'System.ArgumentOutOfRangeException' occurred in mscorlib.dll

Question

I'm writing an application to read the first line of a txt file and write to Excel.

The input line is like this, which has 94 characters in total, the last 8 can be blanks or 0's (the x's are actually blanks): 101x071000301x6759601771308202341F094101ACHxxxxxxxxxxxxxxxxxxxxFISxACHxMILWAUKEE‌​xxxxxxxx

When it prints, it correctly displays the x's as blank. Not sure about the last 8 blanks though.

The Console.WriteLine correctly outputs the string (which has blank spaces between characters), but when I try to extract the characters from the string I get this error:

'System.ArgumentOutOfRangeException' occurred in mscorlib.dll
Additional information: Index and length must refer to a location within the string.

while ((input = stream.ReadLine()) != null)
{
  //ACH HEADER LINE
  if (iCurRecLine == 0 && input.IndexOf(HeaderBeginKeyWord) >= 0)     
  {
    Console.WriteLine(input);

    RepDate = input.Substring(23, 6).Trim();
    RecordTypeCode = input.Substring(0, 1).Trim();
    PriorityCode = input.Substring(1, 2).Trim();
    ImmDestination = input.Substring(3, 10).Trim();
    ImmOrigin = input.Substring(13, 10).Trim();
    FileCreatedDate = input.Substring(23, 6).Trim();
    FileCreatedTime = input.Substring(29, 4).Trim();
    FileIDModifier = input.Substring(33, 1).Trim();
    RecordSize = input.Substring(34, 3).Trim();
    BlockingFactor = input.Substring(37, 2).Trim();
    FormatCode = input.Substring(39, 1).Trim();
    Destination = input.Substring(40, 23).Trim();
    Origin = input.Substring(63, 23).Trim();
    ReferenceCode = input.Substring(86, 8).Trim();
    ...
  }
}

Where did I go wrong on this?

Answer 1

There seems to be no validation in the file content you're reading.

.SubString() throws the ArgumentOutOfRangeException if the "startIndex plus length indicates a position not within this instance."

Therefore:

 RepDate = input.Substring(23, 6).Trim();

Could easily fail and throw this exception if the input only contains 10 characters.