14.2. Cross-Unix Portability
The preceding section discussed issues related to the C language. This section focuses on 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, significant differences between systems can still affect portability.
This book does not discuss portability to older Unix systems that 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 autoconf, and in the 'configure.in' files of older programs that use autoconf.