Wrapping native C++ struct in C++/CLI

Question

I've never worked with either C++ or C++/CLI, but I would like to use a native C++ library in a C# project. I googled a bit, learnt a few things about C++/CLI and decided to give it a head start. But I'm not sure if I'm doing any of it right.

I have the following struct in a native namespace:

avcodec.h

typedef struct AVCodecDescriptor {
    enum AVCodecID     id;
    enum AVMediaType type;

    const char      *name;
    const char *long_name;
    int             props;
} AVCodecDescriptor;

Now I want to wrap this struct in C++/CLI for using it in C#:

public ref struct AVCodecDescriptorWrapper {

    private:
        struct AVCodecDescriptor *_avCodecDescriptor;

    public:
        AVCodecDescriptorWrapper() {
            _avCodecDescriptor = new AVCodecDescriptor();
        }
        ~AVCodecDescriptorWrapper() {
            delete _avCodecDescriptor;
        }

        // what do?
        property AVCodecID Id {
            AVCodecID get() {
                return; // what comes here ????
            }
        }

};

However, it seems like I'm doing something horribly wrong since I'm not even able to see the fields of the struct AVCodecDescriptor in C++/CLI. Do I have to wrap the enums in the struct to? Do I have to copy them into C++/CLI and cast it (well, enum AVCodecID has like 350 values - a copy/paste seems ridiculus.)

Answer 1

You need to create a equivalent CLI class of native struct and Enums.

public ref class ManagedAVCodecDescriptor {
    ManagedAVCodecIDClass id;
    ManagedAVMediaTypeClass type;

    String^ name;
    String^ long_name;
    int props;
};

Enum equivalent class will look like this:

public enum class ManagedAVCodecIDClass
{
    xyx = 1,
    abc = 2,
    ...
}

Now in your AVCodecDescriptorWrapper you should get AVCodecDescriptor object and put all information in the ManagedAVCodecDescriptor object and pass it to C# class.

ManagedAVCodecDescriptor^ mObject = gcnew ManagedAVCodecDescriptor();
mObject.setSomeValue(nativeStruct->somevalue);

and pass mObject to C# code as general C# object.