如何访问从 C++ 中的 COM 对象返回的 VARIANT 数据类型中的 SAFE ARRAY？

Question

我正在使用 COM 对象。我调用 COM 对象的函数，此函数返回包含我的设备列表的 SAFE ARRAY 的 VARIANT 数据类型。我如何使用这个 VARIANT 来访问我的设备的 SAFEARRY。

  VARIANT namList; 
  SAFEARRAY* myequip;
  namList=str->GetNames();

Answer 1

为了在这样的 VARIANT 中使用 SAFEARRAY，您需要进行大量的验证和错误检查。这是您需要遵循的粗略模式。请仔细阅读评论，因为我对您使用的 COM API 做了一些假设。

// verify that it's an array
if (V_ISARRAY(&namList))
{
    // get safe array
    LPSAFEARRAY pSafeArray = V_ARRAY(&namList);

    // determine the type of item in the array
    VARTYPE itemType;
    if (SUCCEEDED(SafeArrayGetVartype(pSafeArray, &itemType)))
    {
        // verify it's the type you expect
        // (The API you're using probably returns a safearray of VARIANTs,
        // so I'll use VT_VARIANT here. You should double-check this.)
        if (itemType == VT_VARIANT)
        {
            // verify that it's a one-dimensional array
            // (The API you're using probably returns a one-dimensional array.)
            if (SafeArrayGetDim(pSafeArray) == 1)
            {
                // determine the upper and lower bounds of the first dimension
                LONG lBound;
                LONG uBound;
                if (SUCCEEDED(SafeArrayGetLBound(pSafeArray, 1, &lBound)) && SUCCEEDED(SafeArrayGetUBound(pSafeArray, 1, &uBound)))
                {
                    // determine the number of items in the array
                    LONG itemCount = uBound - lBound + 1;

                    // begin accessing data
                    LPVOID pData;
                    if (SUCCEEDED(SafeArrayAccessData(pSafeArray, &pData)))
                    {
                        // here you can cast pData to an array (pointer) of the type you expect
                        // (The API you're using probably returns a safearray of VARIANTs,
                        // so I'll use VARIANT here. You should double-check this.)
                        VARIANT* pItems = (VARIANT*)pData;

                        // use the data here.

                        // end accessing data
                        SafeArrayUnaccessData(pSafeArray);
                    }
                }
            }
        }
    }
}