15.2 Cross-Unix Portability
In the previous section, we discussed issues related to the C language. Here we will discuss the portability of C programs across different Unix implementations. All modern Unix systems conform to the POSIX.1 (1990 edition) and POSIX.2 (1992 edition) standards. They also all support the sockets interface for networking code. However, there are still significant differences between systems which can affect portability.
We will not discuss portability to older Unix systems which do not
conform to the POSIX standards. If you need this sort of portability,
you can often find some valuable hints in the set of macros defined by