Regular Expression Example: Changing Date Formats

The following code example uses the System.Text.RegularExpressions.Regex.Replace method to replace dates that have the form mm/dd/yy with dates that have the form dd-mm-yy.

Example

sample · csharpsamples/snippets/csharp/VS_Snippets_CLR/RegularExpressions.Examples.ChangeDateFormats/cs/Example_ChangeDateFormats1.cs1

csharp

// <Snippet2>
using System;
using System.Globalization;
using System.Text.RegularExpressions;

public class Class1
{
   public static void Main()
   {
      string dateString = DateTime.Today.ToString("d",
                                        DateTimeFormatInfo.InvariantInfo);
      string resultString = MDYToDMY(dateString);
      Console.WriteLine($"Converted {dateString} to {resultString}.");
   }

   // <Snippet1>
   static string MDYToDMY(string input)
   {
      try {
         return Regex.Replace(input,
                @"\b(?<month>\d{1,2})/(?<day>\d{1,2})/(?<year>\d{2,4})\b",
               "${day}-${month}-${year}", RegexOptions.None,
               TimeSpan.FromMilliseconds(150));
      }
      catch (RegexMatchTimeoutException) {
         return input;
      }
   }
   // </Snippet1>
}
// The example displays the following output to the console if run on 8/21/2007:
//      Converted 08/21/2007 to 21-08-2007.
// </Snippet2>

sample · vbsamples/snippets/visualbasic/VS_Snippets_CLR/RegularExpressions.Examples.ChangeDateFormats/vb/Example_ChangeDateFormats1.vb1

' Visual Basic .NET Document
Option Strict On

' <Snippet2>
Imports System.Globalization
Imports System.Text.RegularExpressions

Module DateFormatReplacement
    Public Sub Main()
        Dim dateString As String = Date.Today.ToString("d", _
                                             DateTimeFormatInfo.InvariantInfo)
        Dim resultString As String = MDYToDMY(dateString)
        Console.WriteLine("Converted {0} to {1}.", dateString, resultString)
    End Sub

    ' <Snippet1>
    Function MDYToDMY(input As String) As String
        Try
            Return Regex.Replace(input, _
                   "\b(?<month>\d{1,2})/(?<day>\d{1,2})/(?<year>\d{2,4})\b", _
                   "${day}-${month}-${year}", RegexOptions.None,
                   TimeSpan.FromMilliseconds(150))
        Catch e As RegexMatchTimeoutException
            Return input
        End Try
    End Function
    ' </Snippet1>
End Module
' The example displays the following output to the console if run on 8/21/2007:
'      Converted 08/21/2007 to 21-08-2007.
' </Snippet2>

The following code shows how the MDYToDMY method can be called in an application.

sample · csharpsamples/snippets/csharp/VS_Snippets_CLR/RegularExpressions.Examples.ChangeDateFormats/cs/Example_ChangeDateFormats1.cs2

csharp

// <Snippet2>
using System;
using System.Globalization;
using System.Text.RegularExpressions;

public class Class1
{
   public static void Main()
   {
      string dateString = DateTime.Today.ToString("d",
                                        DateTimeFormatInfo.InvariantInfo);
      string resultString = MDYToDMY(dateString);
      Console.WriteLine($"Converted {dateString} to {resultString}.");
   }

   // <Snippet1>
   static string MDYToDMY(string input)
   {
      try {
         return Regex.Replace(input,
                @"\b(?<month>\d{1,2})/(?<day>\d{1,2})/(?<year>\d{2,4})\b",
               "${day}-${month}-${year}", RegexOptions.None,
               TimeSpan.FromMilliseconds(150));
      }
      catch (RegexMatchTimeoutException) {
         return input;
      }
   }
   // </Snippet1>
}
// The example displays the following output to the console if run on 8/21/2007:
//      Converted 08/21/2007 to 21-08-2007.
// </Snippet2>

sample · vbsamples/snippets/visualbasic/VS_Snippets_CLR/RegularExpressions.Examples.ChangeDateFormats/vb/Example_ChangeDateFormats1.vb2

' Visual Basic .NET Document
Option Strict On

' <Snippet2>
Imports System.Globalization
Imports System.Text.RegularExpressions

Module DateFormatReplacement
    Public Sub Main()
        Dim dateString As String = Date.Today.ToString("d", _
                                             DateTimeFormatInfo.InvariantInfo)
        Dim resultString As String = MDYToDMY(dateString)
        Console.WriteLine("Converted {0} to {1}.", dateString, resultString)
    End Sub

    ' <Snippet1>
    Function MDYToDMY(input As String) As String
        Try
            Return Regex.Replace(input, _
                   "\b(?<month>\d{1,2})/(?<day>\d{1,2})/(?<year>\d{2,4})\b", _
                   "${day}-${month}-${year}", RegexOptions.None,
                   TimeSpan.FromMilliseconds(150))
        Catch e As RegexMatchTimeoutException
            Return input
        End Try
    End Function
    ' </Snippet1>
End Module
' The example displays the following output to the console if run on 8/21/2007:
'      Converted 08/21/2007 to 21-08-2007.
' </Snippet2>

Comments

The regular expression pattern \b(?<month>\d{1,2})/(?<day>\d{1,2})/(?<year>\d{2,4})\b is interpreted as shown in the following table.

Pattern	Description
`\b`	Begin the match at a word boundary.
`(?<month>\d{1,2})`	Match one or two decimal digits. This is the `month` captured group.
`/`	Match the slash mark.
`(?<day>\d{1,2})`	Match one or two decimal digits. This is the `day` captured group.
`/`	Match the slash mark.
`(?<year>\d{2,4})`	Match from two to four decimal digits. This is the `year` captured group.
`\b`	End the match at a word boundary.

The pattern ${day}-${month}-${year} defines the replacement string as shown in the following table.

Pattern	Description
`$(day)`	Add the string captured by the `day` capturing group.
`-`	Add a hyphen.
`$(month)`	Add the string captured by the `month` capturing group.
`-`	Add a hyphen.
`$(year)`	Add the string captured by the `year` capturing group.

#Example

#Comments

#See also

Example

Comments

See also