intro —
introduction to the C libraries
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The manual pages in section 3 provide an overview of the C library functions,
their error returns, and other common definitions and concepts. Most of these
functions are available from the C library,
libc.
Other libraries, such as the math library,
libm,
must be indicated at compile time with the
-l
option of the compiler.
The various libraries (followed by the loader flag):
- libc (-lc)
- Standard C library functions. When using the C compiler
cc(1), it
is not necessary to supply the loader flag
-lc for these functions. There are several
“libraries” or groups of functions included inside of libc:
the standard I/O routines, database routines, bit operators, string
operators, character tests and character operators, DES encryption
routines, storage allocation, time functions, signal handling, and more.
- libc++ (-lc++)
- LLVM standard C++ library. See
clang(1).
Note: users do not normally have to explicitly link with this library.
- libc++abi (-lc++abi)
- LLVM C++ runtime library. Note: users do not normally have
to explicitly link with this library.
- libcrypto (-lcrypto)
- The OpenSSL crypto library. Implements a range of
cryptographic algorithms, providing such functionality as symmetric
encryption, public key cryptography, and certificate handling. See
crypto(3).
- libcurses (-lcurses)
-
- libncurses (-lncurses)
-
- libncursesw (-lncursesw)
-
- libtermcap (-ltermcap)
-
- libtermlib (-ltermlib)
- Terminal-independent screen management routines for
two-dimensional non-bitmap display terminals. This implementation is
“new curses” and is a replacement for
4.2BSD classic curses. The libraries
libncurses,
libncursesw,
libtermcap, and
libtermlib are all hard links to
libcurses. This is for compatibility purposes
only; new programs should link with -lcurses.
See
curses(3)
and
termcap(3).
- libedit (-ledit)
- Generic line editing and history functions, similar to
those found in
sh(1).
Functions using the libedit library must be
linked with the libcurses library, i.e.
-ledit -lcurses.
See
editline(3).
- libevent (-levent)
- Provides a mechanism to execute a function when a specific
event on a file descriptor occurs or after a given time has passed. See
event(3).
- libexpat (-lexpat)
- Library routines for parsing XML documents.
- libform (-lform)
-
- libformw (-lformw)
- Terminal-independent facilities for composing form screens
on character-cell terminals. Functions using the
libform library must be linked with the
libcurses library, i.e.
-lform -lcurses.
libformw is a hard link to
libform intended for use with
libncursesw wide-character functions. See
form(3).
- libfuse (-lfuse)
- File system in userland library. See
fuse_main(3).
- libgcc (-lgcc)
- GCC runtime support, including long arithmetic, propolice,
and language independent exception support. Note: users do not normally
have to explicitly link with this library.
- libiberty (-liberty)
- Collection of subroutines missing in other operating
systems, as well as the C++ demangler and other functions used by the GNU
toolchain.
- libkeynote (-lkeynote)
- System library for the keynote trust-management system.
Trust-management systems provide standard, general-purpose mechanisms for
specifying application security policies and credentials. Functions using
the libkeynote library must be linked with the
libm and
libcrypto libraries, i.e.
-lkeynote -lm
-lcrypto. See
keynote(3)
and
keynote(4).
- libkvm (-lkvm)
- Kernel memory interface library. Provides a uniform
interface for accessing kernel virtual memory images, including live
systems and crash dumps. See
kvm(3).
- libl (-ll)
-
- libfl (-lfl)
- The library for
lex(1),
a lexical analyzer generator. The libfl
library is a hard link to libl.
- libm (-lm)
- Mathematical functions which comprise the C math library,
libm.
- libmenu (-lmenu)
-
- libmenuw (-lmenuw)
- Terminal-independent facilities for composing menu systems
on character-cell terminals. Functions using the
libmenu library must be linked with the
libcurses library, i.e.
-lmenu -lcurses.
libmenuw is a hard link to
libmenu intended for use with
libncursesw wide-character functions. See
menu(3).
- libobjc (-lobjc)
- Library for Objective C, an object-oriented superset of
ANSI C. Use this to compile Objective C programs.
- libossaudio (-lossaudio)
- Provides an emulation of the OSS (Linux) audio interface.
