Retrieve the data associated with a general constraint of type EXP. Calling this method for a general constraint of a different type leads to an exception. You can query the GenConstrType attribute to determine the type of the general constraint.
See also addGenConstrExp for a description of the semantics of this general constraint type.
genc: The general constraint object.
Any of the following arguments can be NULL.
xvarP: Pointer to store the variable.
yvarP: Pointer to store the variable.