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Regex.CompileToAssembly Method (RegexCompilationInfo[], AssemblyName, CustomAttributeBuilder[])

Compiles one or more specified Regex objects to a named assembly with the specified attributes.

Namespace:  System.Text.RegularExpressions
Assembly:  System (in System.dll)

[HostProtectionAttribute(SecurityAction.LinkDemand, MayLeakOnAbort = true)]
public static void CompileToAssembly(
	RegexCompilationInfo[] regexinfos,
	AssemblyName assemblyname,
	CustomAttributeBuilder[] attributes


Type: System.Text.RegularExpressions.RegexCompilationInfo[]
An array that describes the regular expressions to compile.
Type: System.Reflection.AssemblyName
The file name of the assembly.
Type: System.Reflection.Emit.CustomAttributeBuilder[]
An array that defines the attributes to apply to the assembly.


The value of the assemblyname parameter's AssemblyName.Name property is an empty or null string.


The regular expression pattern of one or more objects in regexinfos contains invalid syntax.


assemblyname or regexinfos is null.

The CompileToAssembly(RegexCompilationInfo[], AssemblyName, CustomAttributeBuilder[]) method generates a .NET Framework assembly in which each regular expression defined in the regexinfos array is represented by a class. Typically, the CompileToAssembly(RegexCompilationInfo[], AssemblyName, CustomAttributeBuilder[]) method is called from a separate application that generates an assembly of compiled regular expressions. Each regular expression included in the assembly has the following characteristics:

  • It is derived from the Regex class.

  • It is assigned the fully qualified name that is defined by the fullnamespace and name parameters of its corresponding RegexCompilationInfo object.

  • It has a default (or parameterless) constructor.

Ordinarily, the code that instantiates and uses the compiled regular expression is found in an assembly or application that is separate from the code that creates the assembly.

Because the CompileToAssembly method generates a .NET Framework assembly from a method call instead of using a particular language's class definition keyword (such as class in C# or ClassEnd Class in Visual Basic), it does not allow .NET Framework attributes to be assigned to the assembly by using the development language's standard attribute syntax. The attributes parameter provides an alternative method for defining the attributes that apply to the assembly. For each attribute that you want to apply to the assembly, do the following:

  1. Create an array of Type objects representing the parameter types of the attribute constructor that you want to call.

  2. Retrieve a Type object representing the attribute class that you want to apply to the new assembly.

  3. Call the GetConstructor method of the attribute Type object to retrieve a ConstructorInfo object representing the attribute constructor that you want to call. Pass the GetConstructor method the array of Type objects that represents the constructor's parameter types.

  4. Create a Object array that defines the parameters to pass to the attribute's constructor.

  5. Instantiate a CustomAttributeBuilder object by passing its constructor the ConstructorInfo object retrieved in step 3 and the Object array created in step 4.

You can then pass an array of these CustomAttributeBuilder objects instead of the attributes parameter to the Regex.CompileToAssembly(RegexCompilationInfo[], AssemblyName, CustomAttributeBuilder[]) method.


The HostProtectionAttribute attribute applied to this type or member has the following Resources property value: MayLeakOnAbort. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

The following example creates an assembly named RegexLib.dll and applies the AssemblyTitleAttribute attribute to it. The assembly includes two compiled regular expressions. The first, Utilities.RegularExpressions.DuplicatedString, matches two identical contiguous words. The second, Utilities.RegularExpressions.EmailAddress, checks whether a string has the correct format to be an e-mail address.

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;
using System.Text.RegularExpressions;

public class RegexCompilationTest
   public static void Main()
      RegexCompilationInfo expr;
      List<RegexCompilationInfo> compilationList = new List<RegexCompilationInfo>();

      // Define regular expression to detect duplicate words
      expr = new RegexCompilationInfo(@"\b(?<word>\w+)\s+(\k<word>)\b", 
                 RegexOptions.IgnoreCase | RegexOptions.CultureInvariant, 
      // Add info object to list of objects

      // Define regular expression to validate format of email address
      expr = new RegexCompilationInfo(@"^(?("")(""[^""]+?""@)|(([0-9A-Z]((\.(?!\.))|[-!#\$%&'\*\+/=\?\^`\{\}\|~\w])*)(?<=[0-9A-Z])@))" + 
                 RegexOptions.IgnoreCase | RegexOptions.CultureInvariant, 
      // Add info object to list of objects

      // Apply AssemblyTitle attribute to the new assembly
      // Define the parameter(s) of the AssemblyTitle attribute's constructor 
      Type[] parameters = { typeof(string) };
      // Define the assembly's title
      object[] paramValues = { "General-purpose library of compiled regular expressions" };
      // Get the ConstructorInfo object representing the attribute's constructor
      ConstructorInfo ctor = typeof(System.Reflection.AssemblyTitleAttribute).GetConstructor(parameters);
      // Create the CustomAttributeBuilder object array
      CustomAttributeBuilder[] attBuilder = { new CustomAttributeBuilder(ctor, paramValues) }; 

      // Generate assembly with compiled regular expressions
      RegexCompilationInfo[] compilationArray = new RegexCompilationInfo[compilationList.Count];
      AssemblyName assemName = new AssemblyName("RegexLib, Version=, Culture=neutral, PublicKeyToken=null");
      Regex.CompileToAssembly(compilationArray, assemName, attBuilder);                                                 

You can verify that the AssemblyTitleAttribute attribute has been applied to the assembly by examining its manifest with a reflection utility such as ILDasm.

The regular expression that checks a string for duplicate words is then instantiated and used by the following example.

using System;
using Utilities.RegularExpressions;

public class CompiledRegexUsage
   public static void Main()
      string text = "The the quick brown fox  fox jumped over the lazy dog dog.";
      DuplicatedString duplicateRegex = new DuplicatedString(); 
      if (duplicateRegex.Matches(text).Count > 0)
         Console.WriteLine("There are {0} duplicate words in \n   '{1}'", 
            duplicateRegex.Matches(text).Count, text);
         Console.WriteLine("There are no duplicate words in \n   '{0}'", 
// The example displays the following output to the console:
//    There are 3 duplicate words in
//       'The the quick brown fox  fox jumped over the lazy dog dog.'

Successful compilation of this second example requires a reference to RegexLib.dll (the assembly created by the first example) to be added to the project.

.NET Framework

Supported in: 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.