How to call managed code from unmanaged code?

Question

I want to call my .NET code from unmanaged C++. My process entrypoint is .NET based, so I don't have to worry about hosting the CLR. I know it can be done using COM wrappers for .NET objects, but I would like to access individual static methods of managed classes, so COM isn't my shortest/easiest route.

Answer 1

Take a look at the GCHandle class and the gcroot keyword, which provides a typesafe, templated wrapper around GCHandle.

You can use these to hold a reference to a CLR object (or a boxed value) in native code.

MSDN has a basic tutorial here.

Answer 2

Look at this solution: https://sites.google.com/site/robertgiesecke/Home/uploads/unmanagedexports The solution allows to call C# function from C by decorating your function with [DllExport] attribute (opposite of P/Invoke DllImport).

Exmaple:

C# code

class Test
{
     [DllExport("add", CallingConvention = CallingConvention.StdCall)]
     public static int Add(int left, int right)
     {
         return left + right;
     } 
}

C code:

 extern "C" int add(int, int);

 int main()
 {
      int z = add(5,10);
      printf("The solution is found!!! Z is %i",z);
      return 0;
 }

Output:

The solution is found!!! Z is 15

Update: There is a question and a good answer in comments:

How do I include the dll in the unmanaged project?

You have to link to the .lib file that is generated upon compiling your C# code (https://msdn.microsoft.com/en-us/library/ba1z7822.aspx?f=255&MSPPError=-2147217396)