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I have a DLL written in C++, now I want to invoke the DLL in ASP.NET Web Application. How should I do?
The environment is Visual Studio 2008, C#.
Thank you!

It's called P/Invoke and uses System.Runtime.InteropServices and System.Runtime.InteropServices.DllImportAttribute.
You can find a simple code sample here:[^].

It may me fairly simple or quite tricky. To specify marshaling between native (unmanaged) and managed parameters you may also need to use the attribute System.Runtime.InteropServices.MarshalAsAttribute, see the code sample:[^].

In more complex cases (in particular, when memory allocation is involved), you may need to use explicit marshaling methods with the class System.Runtime.InteropServices.Marshal, see[^].

In even more complex cases you may need to use custom marshaling. See, for example:[^].


After changes in Microsoft documentation, most adequate link to P/Invoke and C++/CLI implicit P/Invoke is this:[^].

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flyicing 9-Jun-11 20:09pm    
Thank you for you details!
But now I encounter an error: cannot find the DLL, though I have put it under /bin folder. Bye the way, I also try to put it under Windows/systems32, but still error.
Sergey Alexandrovich Kryukov 10-Jun-11 11:39am    
OK, ***you*** cannot find DLL and think this is because my answer is not good enough, or something?
And did you voted 1 by this reason?
flyicing 12-Jun-11 9:12am    
Oh,my god! I am really sorry. I just don't know what that vote mean. Your answer is perfect, with so many details. I am sincerely thank you! Please forgive my fault! I am so Sorry!
Sergey Alexandrovich Kryukov 12-Jun-11 13:46pm    
No problem at all, mistakes happen; admitting them and decent respond to criticism is the virtue! Is you still have a problem, feel free to ask a follow-up questions, as people usually do.
Thanks for accepting this, answer, hope it helps.

Good luck, call again.
Maciej Los 9-Apr-15 15:01pm    
Sergey, why do you made some changes to this answer?
You can call in .net through api

Marshal.GetDelegateForFunctionPointer using this you can pass the parameter to the c++ function
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