The 32-bit application programming interfaces (APIs) supported in the 64-bit operating environment are the same as the APIs supported in the 32-bit operating environment. Thus, no changes are required for 32-bit applications between the 32-bit environment and 64-bit environment. However, recompiling as a 64-bit application can require cleanup. See the rules that are defined in Chapter 4, Converting Applications for guidelines on how to clean up code for 64-bit applications.
The default 64-bit APIs are basically the UNIX 98 family of APIs. Their specification is written in terms of derived types. The 64-bit versions are obtained by expanding some of the derived types to 64-bit quantities. Correctly written applications that use these APIs are portable in source form between the 32-bit environment and 64-bit environment. The UNIX 2001 API family is also available in Solaris 10, see standards(5).