Marshalling a C structure to C#

Question

Hi, I don't know how to marshall this structure in Mono.

typedef struct rib_struct {
    rib_used_t used;
    rib_status_t status;
    rib_role_t role;
    uint8_t conf;
    rib_dc_t *pending;
    pthread_mutex_t mutex;
    pthread_cond_t cond;
    rib_f_t *props;
} rib_t;

And for example, rib_dc_t is like:

typedef struct rib_dc_struct {
    uint16_t id;
    uint8_t min_id;
    uint8_t conf;
    struct rib_dc_struct *next;
} rib_dc_t;

I don't know how to marshall the pthread structures. And the pointers... should I use IntPtr or a managed structures? How to mashall the pointer in the last struct to the struct itself?

Thanks in adanvaced

Answer 1

It doesn't come much more ickier than this. You'd be forced to declare the pthread_mutex_t and pthread_cond_t structures as well. Not great, these are implementation details that C# code shouldn't have to bother with. I would recommend you use the [StructLayout(LayoutKind.Explicit)] so you can declare only the members that the C# code needs. You'll have to write a little test program in C/C++ that uses offsetof() to find the member offsets.

The pointers need to be declared as IntPtr. You have to marshal the pointed-to values yourself with Marshal.PtrToStructure(). Not sure how much of this is covered by Mono.

Answer 2

Thanks for the answer Hans. I have finally managed to avoid this structure, so no problem.

There are only some functions left I dont know how to marshall.

int rib_init(rib_callbacks_t *cb, void *data);

rib_callbacks_t is a structure of delegates like this:

    [StructLayout(LayoutKind.Sequential)]
    internal struct rib_callbacks_t 
    {
        public NewDevConnectedCallback new_dev_connected;
        public DevDisconnectedCallback dev_disconnected;
        public DcConnectedCallback new_dc_connected;
    }

rib_feature_t *rib_register_feature(char *desc);

I should return this method as IntPtr to unmarshall with Marshall.IntPtrToStructure, am i wrong?

rib_feature_t **rib_register_many_features(uint16_t *dev_type, char **desc, int count);

This One I don't know how to marshall. The two ** have broken me :(.

int rib_send(rib_dc_t *dc, const void *msg, size_t len); int rib_recv(rib_dc_t *dc, void *buf, size_t len);

In these ones, I have used [MarshalAs(UnmanagedType.LPArray)]byte[] buf/msg... is this ok?

Regards