Question

i’m marshaling ‘unmanaged c’ code to my C# code given below.

    [DllImport("ContainerDll.dll", CallingConvention = CallingConvention.Cdecl)]
    public static extern IntPtr NodeSearch(IntPtr firstNode, string key);

    IntPtr firstNode = IntPtr.Zero;

    private void button4_Click(object sender, EventArgs e)
    {
        IntPtr ret = NodeSearch(firstNode, "key_string");
    }

    //NodeSearch method will be called which is present in 'ContainerDll.dll'
    //pointer to structure will be returned.

    //my c-structure contains these fields. 

    //        typedef struct container
    //        {
    //             char Name[20];
    //             void *VoidData;
    //             struct container *Link;
    //        }       
    //             Node;

My C# variable ‘ret’ of type ‘IntPtr’ got the pointer to this structure now. It has the address returned from ‘NodeSearch’ method.

How to access this in C# form application(also in console application)?

I think I cannot use like this: ret->Name[0], ret->VoidData etc.

I am a beginner! Can you please me?

Answer 1

You will need to create a compatible struct definition in C#, and use the Marshal class to marshal the pointer to the struct.

The struct definition might look like the following:

[StructLayout(LayoutKind.Sequential)]
struct Container
{
    [MarshalAs(UnmanagedType.ByValTStr, CharSet = CharSet.Ansi, SizeConst = 20)]
    string Name;
    IntPtr VoidData;
    IntPtr Link
}

You should then be able to Marshal the pointer to this struct in a fashion similar to the following:

var ret = NodeSearch(IntPtr.Zero, "key_string");
var retContainer = (Container)Marshal.PtrToStructure(ret, typeof(Container));

In order to retrieve the link, or the void data, you would also need to call Marshal.PtrToStructure.