Declaring a C++ entry point in a PL/I routine has the same syntax as declaring another PL/I entry point. A C++ routine can be replaced by a PL/I routine without altering the PL/I code that calls the routine. Likewise, if a C++ routine calls a PL/I routine, the PL/I procedure contains no explicit declaration indicating control is being passed from the C++ routine. The declaration is contained within the C++ routine.

In C++, you must declare that the C++ entry point receives control from a PL/I routine. This declaration is in the form of an extern "PLI" linkage specification. The body of the C++ function is the same as if the routine were called from another C++ function. Calling a PL/I routine and being called by a PL/I routine are handled by the same extern "PLI" linkage specification.