Creating a fixed width file in C#

Question

What is the best way to create a fixed width file in C#. I have a bunch of fields with lengths to write out. Say 20,80.10,2 etc all left aligned. Is there an easy way to do this?

Answer 1

You can use string.Format to easily pad a value with spaces e.g.

string a = String.Format("|{0,5}|{1,5}|{2,5}", 1, 20, 300); string b = String.Format("|{0,-5}|{1,-5}|{2,-5}", 1, 20, 300);  // 'a' will be equal to "|    1|   20|  300|" // 'b' will be equal to "|1    |20   |300  |" 

Answer 2

This is a system I made for a configurable Fixed Width file writing module. It's configured with an XML file, the relevant part looking like this:

<WriteFixedWidth Table="orders" StartAt="1" Output="Return">   <Position Start="1" Length="17" Name="Unique Identifier"/>   <Position Start="18" Length="3" Name="Error Flag"/>   <Position Start="21" Length="16" Name="Account Number" Justification="right"/>   <Position Start="37" Length="8" Name="Member Number"/>   <Position Start="45" Length="4" Name="Product"/>   <Position Start="49" Length="3" Name="Paytype"/>   <Position Start="52" Length="9" Name="Transit Routing Number"/> </WriteFixedWidth> 

StartAt tells the program whether your positions are 0-based or 1-based. I made that configurable because I would be copying down offsets from specs and wanted to have the config resemble the spec as much as possible, regardless of what starting index the author chose.

The Name attribute on the Position tags refer to the names of columns in a DataTable.

The following code was written for .Net 3.5, using LINQ-to-XML, so the method assumed it'd be passed an XElement with the above configuration, which you can get after you use XDocument.Load(filename) to load the XML file, then call .Descendants("WriteFixedWidth") on the XDocument object to get the configuration element.

    public void WriteFixedWidth(System.Xml.Linq.XElement CommandNode, DataTable Table, Stream outputStream)     {         StreamWriter Output = new StreamWriter(outputStream);         int StartAt = CommandNode.Attribute("StartAt") != null ? int.Parse(CommandNode.Attribute("StartAt").Value) : 0;          var positions = from c in CommandNode.Descendants(Namespaces.Integration + "Position")                         orderby int.Parse(c.Attribute("Start").Value) ascending                         select new                         {                             Name = c.Attribute("Name").Value,                             Start = int.Parse(c.Attribute("Start").Value) - StartAt,                             Length = int.Parse(c.Attribute("Length").Value),                             Justification = c.Attribute("Justification") != null ? c.Attribute("Justification").Value.ToLower() : "left"                         };          int lineLength = positions.Last().Start + positions.Last().Length;         foreach (DataRow row in Table.Rows)         {             StringBuilder line = new StringBuilder(lineLength);             foreach (var p in positions)                 line.Insert(p.Start,                      p.Justification == "left" ? (row.Field<string>(p.Name) ?? "").PadRight(p.Length,' ')                                               : (row.Field<string>(p.Name) ?? "").PadLeft(p.Length,' ')                      );             Output.WriteLine(line.ToString());         }         Output.Flush();     } 

The engine is StringBuilder, which is faster than concatenating immutable strings together, especially if you're processing multi-megabyte files.