:04

Jon

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1 Comment

TheGwa Over a year ago

A tip of the hat to you good sir. That is a surpassingly cunning solution.

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