c# - 将字节数组从 C# 传递到 C++ (COM)

Question

我正在尝试将一个字节数组从 c# 传递到 c++。我正在使用组件对象模型。这是我第一次体验 COM。如何将字节数组从 C# 传递到 C++？有什么建议吗？当我尝试传递二进制数组以外的其他类型(字符串、整数等)时没有问题

谢谢

我得到的错误

1-)error C2440: '=' : cannot convert from 'SAFEARRAY' to 'byte'     
2-)IntelliSense: no suitable conversion function from "SAFEARRAY" to "byte" exists  

这是我写的代码

C# 端，

public byte[] GetImage()
{

    try
    {

       SqlCommand command = new SqlCommand("this command returns Varbinary ", conn);
       SqlDataAdapter dataAdapter = new SqlDataAdapter(command);
       ImgBlobDT = new DataTable("ImgBlobDT");
       dataAdapter.Fill(ImgBlobDT);
       DataRow dr = ImgBlobDT.Rows[0];
       imgBytes = (byte[])dr["ImgBinary"];

    }
    catch ()
    {
        //some codes
    }


    return imgBytes;

}

C++ 方面

CoInitialize(NULL);

IDBCPtr obj;

obj.CreateInstance(__uuidof(DBC));

byte bytesArr[] = obj->GetImage();

CoUninitialize();

Answer 1

您要么需要按照@KimKulling 的回答建议分配不安全内存，要么将数组作为适当标记的SafeArray 发送。下面摘录了一个演示三种不同方法的示例，并且 available on github .

C# 界面看起来像这样:

[ComVisible(true)]
[Guid("7FE927E1-79D3-42DB-BE7F-B830C7CD32AE")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface IImageProvider
{
    [return: MarshalAs(UnmanagedType.SafeArray, SafeArraySubType = VarEnum.VT_UI1)]
    byte[] GetImage(int foo);

    IntPtr GetImageAsUnmanaged(int foo, out int cbBuff);

    void GetImageAsUnmanagedPreallocated(int foo, ref int cbBuff, IntPtr pBuff);
}

使用 C# 服务器实现:

[ClassInterface(ClassInterfaceType.None)]
[ComVisible(true)]
[Guid("D133B928-A98B-4006-8B00-4AA09BD042E7")]
[ProgId("CSByteArrayServer.ImageProvider")]
public class ImageProvider : IImageProvider
{
    private const int E_INVALIDARG = unchecked((int)0x80070057);

    RNGCryptoServiceProvider crng = new RNGCryptoServiceProvider();

    [return: MarshalAs(UnmanagedType.SafeArray, SafeArraySubType = VarEnum.VT_UI1)]
    public byte[] GetImage(int foo)
    {
        return GetBytes();
    }

    private byte[] GetBytes()
    {
        byte[] data = new byte[500];
        crng.GetBytes(data);
        return data;
    }

    public IntPtr GetImageAsUnmanaged(int foo, out int cbBuff)
    {
        var data = GetBytes();

        var result = Marshal.AllocCoTaskMem(data.Length);
        Marshal.Copy(data, 0, result, data.Length);

        cbBuff = data.Length;
        return result;
    }

    public void GetImageAsUnmanagedPreallocated(int foo, ref int cbBuff, IntPtr pBuff)
    {
        var data = GetBytes();

        if (cbBuff < data.Length)
        {
            cbBuff = data.Length;
            throw Marshal.GetExceptionForHR(E_INVALIDARG);
        }

        cbBuff = data.Length;
        Marshal.Copy(data, 0, pBuff, data.Length);
    }
}

还有一个 C++ 客户端:

int main()
{
    CoInitialize(NULL);

    IImageProvider *pImgProvider;
    CoCreateInstance(__uuidof(ImageProvider), nullptr, CLSCTX_INPROC_SERVER, __uuidof(IImageProvider), (LPVOID*)&pImgProvider);

    int imageId = 0;

    // with SafeArray
    {
        SAFEARRAY *pSafeArray;
        auto hr = pImgProvider->GetImage(0, &pSafeArray);
        assert(hr == S_OK);
        CComSafeArray<BYTE> safeArray;
        safeArray.Attach(pSafeArray);
        ManipulateData(&safeArray);
        // CComSafeArray will free the memory allocated by pSafeArray
    }

    // with CoTaskMemAlloc
    {
        char *pData;
        int cbData;
        auto hr = pImgProvider->GetImageAsUnmanaged(0, (long*)&cbData, (long*)&pData);
        assert(hr == S_OK);

        ManipulateData(pData, cbData);
        CoTaskMemFree(pData);
    }

    // with caller allocate
    {
        int cbData;
        auto hr = pImgProvider->GetImageAsUnmanagedPreallocated(imageId, (long*)&cbData, (long)nullptr);
        assert(hr == E_INVALIDARG);

        char *pData = new char[cbData];
        hr = pImgProvider->GetImageAsUnmanagedPreallocated(imageId, (long*)&cbData, (long)pData);
        assert(hr == S_OK);

        ManipulateData(pData, cbData);

        delete[] pData;
    }

    system("pause");

    CoUninitialize();
    return 0;
}

void ManipulateData(char* pBuff, int cbBuff)
{
    char hash = 0;
    for (int i = 0; i < cbBuff; i++)
    {
        hash ^= pBuff[i];
    }

    std::cout << "Hash is " << +hash << std::endl;
}

void ManipulateData(CComSafeArray<BYTE> *pSafeArray)
{
    BYTE hash = 0;
    for (ULONG i = 0; i < pSafeArray->GetCount(); i++)
    {
        hash ^= pSafeArray->GetAt(i);
    }

    std::cout << "Hash is " << +hash << std::endl;
}