C#

if (txtMyText.Text.Trim().Length != 0)
  ...

string val//your strings
MessageBox.Show(Regex.Match(val, @"HKEY_CLASSES_ROOT\\[^\\]*").ToString());

bool isMatch = Regex.IsMatch(keyPath);

Regex = {HKEY_CLASSES_ROOT\\[^\\]*}
keyPath = "hkey_classes_root\\.123\\openwithprogids"
isMatch = true

String input = @"HKEY_CLASSES_ROOT\.123\OpenWithProgIDs
           HKEY_CLASSES_ROOT\.ac3\OpenWithList\CTCMSu.exe";<br><br><br>
Regex r = new System.Text.RegularExpressions.Regex(@"HKEY_CLASSES_ROOT\\(?<subkey>[^\\]*)", 
      RegexOptions.Compiled | RegexOptions.IgnoreCase);


MatchCollection coll = r.Matches(input);


foreach (Match match in coll)
   {
   string subKey = match.Groups["subkey"].Value;
   Console.WriteLine("subkey = {0}" , subKey);
   }

System.Text.RegularExpressions.Match match = Regex.Match(keyPath);<br />
<br />
return (match.Groups[0].Success && match.Groups[0].Value == keyPath);<br />

public class Cache
{
  private List<IMemento> _cache = new List<IMemento>
  public void AddToCache<T>(T cacheItem)
  {
    _cache.Add(new MementoCache(cacheItem));
  }

  public T CancelChanges<T>(T cacheItem)
  {
    // Get the original item out of the cache and remove it.
    T item = _cache[...];
    _cache.Remove(...);
    return item;
  }

  internal class CacheMemento : IMemento
  {
    public void AddToCache<T>(T cacheItem)
    {
      // Save this item.
    }
  }
}