DllImportAttribute Class

Definition

Namespace:

System.Runtime.InteropServices

Assembly:

System.Runtime.InteropServices.dll

Source:

DllImportAttribute.cs

Indicates that the attributed method is exposed by an unmanaged dynamic-link library (DLL) as a static entry point.

public ref class DllImportAttribute sealed : Attribute

[System.AttributeUsage(System.AttributeTargets.Method, Inherited=false)]
public sealed class DllImportAttribute : Attribute

[<System.AttributeUsage(System.AttributeTargets.Method, Inherited=false)>]
type DllImportAttribute = class
    inherit Attribute

Public NotInheritable Class DllImportAttribute
Inherits Attribute

Inheritance

Object

Attribute

DllImportAttribute

Attributes

AttributeUsageAttribute

Examples

The following code example shows how to use the DllImportAttribute attribute to import the Win32 MessageBox function. The code example then calls the imported method.

using System;
using System.Runtime.InteropServices;

class Example
{
    // Use DllImport to import the Win32 MessageBox function.
    [DllImport("user32.dll", CharSet = CharSet.Unicode)]
    public static extern int MessageBox(IntPtr hWnd, String text, String caption, uint type);
    
    static void Main()
    {
        // Call the MessageBox function using platform invoke.
        MessageBox(new IntPtr(0), "Hello World!", "Hello Dialog", 0);
    }
}

Imports System.Runtime.InteropServices

Module Example

    ' Use DllImport to import the Win32 MessageBox function.
    <DllImport("user32.dll", CharSet:=CharSet.Unicode)> _
    Function MessageBox(ByVal hwnd As IntPtr, ByVal t As String, ByVal caption As String, ByVal t2 As UInt32) As Integer
    End Function


    Sub Main()
        ' Call the MessageBox function using platform invoke.
        MessageBox(New IntPtr(0), "Hello World!", "Hello Dialog", 0)
    End Sub

End Module

Remarks

You can apply this attribute to methods.

The DllImportAttribute attribute provides the information needed to call a function exported from an unmanaged DLL. As a minimum requirement, you must supply the name of the DLL containing the entry point.

You apply this attribute directly to C# and C++ method definitions; however, the Visual Basic compiler emits this attribute when you use the Declare statement. For complex method definitions that include BestFitMapping, CallingConvention, ExactSpelling, PreserveSig, SetLastError, or ThrowOnUnmappableChar fields, you apply this attribute directly to Visual Basic method definitions.

Note JScript does not support this attribute. You can use C# or Visual Basic wrapper classes to access unmanaged API methods from JScript programs.

For additional information about using the platform invoke service to access functions in unmanaged DLLs, see Consuming Unmanaged DLL Functions.

Note

The DllImportAttribute does not support marshaling of generic types.

Constructors

DllImportAttribute(String)

Initializes a new instance of the DllImportAttribute class with the name of the DLL containing the method to import.

Fields

BestFitMapping	Enables or disables best-fit mapping behavior when converting Unicode characters to ANSI characters.
CallingConvention	Indicates the calling convention of an entry point.
CharSet	Indicates how to marshal string parameters to the method and controls name mangling.
EntryPoint	Indicates the name or ordinal of the DLL entry point to be called.
ExactSpelling	Controls whether the CharSet field causes the common language runtime to search an unmanaged DLL for entry-point names other than the one specified.
PreserveSig	Indicates whether unmanaged methods that have HRESULT return values are directly translated or whether HRESULT return values are automatically converted to exceptions.
SetLastError	Indicates whether the callee sets an error (SetLastError on Windows or errno on other platforms) before returning from the attributed method.
ThrowOnUnmappableChar	Enables or disables the throwing of an exception on an unmappable Unicode character that is converted to an ANSI "?" character.

Properties

TypeId	When implemented in a derived class, gets a unique identifier for this Attribute. (Inherited from Attribute)
Value	Gets the name of the DLL file that contains the entry point.

Methods

Equals(Object)	Returns a value that indicates whether this instance is equal to a specified object. (Inherited from Attribute)
GetHashCode()	Returns the hash code for this instance. (Inherited from Attribute)
GetType()	Gets the Type of the current instance. (Inherited from Object)
IsDefaultAttribute()	When overridden in a derived class, indicates whether the value of this instance is the default value for the derived class. (Inherited from Attribute)
Match(Object)	When overridden in a derived class, returns a value that indicates whether this instance equals a specified object. (Inherited from Attribute)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Returns a string that represents the current object. (Inherited from Object)

See also

• SetLastError
• ExactSpelling
• PreserveSig
• CallingConvention