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15.2.2 Cross-Unix System Interfaces

There are several Unix system interfaces which have associated portability issues. We do not have the space here to discuss all of these in detail across all Unix systems. However, we mention them here to indicate issues where you may need to consider portability.

Many Unix systems provide the `curses' interface for simple graphical terminal access, but the name of the library varies. Typical names are `-lcurses' or `-lncurses'. Some Unix systems do not provide `curses', but do provide the `-ltermcap' or `-lterminfo' library. The latter libraries only provide an interface to the `termcap' file or `terminfo' files. These files contain information about specific terminals, the difference being mainly the manner in which they are stored.
`proc file system'
The `/proc' file system is not available on all Unix systems, and when it is available the actual set of files and their format varies.
`pseudo terminals'
All Unix systems provide pseudo terminals, but the interface to obtain them varies widely. We recommend examining the configuration of an existing program which uses them, such as GNU emacs or Expect.
`shared libraries'
Shared libraries differ across Unix systems. The GNU libtool program was written to provide an interface to hide the differences. See section 10. Introducing GNU Libtool.
The `termios' interface to terminals is standard on modern Unix systems. Avoid the older, non-portable, `termio' and `tty' interfaces (these interfaces are defined in `termio.h' and `sgtty.h', respectively).
Many, but not all, Unix systems support multiple threads in a single process, but the interfaces differ. One thread interface, pthreads, was standardized in the 1996 edition of POSIX.1, so Unix systems are likely to converge on that interface over time.
Most Unix systems maintain the `utmp' and `wtmp' files to record information about which users are logged onto the system. However, the format of the information in the files varies across Unix systems, as does the exact location of the files and the functions which some systems provide to access the information. Programs which merely need to obtain login information will be more portable if they invoke a program such as w. Programs which need to update the login information must be prepared to handle a range of portability issues.
`X Window System'
Version 11 of the X Window System is widely available across Unix systems. The actual release number varies somewhat, as does the set of available programs and window managers. Extensions such as OpenGL are not available on all systems.

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