Passing parameters from c# to c++

Question

As the topic says, trying to pass a struct from c# environnement to c++.

c++ code that defines both the struct and the interface:

#pragma pack(push, 4)
    struct CEA708CONFIG 
    {
        BYTE                b608Service;            
        BYTE                bCompactStream;         
        BYTE                pActiveServices[63];    
        LONG                lActiveServiceCount;    //
        POINT               ptAlignmentPosition;    
    };
    #pragma pack(pop)


        interface
        __declspec(uuid("{some clsid}"))
        ICEA708Decoder : IUnknown {
            virtual HRESULT SetConfig(IN const CEA708CONFIG* pConfig) = 0;
            virtual HRESULT GetConfig(OUT CEA708CONFIG* pConfig) = 0;
        };

now to the c# code, i defined the same struct in c#

  [StructLayout(LayoutKind.Sequential, Pack = 4), Serializable]
    public struct CEA708CONFIG
    {
        public byte is608Service;
        public byte isCompactStream;
        //[MarshalAs(UnmanagedType.SafeArray, SafeArraySubType = VarEnum.VT_UI1)]
        [MarshalAs(UnmanagedType.ByValArray, SizeConst = 63)]
        public IntPtr activeServices;
        public long activeServiceCount;
        public Point alignmentPosition;
    };

and the corresponding interface that accepts the config structure

[ComVisible(true), ComImport, Guid("same clsid as above"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface ICEA708Decoder
{
    [return: MarshalAs(UnmanagedType.I4)]
    [PreserveSig]
    int SetConfig([In, MarshalAs(UnmanagedType.Struct)] ref CEA708CONFIG config);
    [return: MarshalAs(UnmanagedType.I4)]
    [PreserveSig]
    int GetConfig([Out, MarshalAs(UnmanagedType.Struct)] out CEA708CONFIG config);
    }

my problem occurs whenever i try to pass the structure, i can clearly see that while executing the c# code the entire struct is intialized with "reasonable" values, but once passed to the c++, i see that something has happened during the transaction.

the c# code that makes the magic happen:

            CEA708CONFIG   cc708Config;
            ICEA708Decoder CC708DecoderConfig = CC708Filter as ICEA708Decoder;

            if (CC708DecoderConfig == null)
            {
                throw new ApplicationException("Couldn't get ICEA708Decoder structure");
            }

            byte[] dataByte = new byte[63];
            int    size     = Marshal.SizeOf(dataByte[0]) * dataByte.Length;
            IntPtr pnt      = Marshal.AllocHGlobal(size);

            dataByte[0] = 1;
            Marshal.Copy(dataByte, 0, pnt, dataByte.Length);
            cc708Config.activeServices = pnt;
            if (0 != (hr = CC708DecoderConfig.SetConfig(ref cc708Config)))
            {
                throw new ApplicationException("Couldn't SetConfig() because: " + DirectShowLib.DsError.GetErrorText(hr));
            }

and the exception triggered by the SetConfig is:

{"Cannot marshal field 'activeServices' of type 'CCReIndexer.Graphs.CEA708CONFIG': Invalid managed/unmanaged type combination (Int/UInt must be paired with SysInt or SysUInt).":""}

thanks for your help!!

That field must be byte[]. And MarshalAs(UnmanagedType.Struct) is wrong, delete it. — Hans Passant
– Hans Passant, Commented Aug 6, 2012 at 12:54
when i change it back to byte[] im not able to compile the example above as there are typs mismatch conversions — igal k
– igal k, Commented Aug 6, 2012 at 12:59
i managed to convert the array to be a fixed size array, but this still produces me a garbage object. — igal k
– igal k, Commented Aug 6, 2012 at 13:48

Stas Bushuev · Accepted Answer · 2012-08-06 12:32:14Z

2

Have you tried transfer array as array?

[StructLayout(LayoutKind.Sequential, Pack = 4), Serializable]
public struct CEA708CONFIG
{
    public byte is608Service;
    public byte isCompactStream;
    [MarshalAs(UnmanagedType.ByValArray, SizeConst = 63)]
    public byte[] activeServices;
    public long activeServiceCount;
    public Point alignmentPosition;
};

byte[] dataByte = new byte[63];
cc708Config.activeServices = dataByte;

answered Aug 6, 2012 at 12:32

Stas Bushuev

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