Setting the Type Tag Field

VARIANT type variables have a type tag field vt that indicates the data type of the data. VARIANT type return values are returned by methods with the type tag field set to the data type of the return value. VARIANT type input parameters in a method call must have the type tag field set by the application to one of the supported values. The correspondence of parameter types to data types is as follows.

Parameter type	Data type
PROPTYPE_LONG	VT_I2 or VT_I4
PROPTYPE_DATE	VT_DATE
PROPTYPE_BINARY	VT_BSTR or (VT_BSTR | VT_BYREF)
PROPTYPE_STRING	VT_BSTR or (VT_BSTR | VT_BYREF)

 

The following example shows how to initialize the variant data types listed above.

HRESULT hr;
VARIANT vEMail;
VARIANT vNotBefore;
VARIANT vCount;
VARIANT vByRef;
BSTR bstr = NULL;
SYSTEMTIME st;

//Set the BSTR variant data type.
VariantInit(&vEMail);
vEMail.vt = VT_BSTR;   
vEMail.bstrVal = SysAllocString(L"someone@example.com");
if (NULL == vEMail.bstrVal)
{
    hr = E_OUTOFMEMORY;
    //Handle error.   
}
//Use the variant.
VariantClear(&vEMail);  //when done


//Set the BSTR|BYREF variant data type.
VariantInit(&vByRef);
vByRef.vt = VT_BSTR | VT_BYREF;   
vByRef.pbstrVal = &bstr;
//Use the variant.
VariantClear(&vByRef);  //when done
SysFreeString(bstr);


//Set the DATE variant data type.
memset(&st, 0, sizeof(SYSTEMTIME));
st.wYear = 2000;
st.wMonth = 1;
st.wDay = 1;
st.wHour = 12;

VariantInit(&vNotBefore);
vNotBefore.vt = VT_DATE;
if (!SystemTimeToVariantTime(&st, &vNotBefore.date))
{
    hr = E_FAIL;
    //Handle error.
}
//Use the variant.
VariantClear(&vNotBefore);  //when done


//Set the LONG variant data type.
VariantInit(&vCount);
vCount.vt = VT_I4;
vCount.long = 123456;
//Use the variant.
VariantClear(&vCount);  //when done