How to translate a C++ method with VARIANT to C# without VARIANT?

Question

I've never worked with variants in C++. But I'm maintaining code from old C++ projects. Part of it is to translate it or part of it into C#.

I found methods that use variants. I want to "kill" any variant use in a new project version. Can someone help me out on how? Based on this example maybe? Also I'm not a C++ expert. I would like to know what this method is doing (Obviously converting variant to byte array. But how exactly? Where is the data etc.?)

(Example) Method:

protected bool ConvertVariantToByteArray(VARIANT vtData, int lCount, BYTE[] pArray)
{
    if (vtData.vt != (VARENUM.VT_ARRAY | VARENUM.VT_UI1))
        return false;
    BYTE[] pSafeArrayData;
    if (FAILED(SafeArrayAccessData(vtData.parray, (void**) &pSafeArrayData)))
    {
        return false;
    }
    long lLbound;
    if (FAILED(SafeArrayGetLBound(vtData.parray, 1, &lLbound)))
    {
        SafeArrayUnaccessData(vtData.parray);
        return false;
    }
    long lUbound;
    if (FAILED(SafeArrayGetUBound(vtData.parray, 1, &lUbound)))
    {
        SafeArrayUnaccessData(vtData.parray);
        return false;
    }
    if (lCount < lUbound - lLbound + 1)
    {
        lCount = lUbound - lLbound + 1;
        SafeArrayUnaccessData(vtData.parray);
        return false;
    }
    for (long i = lLbound; i < lUbound + 1; ++i)
    {
        *pArray++ = *pSafeArrayData++;
    }
    SafeArrayUnaccessData(vtData.parray);
    lCount = lUbound - lLbound + 1;
    return true;
}

Larger context:

The application reads/writes via Falcon library to/from EIB/KNX bus. Seems the data passed to/from the bus is of VARIANT data type.

Variants are used with COM objects. If you are using COM, then you may have to use variants. What's the larger context of your question? — Lubo Antonov, Feb 23 '15 at 11:33
Did you have a look here? -> http://stackoverflow.com/questions/15806733/variant-datatype-of-c-into-c-sharp — Manuel Barbe, Feb 23 '15 at 11:34
It mostly corrupts memory, the caller does not have good odds at guessing at the required size of pArray. Do not use it. Converting a variant to byte[] in C# is trivial, just cast it. — Hans Passant, Feb 23 '15 at 11:36

score 1 · Answer 1 · answered Feb 23 '15 at 11:34

VARIANT is a COM thing rather than a C++ thing. You may not need to translate this method verbatim if you are moving away from variants.

A VARIANT can stores (alomst) anything, including other VARIANTS. The code you have shown converts a VARIANT to an array of bytes.

The array has a lower and upper bound (lbound and ubound in this sample) - they do no need to run from 0 up. The for loop is copying the data into the array.

You can call COM from C#, so may not need to translate the code.

How to translate a C++ method with VARIANT to C# without VARIANT?

1 Answers1