In programming languages, the name space is defined as the portion of a load module within which a particular declaration applies or is known. Within the same load module, the name space of external data under both PL/I and C is the same. Therefore, PL/I's and C's external data map to each other, provided that the C routine is non-reentrant or naturally reentrant.

Figure 1. Name space of external data in PL/I static call to C

Figure 1 illustrates that within the same load module, the name spaces of PL/I and C routines are the same. Therefore you can give external data the same name in a PL/I to C application, if no load module boundary is crossed.