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POExported function in C++ COM DLL not found from C#
 

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  1. POExported function in C++ COM DLL not found from C#
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    <p>I have an existing COM DLL that is currently accessed (just one function) through a VB wrapper class and called from a C# class.</p> <p>I'm trying to add callbacks into my C# code (4 separate callbacks). My chosen approach is the only one that I've found but I'm having issues.</p> <p>It says "Unable to find an entry point named 'InitDotNet' in DLL 'xxxx'.</p> <h2>My DLL header file:</h2> <pre><code>extern "C" { #define DLL __declspec(dllexport) typedef void (__stdcall * CB_func1)(int); typedef void (__stdcall * CB_func2)(char *); DLL void InitDotNet(CB_func1 func1, CB_func2 func2); } ... class CComInterface : public CCmdTarget ... afx_msg void mainCall(short parm1, LPCTSTR parm2); ... </code></pre> <h2>My DLL C++ file:</h2> <pre><code>... CB_func1 func1Function; CB_func2 func2Function; ... IMPLEMENT_DYNCREATE(CComInterface, CCmdTarget) ... BEGIN_DISPATCH_MAP(CComInterface, CCmdTarget) DISP_FUNCTION(CComInterface, "mainCall", mainCall, VT_EMPTY, VTS_I2 VTS_BSTR) END_DISPATCH_MAP() ... IMPLEMENT_OLECREATE(CComInterface, "MyDll.Interface", ...) ... void CComInterface::mainCall(short parm1, LPCTSTR parm2) { ... // at various times call func1Functoin and func2Function ... } DLL void InitDotNet(CB_func1 func1, CB_func2 func2) { func1Function = func1; func2Function = func2; } </code></pre> <h2>My VB wrapper looks like this:</h2> <pre><code>Public Class MyWrapperClass Private Shared Protocol As Object = CreateObject("MyDll.Interface") Public Shared Sub mainCall(ByVal parm1 As Short, ByVal parm2 As String) Protocol.mainCall(parm1, parm2) End Sub End Class </code></pre> <h2>My C# code looks like this:</h2> <pre><code>... using System.Runtime.InteropServices namespace MyNamespace { public partial class MyForm : AnotherForm { ... [UnmanagedFunctionPointer(CallingConvention.StdCall)] public delegate void func1Callback(int value); [UnmanagedFunctionPointer(CallingConvention.StdCall)] public delegate void func2Callback(string value); [DllImport("mycppdll.dll")] public static extern void InitDotNet([MarshalAs(UnmanagedType.FunctionPtr)] func1Callback f1c, [MarshalAs(UnmanagedType.FunctionPtr)] func2Callback f2c); ... private void MyFunc() { func1Callback f1c = (value) =&gt; { // work here }; func2Callback f2c = (value) =&gt; { // work here }; InitDotNet(f1c, f2c); MyWrapperDll.MyWrapperClass.mainCall(1, "One"); } </code></pre> <p>Anybody have any thoughts on what I'm doing wrong?</p>
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    1. USIan Frisbie
    1. USIan Frisbie
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    1. COThis is not the cause of your entry-point error, but note that you need to retain a reference to the delegates stored in `f1c` and `f2c` for as long as the unmanaged code might call them. Otherwise, they may be garbage-collected before the unmanaged code invokes them. If the unmanaged code will not call them after `InitDotNet()` returns, then you need to call `GC.KeepAlive()` on both delegate objects after the `InitDotNet()` call. Otherwise, make sure you store them on a field somewhere.
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      1. UScdhowie
    2. COIt looks like the entrypoint you defined in your Dllimport statement isn't correct, or runtime can't find it for whatever reason. Are you familiar with dumpbin? If you run dumpbin /exports on the .dll in question, you can see what the entrypoint names actually are. Edit: or what cdhowie said. You can still check on the entrypoints though, just for completeness sake :)
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      1. USB L
    3. COCan you just confirm what DLL is defined to be in the declaration of InitDotNet?
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      1. USTheMathemagician
 

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