Comparing Objects

  When comparing two variables to see if both refer to the same object, the
  exact comparison operator (double equal, ==) must be used. The inexact
  comparison operator (single equal, =) will cause a runtime error, as will
  a 'not equal' (<> or !=). If you wish to check that two variables refer to
  different objects, it can be done as follows:

    IF !(obj1 == obj2)

  This is the standard behaviour of the Clipper language, and similarly
  applies to comparisons of arrays.

  When comparing an object with NIL, however, the 'not equal' operator can
  be used. For example:

    IF obj <> NIL

  This will work in all cases.

  The reason for this behavior is that such comparisons of objects are
  actually comparing references to objects (pointers). Asking whether one
  such reference is greater than or less than another is meaningless, in the
  Clipper environment. The inexact comparison operator is similarly
  meaningless.