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POMarshalling non-Blittable Structs from C# to C++
 

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  1. POMarshalling non-Blittable Structs from C# to C++
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    <p>I'm in the process of rewriting an overengineered and unmaintainable chunk of my company's library code that interfaces between C# and C++. I've started looking into P/Invoke, but it seems like there's not much in the way of accessible help.</p> <p>We're passing a struct that contains various parameters and settings down to unmanaged codes, so we're defining identical structs. We don't need to change any of those parameters on the C++ side, but we do need to access them after the P/Invoked function has returned.</p> <p>My questions are:<ol> <li> What is the best way to pass strings? Some are short (device id's which can be set by us), and some are file paths (which may contain Asian characters) <li> Should I pass an IntPtr to the C# struct or should I just let the Marshaller take care of it by putting the struct type in the function signature? <li> Should I be worried about any non-pointer datatypes like bools or enums (in other, related structs)? We have the treat warnings as errors flag set in C++ so we can't use the Microsoft extension for enums to force a datatype. <li> Is P/Invoke actually the way to go? There was some Microsoft documentation about Implicit P/Invoke that said it was more type-safe and performant. </ol></p> <p>For reference, here is one of the pairs of structs I've written so far:</p> <p>C++ </p> <pre class="lang-c prettyprint-override"><code>/** Struct used for marshalling Scan parameters from managed to unmanaged code. */ struct ScanParameters { LPSTR deviceID; LPSTR spdClock; LPSTR spdStartTrigger; double spinRpm; double startRadius; double endRadius; double trackSpacing; UINT64 numTracks; UINT32 nominalSampleCount; double gainLimit; double sampleRate; double scanHeight; LPWSTR qmoPath; //includes filename LPWSTR qzpPath; //includes filename }; </code></pre> <p>C#</p> <pre class="lang-cs prettyprint-override"><code>/// &lt;summary&gt; /// Struct used for marshalling scan parameters between managed and unmanaged code. /// &lt;/summary&gt; [StructLayout(LayoutKind.Sequential)] public struct ScanParameters { [MarshalAs(UnmanagedType.LPStr)] public string deviceID; [MarshalAs(UnmanagedType.LPStr)] public string spdClock; [MarshalAs(UnmanagedType.LPStr)] public string spdStartTrigger; public Double spinRpm; public Double startRadius; public Double endRadius; public Double trackSpacing; public UInt64 numTracks; public UInt32 nominalSampleCount; public Double gainLimit; public Double sampleRate; public Double scanHeight; [MarshalAs(UnmanagedType.LPWStr)] public string qmoPath; [MarshalAs(UnmanagedType.LPWStr)] public string qzpPath; } </code></pre>
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    1. COWhat exactly is not working. Using terms non-bittable is strange, because the structure you list, certainly be turned into a byte array. I would define the length of each field in the structure.
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    2. COI'm more looking for the correct design patterns for using P/Invoke. I thought anything with pointers is non-blittable?
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