c++ cli ref class array converted to pointer

Question

I am trying to write a managed wrapper class in order to perform interop and conversion for a native class. I wrote something similar to this in my interop library;

namespace MyNamespace {
    public ref class MyClass {
    public:
        static void MyMethod(double myArray[]);
    }
}

However when I reference this library from my C# application, the interface has changed. If I F12 on the class in C# I get the regenerated interface MyClass [from metadata] which looks like this;

namespace MyNamespace {
    public class MyClass {
        public static void MyMethod(double myArray*);
    }
}

Why did the compiler convert the array into a pointer? How can I get the compiler to correctly expose this argument as an array rather than a pointer?

If I want to use the class in this way then I would have to get a pointer to the managed array in an unsafe context, which I don't want to do.

Update

When I do typeof(double[]) in C# I get;

{Name = "Double[]" FullName = "System.Double[]"}
    Assembly: {mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089}
    AssemblyQualifiedName: "System.Double[], mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089"
    Attributes: Public | Sealed | Serializable
    BaseType: {Name = "Array" FullName = "System.Array"}
    ...}

So I understand the comments suggesting that I need a System.Array. However, my question still stands, how do I declare a System.Double[] array in the interop class? Simply putting MyMethod(System::Double[] myArray) doesn't work...

I could be wrong, but I believe I am correct. It's converted to a pointer, because the array in your C++ doesn't utilize System.Array for arrays, which C# does and in that case it just expects a pointer to the data instead. — Bauss
– Bauss, Commented Jan 3, 2017 at 12:13
If so, maybe you could replace the double[] argument by some .net array type. It should be possible to use such a type in C++/CLI — wkl
– wkl, Commented Jan 3, 2017 at 12:17
My problem is that System.Array is typeless. I want the argument to be interpreted as a double[] not a System.Array. — Steztric
– Steztric, Commented Jan 3, 2017 at 12:18
I understand that in the native world, arrays and pointers are synonymous. However, there is such thing as a managed double[] and it can be passed in an argument, so how do I get the ref class to expose it as a double [] instead of a double*? — Steztric
– Steztric, Commented Jan 3, 2017 at 12:25

Lucas Trzesniewski · Accepted Answer · 2017-01-03 12:41:14Z

6

Use cli::array<double>^ which is a managed array. The double something[] syntax will define an unmanaged array, which decays to a pointer in metadata.

See here for reference.

answered Jan 3, 2017 at 12:41

Lucas Trzesniewski

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3 Comments

Steztric Over a year ago

Thank you Lucas, that is more like what I am looking for. However, I tried replacing it and I get the message "a C++/CLI array type is not allowed here". It allows std::array but I don't thin that is what I am looking for...

Steztric Over a year ago

I tried using std::array. I have to specify the rank, such as array<double, 1>. This still doesn't work as I get a different error "incomplete type is not allowed".

Lucas Trzesniewski Over a year ago

@Steztric Are you sure you didn't omit the final ^? You may also try to drop the cli::. Unfortunately I don't have a compiler handy at the moment so I can't check myself. std::array is something entirely different, you can't use that from C#.

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