Cannot cast C# enum to C++ enum when enum is in third assembly

Question

I've got a C# class:

public class MyManagedClass
{
  public ManagedEnum EnumValue {get; set;}
}

which uses the C# enum

public enum ManagedEnum
{
  Enum1,
  Enum2
}

This is accessed by a C++/CLI wrapper class and enum:

enum NativeEnum
{
  Enum1,
  Enum2
};

class WrapperClass
{
public:
  WrapperClass(ManagedNamespace::MyManagedClass^ inManaged):
    _Managed(inManaged)
  {}

  NativeEnum GetEnumValue()
  {
    return (NativeEnum)_Managed->EnumValue;
  }

private:
    gcroot<ManagedNamespace::MyManagedClass^> _Managed;
};

Now, as long as the C# class and C# enum are in the same assembly, this works fine.

But if the C# enum is in a different C# assembly, the C# class still builds fine, but trying to compile the C++ class yields the error:

error C2440: 'type cast' : cannot convert from 'OtherNamespace::ManagedEnum' to 'OtherNamespace::NativeEnum'
1>          Conversion requires a constructor or user-defined-conversion operator, which can't be used by const_cast or reinterpret_cast

Aaron Peavy · Accepted Answer · 2014-11-14 14:49:38Z

1

Try deriving the underlying value, then cast to the native enum.

This is a crude way of doing it, but may be sufficient in your case.

NativeEnum someMethod(ManagedEnum myEnum)
{
  return (NativeEnum)(int)myEnum;
}

Another way is to create a native template method taking both types and the managed enum input, and returning the native type. In such a case, you would have to use reflection to ascertain the underlying type of the managed enum.

edited Nov 14, 2014 at 14:49

answered Nov 14, 2014 at 14:21

Aaron Peavy

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3 Comments

Konstantin Yovkov Over a year ago

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient reputation you will be able to comment on any post.

Aaron Peavy Over a year ago

Sorry, I am new to posting here and was editing the post as you were commenting on it...

Aaron Peavy Over a year ago

Is your judgement because of how I worded the original sentence?

PortMan · Accepted Answer · 2014-11-14 15:29:06Z

1

In trying out Aaron P's answer, I discovered that the problem was that my C++ project didn't have the C# assembly with the enums in it as a reference. Once I added that reference, it all worked fine.

answered Nov 14, 2014 at 15:29

PortMan

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