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DllImportAttribute::PreserveSig Field

Indicates whether unmanaged methods that have HRESULT or retval return values are directly translated or whether HRESULT or retval return values are automatically converted to exceptions.

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

Set the PreserveSig field to true to directly translate unmanaged signatures with HRESULT or retval values; set it to false to automatically convert HRESULT or retval values to exceptions. By default, the PreserveSig field is true.

When true, the resulting method signature returns an integer value that contains the HRESULT value. In this case, you must manually inspect the return value and respond accordingly in your application.

When you set the PreserveSig field to false, the resulting method signature contains a void return type instead of an integer (HRESULT) return type. When the unmanaged method produces an HRESULT, the runtime automatically ignores a return value of S_OK (or 0) and does not throw an exception. For HRESULTs other than S_OK, the runtime automatically throws an exception that corresponds to the HRESULT. Note that the DllImportAttribute attribute only performs this conversion to methods that return an HRESULT.

You might decide to change the default error reporting behavior from HRESULTs to exceptions in cases where exceptions better fit the error reporting structure of your application.

This field is similar to the PreserveSigAttribute; however, in contrast to the PreserveSig field, the default value for the attribute is false.

In some cases, Visual Basic developers use the DllImportAttribute, instead of using the Declare statement, to define a DLL function in managed code. Setting the PreserveSig field is one of those cases.

The following code example uses the DllImportAttribute to import the unmanaged SHAutoComplete function once with the PreserveSig field set to true and again with the PreserveSig field set to false. This code example causes the SHAutoComplete function to generate any errors with an exception one time and an HRESULT the next.

No code example is currently available or this language may not be supported.

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Portable Class Library

Supported in: Portable Class Library

.NET for Windows Store apps

Supported in: Windows 8

.NET for Windows Phone apps

Supported in: Windows Phone 8.1, Windows Phone 8, Silverlight 8.1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

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

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