The API specifies a set of functions that are
available to an application programmer, including the parameters that are
passed to each function and the return values the programmer can expect.
Three of the most common APIs available to application programmers are
theWindows API forWindows systems, the POSIX API for POSIX-based systems
(which include virtually all versions of UNIX, Linux, andMac OSX), and the Java
API for programs that run on the Java virtual machine. A programmer accesses
an API via a library of code provided by the operating system. In the case of
UNIX and Linux for programs written in the C language, the library is called
libc. Note that—unless specified—the system-call names used throughout
this text are generic examples. Each operating system has its own name for
each system call