Is there a way to find the first string that matches a DateTime format string?

Question

Given a date time format string, is there a standard way to find the first matching substring that matches that format?

for example, given...

d-MMM-yy H:mm:ss

and some text...

"blah 1 2 3 7-Jul-13 6:15:00 4 5 6 blah"

I'd expect it to return

"7-Jul-13 6:15:00"

Now I can find this string by doing parsing, but I'm wondering if there is any library support for doing this?

Answer 1

This may not be the most efficient but it seemed like an interesting question so I thought I'd try this method.

It takes your DateTime format string and makes a Regex string pattern out of it by replacing any letters with . and whitespace with \\s. It then creates a Regex object out of that pattern and tries to find the first match in the input sentence.

That match, if it exists, is then passed into a DateTime.TryParseExact call. I'm sure improvements can be made but this might help give a general idea on a technique that doesn't require hardcoding a Regex or the format of the input sentence.

string inputSentence = "blah 1 2 3 7-Jul-13 6:15:00 4 5 6 blah";

string dtformat = "d-MMM-yy H:mm:ss";

//convert dtformat into regex pattern
StringBuilder sb = new StringBuilder();
foreach (char c in dtformat)
{
    if (Char.IsLetter(c))
    {
       if (char.ToUpperInvariant(c) == 'D' || char.ToUpperInvariant(c) == 'H' || char.ToUpperInvariant(c) == 'S')            
          sb.Append(".{1,2}");
       else
          sb.Append(".");
    }
    else if(Char.IsWhiteSpace(c))        
       sb.Append("\\s");
    else
       sb.Append(c);
}


string dtPattern = sb.ToString();

Regex dtrx = new Regex(dtPattern);

//get the match using the regex pattern
var dtMatch = dtrx.Match(inputSentence);

if(dtMatch != null)
{
    string firstString = dtMatch.Value.Trim();

    //try and parse the datetime from the string
    DateTime firstMatch;
    if (DateTime.TryParseExact(dstr, dtformat, null, DateTimeStyles.None, out firstMatch))
    {
       Console.WriteLine("Parsed");
    }
    else
    {
       Console.WriteLine("Could not parse");
    }
}