C# Processing Fixed Width Files

Question

I have a collection of fixed width files with a varying number of columns and field sizes.

The top of the file starts with a line like:

AAAAABBCCCCCCCCCCDDD and so on

The change in character denotes the end of one field and the start of another. I am guessing this can someone be used to work out what the field sizes are with code and then apply the same values to the actual data lines below.

I then want to output all the read data into a XLS file or even a DataGrid, but my issue is I have no idea how to code this.

Any help would be greatly appreciated :)

---

/Edit:

I implemented Cuong's solution and although that worked fine for testing on my home PC, I had to compile it with c# v4 as our work PCs have Windows XP.

Anyways, when reading the input file I get the following error:

************** Exception Text **************
System.ObjectDisposedException: Cannot read from a closed TextReader.
   at System.IO.__Error.ReaderClosed()
   at System.IO.StreamReader.ReadLine()
   at System.IO.File.<InternalReadLines>d__0.MoveNext()
   at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
   at System.IO.File.InternalWriteAllLines(TextWriter writer, IEnumerable`1 contents)
   at System.IO.File.WriteAllLines(String path, IEnumerable`1 contents)
   at FixedWidthFiles.Main.buttonProcessFile_Click(Object sender, EventArgs e)
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Button.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)


************** Loaded Assemblies **************
mscorlib
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.1 (RTMRel.030319-0100)
    CodeBase: file:///C:/WINDOWS/Microsoft.NET/Framework/v4.0.30319/mscorlib.dll
----------------------------------------
FixedWidthFiles
    Assembly Version: 1.0.0.0
    Win32 Version: 1.0.0.0
    CodeBase: file:///C:/TEMP/FixedWidthFiles.exe
----------------------------------------
System.Windows.Forms
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.1 built by: RTMRel
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Windows.Forms/v4.0_4.0.0.0__b77a5c561934e089/System.Windows.Forms.dll
----------------------------------------
System.Drawing
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.1 built by: RTMRel
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Drawing/v4.0_4.0.0.0__b03f5f7f11d50a3a/System.Drawing.dll
----------------------------------------
System
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.1 built by: RTMRel
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System/v4.0_4.0.0.0__b77a5c561934e089/System.dll
----------------------------------------
System.Core
    Assembly Version: 4.0.0.0
    Win32 Version: 4.0.30319.1 built by: RTMRel
    CodeBase: file:///C:/WINDOWS/Microsoft.Net/assembly/GAC_MSIL/System.Core/v4.0_4.0.0.0__b77a5c561934e089/System.Core.dll
----------------------------------------

Answer 1

Below example how to write in csv file (excel type), the main point is you need to read the first line and calculate width:

var lines = File.ReadLines("C:\\input.txt");

var widthList = lines.First().GroupBy(c => c)
                             .Select(g => g.Count())
                             .ToList();

var list = new List<KeyValuePair<int, int>>();

int startIndex = 0;

for (int i = 0; i < widthList.Count(); i++)
{
    var pair = new KeyValuePair<int, int>(startIndex, widthList[i]);
    list.Add(pair);

    startIndex += widthList[i];
}

var csvLines = lines.Select(line => string.Join(",", 
                    list.Select(pair => line.Substring(pair.Key, pair.Value))));

File.WriteAllLines("C:\\test.csv", csvLines);