PInvoke C#: Function takes pointer to function as argument

Question

I'd like to access this function in my c# code, is this possible? so in the end the c++ code would call my function and also apply the struct called "sFrameofData".

C++ Code:

//The user supplied function will be called whenever a frame of data arrives.
DLL int Cortex_SetDataHandlerFunc(void (*MyFunction)(sFrameOfData* pFrameOfData));

Would this work perhaps?

C# Code:

[DllImport("Cortex_SDK.dll")]
public extern static int Cortex_SetDataHandlerFunc(ref IntPtr function(ref IntPtr pFrameOfData) );

did you test this? can't you try it yourself and tell us how it goes? — Davide Piras
– Davide Piras, Commented Mar 8, 2011 at 16:49

0xced · Accepted Answer · 2016-12-01 10:24:03Z

37

You want to use a delegate that matches the method signature of your "MyFunction" C++ method.

[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
public delegate void MyFunctionDelegate(IntPtr frame);

[DllImport("Cortex_SDK.dll")]
public extern static int Cortex_SetDataHandlerFunc(
[MarshalAs(UnmanagedType.FunctionPtr)]MyFunctionDelegate functionCallback);

edited Dec 1, 2016 at 10:24

0xced

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answered Mar 8, 2011 at 16:48

ahawker

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4 Comments

Hans Passant Over a year ago

Yup. [MarshalAs] is not needed here, it is already assumed. The frame argument is either ref or IntPtr, not both.

Tistatos Over a year ago

seems like i had issues with crashes unless i put the [UnmanagedFunctionPointer(CallingConvenction.Cdecl)] Thank you

felixh Over a year ago

I'd like to add that simply calling Cortex_SetDataHandlerFunc(MyFunc) where MyFunc is defined as void MyFunc(IntPtr frame) {...} isn't enough. Cortex_SetDataHandlerFunc(MyFunc) is essentially Cortex_SetDataHandlerFunc(new MyFunctionDelegate(MyFunc)) and the anonymous delegate object new MyFunctionDelegate(MyFunc) can be sometimes disposed by GC before MyFunctionDelegate returns. In this case you need to create a delegate object explicitly to avoid it to be GCed: var myDele = new MyFunctionDelegate(MyFunc); Cortex_SetDataHandlerFunc(myDele);

akshay dhule Over a year ago

Hi, I'm in similar situation where I have to pass method pointer in another method. I understood Marshaling part. how would you call this method now.

Community · Accepted Answer · 2017-05-23 10:29:50Z

1

I am not sure what is the proper way but I don't think is enough to use ref IntPtr for functions and structures...

see here for some help: C# P/Invoke: Marshalling structures containing function pointers

edited May 23, 2017 at 10:29

CommunityBot

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answered Mar 8, 2011 at 16:50

Davide Piras

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