VARIANT and CComVariant

CComVariant is a C++ encapsulation of VARIANT.

They are more or less tagged unions.

An example of using CComVariant when programming in Inventor is in the many get_Item calls in for loops:

   const int ikNumConstraints = pConstraintList->Count ;

   for (int j = 1 ; j <= ikNumConstraints ; j++) {

       CComPtr<AssemblyConstraint> pConstraint;

       hRes = pConstraintList->get_Item(CComVariant(j),&pConstraint) ;

       if (FAILED(hRes)) {

           TRACE (L"Could not get the constraint %d of the assembly, hr=%X\n",j,hRes);

           return ;

       }

       TRACE (L"Got constraint %d\n",j);

   }

Look at that CComVariant(j) call. That is how you send an integer to get_Item when get_Item wants a VARIANT.

Note also that it all the get_Item things start at 1.

You can create an empty variant and a real double variant as illustrated below:

CComVariant varEmpty, varReal(0.0);

Or you can use a global constant empty variant like this.