9.2 The System Library: libSystem

In Darwin, much is built into the system library, /usr/lib/libSystem.dylib . In particular, the following libraries are included in libSystem :


The standard C library. This library contains the functions used by C programmers on all platforms.


The NetInfo library.


The kernel virtual memory library.


The math library, which contains arithmetic functions.


The POSIX threads library, which allows multiple tasks to run concurrently within a single program.


This library provides functions, such as dlopen( ) , that interface to the dynamic linker using the native dyld , NSModule , and NSObjectFileImage functions.


Database routines.

Symbolic links are provided as placeholders for these libraries. For example, libm.dylib is a symbolic link in /usr/lib that points to libSystem.dylib . Thus, - lm or - lpthread do no harm, but are unnecessary. The - lm option links to the math library, while - lpthread links to the POSIX threads library. Since libSystem provides these functions, you don't need to use these options. However, you should use them to make sure your application is portable to other systems. (Since libm . dylib and libpthread.dylib are symbolic links to libSystem.dylib , the extra - l options refer to the same library.)

In Mac OS X 10.1 and earlier versions, the curses screen library (a set of functions for controlling a terminal display) was part of libSystem.dylib . In Mac OS X 10.2 and 10.3, the curses library ( /usr/lib/libncurses.5.dylib ) is used in place of curses . You may still encounter source code releases that look for curses in libSystem.dylib , which will result in linking errors. You can work around this problem by adding - lcurses to the linker arguments. This is portable to earlier versions of Mac OS X as well, since /usr/lib/libcurses.dylib is a symlink to libncurses in 10.3 and 10.2, and to libSystem in earlier versions.

Interestingly enough, there is no symbolic link for libutil , whose functionality is also provided by libSystem . ( libutil is a library that provides functions related to login, logout, terminal assignment, and logging.) So, if a link fails because of - lutil , try taking it out to see if that solves the problem.

Mac OS X Panther for Unix Geeks
Mac OS X Panther for Unix Geeks
ISBN: 0596006071
EAN: 2147483647
Year: 2003
Pages: 212

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