I'm attempting to upgrade code written w/ VC++ 6.0 to .NET.  I'm aware of
most of the "major" changes from 6.0 to .NET, but subtle changes keep popping
up that I'm having difficulty finding documentation on.  

For example, several user defined classes store an ifstream data member.  In
the copy constructor, the assignment operator is used to copy an ifstream
reference passed into the constructor into the class' ifstream data member.  
In 6.0 this appears to have been acceptable (although perhaps not valid), but
in .NET it results in a compile-time error (operator= not defined for
ifstream object).

Two questions...is my observation on the ifstream assignment operator
correct?  And, is there a good resource where such subltle changes may be
documented for upgrading 6.0 code to .NET?

Thanks for your help in advance!