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POWindows Structured Storage - 32-bit vs 64-bit COM Interop
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copied!<p>While attempting to convert an existing 32-bit application to 64-bit, I've run into trouble getting some COM Interop code to work properly. The code is accessing the structured storage API, using managed code I translated from the various Windows SDK header/IDL files.</p> <p>The code is failing when I try to call into <code>IPropertyStorage.ReadMultiple()</code>, with <code>STG_E_INVALIDPARAMETER</code>. The previous interop calls, to <code>StgOpenStorageEx</code> and <code>IPropertySetStorage.Open</code>, appear to work fine. MSDN claims this error means something's wrong with my PROPSPEC parameters, but the same parameter values work fine when compiled as a 32-bit application and the value I get back is the correct string value for the specified property.</p> <p>Here are what I think are the relevant bits:</p> <pre class="lang-cs prettyprint-override"><code>// PropertySpecKind enumeration. public enum PropertySpecKind : uint { Lpwstr = 0, PropId = 1 } // PropertySpec structure: [StructLayout(LayoutKind.Explicit)] public struct PropertySpec { [FieldOffset(0)] public PropertySpecKind kind; [FieldOffset(4)] public uint propertyId; [FieldOffset(4)] public IntPtr name; } // PropertyVariant Structure: [StructLayout(LayoutKind.Explicit)] public struct PropertyVariant { [FieldOffset(0)] public Vartype vt; [FieldOffset(8)] public IntPtr pointerValue; } // IPropertyStorage interface [ComImport] [Guid("00000138-0000-0000-C000-000000000046")] [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)] public interface IPropertyStorage { int ReadMultiple( uint count, [MarshalAs(UnmanagedType.LPArray, SizeConst = 0)] PropertySpec[] properties, [Out, MarshalAs(UnmanagedType.LPArray, SizeConst = 0)] PropertyVariant[] values); void WriteMultiple( uint count, [MarshalAs(UnmanagedType.LPArray, SizeConst = 0)] PropertySpec[] properties, [MarshalAs(UnmanagedType.LPArray, SizeConst = 0)] PropertyVariant[] values, uint miniumumPropertyId); } var properties = new PropertySpec[1]; properties[0].kind = PropertySpecKind.PropId; properties[0].propertyId = 2; var propertyValues = new PropertyVariant[1]; // This helper method just calls StgOpenStorageEx with appropriate parameters. var propertySetStorage = StorageHelper.GetPropertySetStorageReadOnly(fileName); var propertyStorage = propertySetStorage.Open(StoragePropertySets.PSGUID_SummaryInformation, StorageMode.Read | StorageMode.ShareExclusive); propertyStorage.ReadMultiple(1, properties, propertyValues); // Exception is here. </code></pre>

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