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)

val mutable PreserveSig : bool

Field Value

Type: System.Boolean

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.

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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