This documentation is archived and is not being maintained.

UnmanagedMarshal Class

Note: This API is now obsolete.

Represents the class that describes how to marshal a field from managed to unmanaged code. This class cannot be inherited.


Namespace:  System.Reflection.Emit
Assembly:  mscorlib (in mscorlib.dll)

[ObsoleteAttribute("An alternate API is available: Emit the MarshalAs custom attribute instead.")]
[HostProtectionAttribute(SecurityAction.LinkDemand, MayLeakOnAbort = true)]
public sealed class UnmanagedMarshal

The UnmanagedMarshal type exposes the following members.

Public propertyBaseTypeGets an unmanaged base type. This property is read-only.
Public propertyElementCountGets a number element. This property is read-only.
Public propertyGetUnmanagedTypeIndicates an unmanaged type. This property is read-only.
Public propertyIIDGuidGets a GUID. This property is read-only.

Public methodStatic memberDefineByValArraySpecifies a fixed-length array (ByValArray) to marshal to unmanaged code.
Public methodStatic memberDefineByValTStrSpecifies a string in a fixed array buffer (ByValTStr) to marshal to unmanaged code.
Public methodStatic memberDefineLPArraySpecifies an LPArray to marshal to unmanaged code. The length of an LPArray is determined at runtime by the size of the actual marshaled array.
Public methodStatic memberDefineSafeArraySpecifies a SafeArray to marshal to unmanaged code.
Public methodStatic memberDefineUnmanagedMarshalSpecifies a given type that is to be marshaled to unmanaged code.
Public methodEquals(Object)Determines whether the specified Object is equal to the current Object. (Inherited from Object.)
Protected methodFinalizeAllows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection. (Inherited from Object.)
Public methodGetHashCodeServes as a hash function for a particular type. (Inherited from Object.)
Public methodGetTypeGets the Type of the current instance. (Inherited from Object.)
Protected methodMemberwiseCloneCreates a shallow copy of the current Object. (Inherited from Object.)
Public methodToStringReturns a string that represents the current object. (Inherited from Object.)

The code example shows the workaround for this obsolete type.

Marshaling is the process of packaging and unpackaging parameters so remote procedure calls can occur. During marshaling, a field might undergo a format conversion when the format of the managed type is different from the format of the corresponding unmanaged type. For example, you might want to marshal a String type as an unmanaged BSTR. Some format conversions are handled automatically by the runtime. To override the default behavior, you must use the UnmanagedMarshal class to define the format conversion.


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 code example shows replacement code for the obsolete UnmanagedMarshal type. The example emits a single-module assembly named EmitMarshalAs.dll, containing a type named Sample. The type has a method named Test, with one parameter of type String. The code example applies the MarshalAsAttribute with UnmanagedType.BStr to the parameter.

You can use the Ildasm.exe (MSIL Disassembler) to examine the emitted assembly and observe that the parameter is marked marshal(bstr).

using System;
using System.Reflection;
using System.Reflection.Emit;
using System.Runtime.InteropServices;

public class Example
    public static void Main()
        AppDomain myDomain = AppDomain.CurrentDomain;
        AssemblyName myAsmName = new AssemblyName("EmitMarshalAs");

        AssemblyBuilder myAssembly = 

        ModuleBuilder myModule = 
               myAsmName.Name + ".dll");

        TypeBuilder myType = 
            myModule.DefineType("Sample", TypeAttributes.Public);

        MethodBuilder myMethod = 
            myType.DefineMethod("Test", MethodAttributes.Public,
                null, new Type[] { typeof(string) });

        // Get a parameter builder for the parameter that needs the 
        // attribute, using the HasFieldMarshal attribute. In this
        // example, the parameter is at position 0 and has the name
        // "arg".
        ParameterBuilder pb = 
               ParameterAttributes.HasFieldMarshal, "arg");

        // Get the MarshalAsAttribute constructor that takes an
        // argument of type UnmanagedType.
        ConstructorInfo ci = 
                new Type[] { typeof(UnmanagedType) });

        // Create a CustomAttributeBuilder representing the attribute,
        // specifying the necessary unmanaged type. In this case, 
        // UnmanagedType.BStr is specified.
        CustomAttributeBuilder cabuilder = 
            new CustomAttributeBuilder(
                ci, new object[] { UnmanagedType.BStr });

        // Apply the attribute to the parameter.

        // Emit a dummy method body.
        ILGenerator il = myMethod.GetILGenerator();

        Type finished = myType.CreateType();
        myAssembly.Save(myAsmName.Name + ".dll");

.NET Framework

Supported in: 1.1, 1.0
Obsolete (compiler warning) in 4
Obsolete (compiler warning) in 3.5
Obsolete (compiler warning) in 3.5 SP1
Obsolete (compiler warning) in 3.0
Obsolete (compiler warning) in 3.0 SP1
Obsolete (compiler warning) in 3.0 SP2
Obsolete (compiler warning) in 2.0
Obsolete (compiler warning) in 2.0 SP1
Obsolete (compiler warning) in 2.0 SP2

.NET Framework Client Profile

Obsolete (compiler warning) in 4
Obsolete (compiler warning) in 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.

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.