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    <p> The exception "Cannot implicitly convert type 'void' to 'object'" is thrown when attempting to assign the result of a void method to a variable. While this is normally a compiler error, if it's seen during execution then it usually occurred as a result of dynamic invocation of a method (e.g. using the dynamic keyword or using a dynamic language like IronPython).</p> <p>.NET 4.5.1 introduced a overloads for <code>Marshal.SizeOf</code> and <code>Marshal.PtrToStructure</code> and dynamic method invocation may pick the new overload under certain circumstances. See Microsoft <a href="http://support.microsoft.com/kb/2909958" rel="nofollow">KB2909958</a>. The above exception wouldn't be coming from the P/Invoke itself, but from the subsequent marshaling operations.</p> <p>The easiest solution to these kinds of issues is to just introduce a cast within the call to ensure that the correct method is resolved.</p> <pre class="lang-cs prettyprint-override"><code>#Code from 4.5 dynamic dynamicVar = ... object boxedStruct = Marshal.PtrToStructure(myPtr, dynamicVar.GetType()); // Above resolves to 'object Marshal.PtrToStructure(IntPtr, Type)' in 4.5 // and resolves to 'void Marshal.PtrToStructure&lt;T&gt;(IntPtr, T)' in 4.5.1 int size = Marshal.SizeOf(dynamicVar.GetType()); // Above resolves to 'object Marshal.SizeOf(Type)' in 4.5 // and resolves to 'void Marshal.SizeOf&lt;T&gt;(T)' in 4.5.1 #Fixed for 4.5.1 dynamic dynamicVar = ... object boxedStruct = Marshal.PtrToStructure(myPtr, (Type)dynamicVar.GetType()); // Adding the cast forces the code to resolve to // 'object Marshal.PtrToStructure(IntPtr, Type)' int size = Marshal.SizeOf((Type)dynamicVar.GetType()); // Adding the cast forces the code to resolve to // 'int Marshal.SizeOf(Type)' </code></pre>
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    1. USXy Ziemba
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    1. COSolved my problem, and very pleased .Net authors picked this thread up so quickly!
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      1. USAlex
    2. CO@Xavier Are you saying that the actual error is in code that calls `PtrToStructure` and `SizeOf`, and that code is in Alex's app and not in the question? I'm just trying to understand.
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      1. USDavid Heffernan
    3. CO@DavidHeffernan: Yes. That's correct. The code is elsewhere in the app and is related to marshaling to/from P/Invoke calls.
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