var lengths = new[] { 4, 6, 4, 7, 9 };
var parts = new string[lengths.Length];
// if you're not using .NET4 or above then use ReadAllLines rather than ReadLines
foreach (string line in File.ReadLines("YourFile.txt"))
{ int startPos = 0; for (int i = 0; i < lengths.Length; i++) { parts[i] = line.Substring(startPos, lengths[i]); startPos += lengths[i]; } // do something with "parts" before moving on to the next line
}