There are two sets of data types that you can pass between C++ and PL/I routines: data types passed by reference using C++ explicit pointers explicitly in the routine, and data types passed by value without using C++ explicit pointers.

By reference means the parameter itself is passed. A copy of the parameter is not made. Any changes to the parameter made by the called routine can alter the original parameter passed by the calling routine. By value means a copy of the parameter is passed. Any changes to the parameter made by the called routine cannot alter the original parameter passed by the calling routine.