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Asked: 2026-05-29T07:55:33+00:00

I have the following function: bool __declspec(dllexport) COMS_HL7QueryAnswer(char *szZone,char* szMessage, char** o_szAnswer) And I’m

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I have the following function:

bool __declspec(dllexport) COMS_HL7QueryAnswer(char *szZone,char* szMessage, char** o_szAnswer)

And I’m PInvoking it from C# like this:

public static extern bool COMS_HL7QueryAnswer(string szZone,string szMessage, out StringBuilder szAnswer);

It’s working in Windows 2003 but I’m getting access violation exceptions in W2008 and looks like they happen in the boundary of the PInvoke. Any help will be great.

Thanks.

EDIT: Looks like the AccessViolationException happens in the PInvoke boundary because:

  1. I don’t have a callstack other than the C# function.
  2. When I go with the debugger I can F10 until the last C++ function and when I exit the } then I go to the C# exception handler.
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1 Answer

  1. Editorial Team

    You’ll need to use

    [DllImport(CallingConvention = CallingConvention.Cdecl)]
public static extern bool COMS_HL7QueryAnswer(string szZone,string szMessage, out IntPtr szAnswer);

    Because p/invoke has no idea how to correctly free *o_szAnswer, you’ need to keep the pointer and pass it to the correct deallocation function yourself, after retrieving the data.

    If you are allowed to change the C++ side, there are a number of things you can do to make this more p/invoke-friendly. Or you can use a C++/CLI layer.

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