Marshal.QueryInterface Method

Requests a pointer to a specified interface from a COM object.

Namespace: System.Runtime.InteropServices
Assembly: mscorlib (in mscorlib.dll)

public static int QueryInterface (
	IntPtr pUnk,
	ref Guid iid,
	out IntPtr ppv
public static int QueryInterface (
	IntPtr pUnk, 
	/** @ref */ Guid iid, 
	/** @attribute OutAttribute() */ /** @ref */ IntPtr ppv
JScript does not support passing value-type arguments by reference.



The interface to be queried.


A Guid, passed by reference, that is the interface identifier (IID) of the requested interface.


When this method returns, contains a reference to the returned interface.

Return Value

An HRESULT that indicates the success or failure of the call.

The QueryInterface method exposes the IUnknown::QueryInterface of a COM object, which attempts to obtain a specific interface pointer. Using QueryInterface on a COM object is the same as performing a cast operation in managed code. Calling an object with this method causes the reference count to increment on the interface pointer before the pointer is returned. Always use Marshal.Release to decrement the reference count once you have finished with the pointer. To obtain an IntPtr value that represents a IUnknown interface pointer, you can call Marshal.GetComInterfaceForObject, Marshal.GetIUnknownForObject, or Marshal.GetIDispatchForObject.


This method uses SecurityAction.LinkDemand to prevent it from being called from untrusted code; only the immediate caller is required to have SecurityPermissionAttribute.UnmanagedCode permission. If your code can be called from partially trusted code, do not pass user input to Marshal class methods without validation. For important limitations on using the LinkDemand member, see Demand vs. LinkDemand.

Windows 98, Windows 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

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

.NET Framework

Supported in: 2.0, 1.1, 1.0

.NET Compact Framework

Supported in: 2.0

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