Clears a variant.
Use this function to clear variables of type VARIANTARG (or VARIANT) before the memory containing the VARIANTARG is freed (as when a local variable goes out of scope).
The function clears a VARIANTARG by setting the vt field to VT_EMPTY. The current contents of the VARIANTARG are released first. If the vtfield is VT_BSTR, the string is freed. If the vtfield is VT_DISPATCH, the object is released. If the vt field has the VT_ARRAY bit set, the array is freed.
If the variant to be cleared is a COM object that is passed by reference, the vtfield of the pvargparameter is VT_DISPATCH | VT_BYREF or VT_UNKNOWN | VT_BYREF. In this case, VariantClear does not release the object. Because the variant being cleared is a pointer to a reference to an object, VariantClear has no way to determine if it is necessary to release the object. It is therefore the responsibility of the caller to release the object or not, as appropriate.
In certain cases, it may be preferable to clear a variant in code without calling VariantClear. For example, you can change the type of a VT_I4 variant to another type without calling this function. Safearrays of BSTR will have SysFreeString called on each element not VariantClear. However, you must call VariantClear if a VT_type is received but cannot be handled. Safearrays of variant will also have VariantClear called on each member. Using VariantClear in these cases ensures that code will continue to work if Automation adds new variant types in the future.
Do not use VariantClear on unitialized variants; use VariantInit to initialize a new VARIANTARG or VARIANT.
Variants containing arrays with outstanding references cannot be cleared. Attempts to do so will return an HRESULT containing DISP_E_ARRAYISLOCKED.