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    <p>As far as I can tell, the default calling convention for Mono on Unix platforms is <code>cdecl</code>. Which presumably matches your C++ code. So I guess that's not the problem. Worth double-checking though. Perhaps specify the calling convention explicitly in your pinvoke.</p> <p>I don't understand why you are using <code>UnmanagedType.Struct</code> for the return value. So far as I can tell that is not correct. On .net that would result in the struct being marshalled as a <code>VARIANT</code> which is absolutely not what you want. I'm not sure whether <code>UnmanagedType.Struct</code> has any meaning for Mono pinvoke on Linux, but in any case it should not be present so you should remove it.</p> <p>Nor is there any need to name the entry point. So I'd simplify the p/invoke.</p> <pre><code>[DllImport("somelib.so")] public static extern some_struct some_function(); </code></pre> <p>The other obvious potential mismatch would be between your native and managed struct definitions. You said:</p> <blockquote> <p>As you can see, there are no parameters that need marshaling, so the problem isn't with data that is being passed in.</p> </blockquote> <p>That's true, but what about the return value being passed out. That needs marshalling too, and you've got to get it right. Without being able to see definitions of your struct types (both native and managed), we're in no position to judge. If you cannot show them here, then you'll have to check that they match.</p> <p>Finally, it is conceivable the your compiler and the pinvoke marshaller assume a different ABI for struct return values. That is always a grey area. I would always recommend simple types as return values and return your struct as an out parameter.</p> <p>If I had to bet, I'd say that the problem lies in the struct definitions, which sadly you have not shown.</p> <hr> <p><strong>Update</strong></p> <p>Your question edit indicates that you have problems with a function that has <code>void</code> return type. In which case the only sane conclusion is that the problem is in your native code and not in the p/invoke. To track this down further, you'll need to look at the native code.</p>
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    1. POUnmanaged library function fails when called from C# but not C++
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    1. USDavid Heffernan
    1. USDavid Heffernan
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    1. COI should have added that I have tried modifying the function to return void, both in C# and C++, but still get the same segfault. The function always fails long before any return value is created, so I have been ruling out any problems marshaling the return value. I plan on figuring out the return value problems once I can get the code to execute that far.
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    2. COYou should have added? If you believe that the return value doesn't matter, why is it even in the question? Is it possible that the problem is with the native code? How about you post an SSCCE? Otherwise you are unlikely to get any response different from mine.
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      1. USDavid Heffernan
    3. COI fully expect the problem to be with the native code, however I don't understand what to look for when it fails only when called from managed code. As far as I can tell, the native code looks fine. Once I know what's wrong, I may be able to modify the native code to fix the issue. I have tried reproducing the problem with an SSCCE (like initializing a std::vector on the unmanaged side), but have not been able to do so. Simple cases all work, many of the actual functions I'm calling do not. Thanks for the insights.
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