SAFEARRAY data to unsigned char*

Question

I am trying to convert a SAFEARRAY data pointer to unsinged char*. However I am not getting the expected data. Here is a snippet.

SafeArrayLock(psaFrameData);
psaFrameData->rgsabound->cElements;
int nCount = psaFrameData->rgsabound->cElements -   psaFrameData->rgsabound->lLbound + 1;
frameData = new unsigned char[nCount];
memset(frameData, 0, nCount);

for (int i = 0; i < nCount; ++i)
{
    frameData[i] = ((unsigned char*)(psaFrameData)->pvData)[i];
}    
SafeArrayUnlock(psaFrameData);

@Anders just tried with cElements as size, but there is no difference. I am just asking if it's a correct way to transform the SAFEARRAY. — Ilian Zapryanov, Jun 21 '19 at 11:36
Is your safearray really of VT_UI1 type? If yes, just run `CopyMemory(frameData, psaFrameData->pvData,psaFrameData->rgsabound->cElements)` — Simon Mourier, Jun 21 '19 at 12:28
What data do you expect, and what do you observe instead? How is `psaFrameData` populated in the first place? — Igor Tandetnik, Jun 21 '19 at 12:44

score 0 · Accepted Answer · answered Jun 21 '19 at 22:53

Do not manually lock the array and then access its pvData (or any of its other data members) directly. Use the various accessors functions instead, such as SafeArrayAccessData():

Increments the lock count of an array, and retrieves a pointer to the array data.

Try something more like this:

// safety check: make sure the array has only 1 dimension...
if (SafeArrayGetDim(psaFrameData) != 1)
{
    // handle the error ...
}
else
{
    // safety check: make sure the array contains byte elements...
    VARTYPE vt = 0;
    SafeArrayGetVartype(psaFrameData, &vt);
    if (vt != VT_UI1)
    {
        // handle the error ...
    }
    else
    {
        // get a pointer to the array's byte data...
        unsigned char *data;
        if (FAILED(SafeArrayAccessData(psaFrameData, (void**)&data)))
        {
            // handle the error ...
        }
        else
        {
            // calculate the number of bytes in the array...
            LONG lBound, uBound;
            SafeArrayGetLBound(psaFrameData, 1, &lBound);
            SafeArrayGetUBound(psaFrameData, 1, &uBound);
            long nCount = uBound - lBound + 1; 

            // copy the bytes...
            frameData = new unsigned char[nCount];
            memcpy(frameData, data, nCount);

            // release the pointer to the array's byte data...
            SafeArrayUnaccessData(psaFrameData);
        }
    }
}

SAFEARRAY data to unsigned char*

1 Answers1