Parsing extra characters from Datetime

Question

Hi I have following code that reads the date from a file.

using (var reader = new StreamReader(@"C:\myfile.txt")) 
{
    bool found= false;
    while (!reader.EndOfStream) 
  {
        var line = reader.ReadLine().Trim();

        if (found && line.EndsWith("Test")) 
        {
            var fordDate = DateTime.Parse(line.Substring(0, 19));
            Console.WriteLine("Test Date: {0}", fordDate);
            break;
        }
   }
 }

Problem is that it gives error when date has some other text connected with it. For example

\r\n2013-03-03 12:22:02 

I am trying to change it so that code can remove "\r\n" or any other text from it and just get the date part.

Answer 1

You should use regular expressions

If your dates are always of the same format, you can easily write a regular expression that will extract dates from individual lines and strip anything else on each side. For the purpose of understanding regular expression should look like this:

\d{4}-\d{2}-\d{2}\s\d{2}:\d{2}:\d{2}

This regular expression is too simplified and allows dates like 0000-00-00 99:99:99 which is likely invalid. It depends whether your file can hold some values that may apear as dates, but are not. A more complex (but more valid) expression would be (assuming that date is YYYY-MM-DD and not YYYY-DD-MM):

[12]\d{3}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])\s(?:[01]\d|2[0-3]):(?:[0-5]\d):(?:[0-5]\d)

This one will allow dates from year 1000 to 2999 with correct month numbers from 01-12 and days from 01-31 and hours from 00:00:00 to 23:59:59.

But to make this regular expression more useful I'll put it in parentheses and give it a name so these dates will become part of a named capture group (date) in your code that you can access using its name rather than index.

Regex rx = "(?<date>[12]\d{3}-(?:0\d|1[0-2])-(?:0[1-9]|[12]\d|3[01])\s(?:[01]\d|2[0-3]):(?:[0-5]\d):(?:[0-5]\d)).*Test$";
if (rx.Text(line))
{
    Match m = rx.Match(line);
    // no need to use TryParse as regex assures correct formatting
    fordDate = DateTime.Parse(m.Groups["date"]);
}

So instead of checking manually that line ends with Test I've also included the same requirement in the regular expression.

Answer 2

Use this code to replace symbols you need:

string lineAfterReplace = line.Replace("\t", "").Replace("\r", "").Replace("\n", "");

@J. Davidson - it may be also better for you to use TryParse MSDN Link

than you have some kind of this code:

if (DateTime.TryParse(dateString, out dateValue))
{
   /* it was parsed without errors */
}