Question

While using VariantCopy method, I come across the following compile error:

error C2664: 'VariantCopy' : cannot convert parameter 2 from 'const VARIANT *' to 'VARIANTARG *'

Is there any way to solve this error? Do I need to include any preprocessor directive or library?

Answer 1

The signature of VariantCopy used to be

HRESULT VariantCopy( 
  VARIANTARG FAR* pvargDest, 
  VARIANTARG FAR* pvargSrc 
); 

It is strange, but the input parameter is not const, you should be aware of that in your code.

MSDN documentation explains why. The function might modify pvargSrc

If pvargSrc is a VT_DISPATCH or VT_UNKNOWN, AddRef is called to
increment the object’s reference count.

Update

In the most recent SDK, the 2nd parameter became const. However, I found this in MFC sources:

static HRESULT copy(_Out_ VARIANT* p1, _In_ const VARIANT* p2) 
{
    p1->vt = VT_EMPTY; 
    return VariantCopy(p1, const_cast<VARIANT*>(p2));
}