Threading with .NET and OpenCV?

Question

I am having trouble getting a thread to work with OpenCV. The problem is with the ThreadStart() part of my code. ``` public ref class circles { public: static void circleFind(bool isPhoto, const char * windowName1, const char * windowName2, const char * photoName) {(stuff)} }; int main(int argc, char* argv[]) { const char *windowName1; const char *windowName2; const char *photoName; windowName1 = "Find Circles"; windowName2 = "Gray"; photoName = "Colonies 3.jpg"; bool isPhoto = false; //circles(isPhoto, windowName1, windowName2, photoName); Thread^ circleThread = gcnew Thread( gcnew ThreadStart (&circles::circleFind(isPhoto, windowName1, windowName2, photoName) )); circleThread->Start(); area(isPhoto, photoName); return 0; } ``` This is not all of the code but the important part. The errors I get are: 1>..\..\..\..\..\..\..\Program Files (x86)\OpenCV\samples\c\circle dection.cpp(130) : error C2102: '&' requires l-value 1>..\..\..\..\..\..\..\Program Files (x86)\OpenCV\samples\c\circle…

Accepted Answer

The problem here is that you are trying to use a function for a `ThreadStart` delegate which has an incompatible signature. `ThreadStart` is a delegate which has no arguments and returns no value. You are trying to use a method though which takes 4 arguments. This won't work.

You'll need to instead pass in a method which takes no arguments.

To pass parameters in C++, your best bet is to create a new class which has all of the parameters as fields. Then give it a method which has no parameters and returns no value and use that as the `ThreadStart` target.

```
ThreadHelper^ h = gcnew ThreadHelper();
h->Param1 = someValue;
ThreadStart^ threadDelegate = gcnew ThreadStart( h, &ThreadHelper::DoMoreWork );
```

There is a full example of this on the `ThreadStart` documentation page

- http://msdn.microsoft.com/en-us/library/system.threading.threadstart.aspx

Threading with .NET and OpenCV?

Solution

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