RegularExpressions in MQL4 for working with regular expressions - library for MetaTrader 4

Real author:

Microsoft Corporation. Source code taken from .Net Framework 4.6.1. 

Here is a translation of the RegularExpressions from .Net Framework 4.6.1.

To work with the library, include the Regex.mqh file from the "\MQL4\Include\RegularExpressions\" directory in your code.

Several illustrative examples are provided with the library, which at the same time serve as the test cases. All the samples are taken from the official site of Microsoft Corporation, they vividly demonstrate the main differences from the regular expressions in C# and the features of their use in the MQL4.

Below is more detailed information about RegularExpressions MQL4 ported library packages:

The regular expression parameters from the file RegexOptions.mqh:

Working with RegularExpressions for MQL4:

1. As withe the version for .Net, this library implements a storage (static cache) of regular expressions. All implicitly created regular expressions (instances of the Regex class) are written to that storage. This approach speeds up the operation of the scripts, as it eliminates the need to rebuild the regular expression if its pattern matches any of the existing ones. The default size of the storage is 15. The Regex::CacheSize() method returns or sets the maximum number of entries in the current static cache of the complied regular expressions.
   
2. The second feature of working with regular expression in MQL4 directly follows from the first one. And it lies in the fact that the above storage must be cleared. To do that, call the Regex::ClearCache() static function. It is recommended to call this function only after the work with the regular expressions has been completed, otherwise there is a risk to delete necessary pointers.
3. Unlike the .Net, the MQL4 does not implement the foreach loop, and hence the enumeration handling will be different. Example:

   //--- Code in C#
   Regex rx = new Regex(@"\b(?<word>\w+)\s+(\k<word>)\b", RegexOptions.IgnoreCase);   
   string text = "The the quick brown fox  fox jumped over the lazy dog dog.";
   MatchCollection matches = rx.Matches(text);
   foreach (Match match in matches) 
     {
      //--- handling
     }
   
   //--- Code in MQL4
   Regex *rx = new Regex("\\b(?<word>\\w+)\\s+(\\k<word>)\\b", RegexOptions::IgnoreCase);        
   string text = "The the quick brown fox  fox jumped over the lazy dog dog.";
   MatchCollection *matches = rx.Matches(text);
   IEnumerator<Match*> *en = matches.GetEnumerator();
   while(en.MoveNext()) 
     {
      Match *match = en.Current();
      //--- handling
     }
   delete rx;
   delete matches;
   delete en;
   Regex::ClearCache();
   

4. As can be seen from the above example, the C# syntax allows to put the '@' symbol in front of the strings to ignore all formatting marks in it. In MQL4, this approach is not provided, so all control characters in a regular expression pattern should be explicitly defined.

To learn more about the RegularExpressions for MQL4 and its features, use the provided Tests.mqh expert. It implements numerous examples of regular expression usage, which cover all the main functionality of the library.