This is used only for porting programs. See
ossaudio(3).
- libpanel (-lpanel)
-
- libpanelw (-lpanelw)
- Terminal-independent facilities for stacked windows on
character-cell terminals. Functions using the
libpanel library must be linked with the
libcurses library, i.e.
-lpanel
-lcurses.
libpanelw is a hard link to
libpanel intended for use with
libncursesw wide-character functions. See
panel(3).
- libpcap (-lpcap)
- Packet capture library. All packets on the network, even
those destined for other hosts, are accessible through this library. See
pcap(3).
- libperl (-lperl)
- Support routines for
perl(1).
- libpthread (-lpthread)
- IEEE Std 1003.1-2001
(“POSIX.1”) threads API. See
pthreads(3).
- libradius (-lradius)
- Support routines for the RADIUS library. See
radius_new_request_packet(3).
- libreadline (-lreadline)
- Command line editing interface. See
readline(3).
- librpcsvc (-lrpcsvc)
- Generated by
rpcgen(1),
containing stub functions for many common
rpc(3)
protocols.
- libskey (-lskey)
- Support library for the S/Key one time password (OTP)
authentication toolkit. See
skey(3).
- libsndio (-lsndio)
- Library for
audio(4)
hardware and the
aucat(1)
audio server. See
sio_open(3).
- libssl (-lssl)
- The OpenSSL ssl library implements the Secure Sockets Layer
(SSL v3) and Transport Layer Security (TLS v1) protocols. See
ssl(3).
- libstdc++ (-lstdc++)
- GNU standard C++ library. See
g++(1).
Note: users do not normally have to explicitly link with this library.
- libsupc++ (-lsupc++)
- GNU C++ runtime library. Note: users do not normally have
to explicitly link with this library.
- libtls (-tls)
- A Transport Layer Security library with a clean and easy to
use interface. See
tls_init(3).
- libusbhid (-lusbhid)
- Routines to extract data from USB Human Interface Devices
(HIDs). See
usbhid(3).
- libutil (-lutil)
- System utility functions. These are currently
check_expire(3),
fmt_scaled(3),
fparseln(3),
getmaxpartitions(3),
getrawpartition(3),
imsg_init(3),
login(3),
login_fbtab(3),
ohash_init(3),
ohash_interval(3),
opendev(3),
opendisk(3),
openpty(3),
pidfile(3),
pkcs5_pbkdf2(3),
pw_init(3),
pw_lock(3),
readlabelfs(3)
and
uucplock(3).
- liby (-ly)
- The library for
yacc(1),
an LALR parser generator.
- libz (-lz)
- General purpose data compression library. The functions in
this library are documented in
compress(3).
The data format is described in RFCs 1950 - 1952.
Platform-specific libraries:
-
-
- libalpha (-lalpha)
- Alpha I/O and memory access functions. See
inb(2).
-
-
- libamd64 (-lamd64)
- AMD64 I/O and memory access functions. See
amd64_iopl(2).
-
-
- libi386 (-li386)
- i386 I/O and memory access functions. See
i386_iopl(2)
and
i386_vm86(2).
The system libraries are located in
/usr/lib.
Typically, a library will have a number of variants:
libc.a
libc_p.a
libc.so.30.1
Libraries with an ‘.a’ suffix are static. When a program is linked
against a library, all the library code will be linked into the binary. This
means the binary can be run even when the libraries are unavailable. However,
it can be inefficient with memory usage. The C compiler,
cc(1), can be
instructed to link statically by specifying the
-static flag.
Libraries with a ‘_p.a’ suffix are profiling libraries. They
contain extra information suitable for analysing programs, such as execution
speed and call counts. This in turn can be interpreted by utilities such as
gprof(1).
The C compiler,
cc(1), can be
instructed to generate profiling code, or to link with profiling libraries, by
specifying the
-pg flag.
Libraries with a ‘.so.X.Y’ suffix are dynamic libraries. When code
is compiled dynamically, the library code that the application needs is not
linked into the binary. Instead, data structures are added containing
information about which dynamic libraries to link with. When the binary is
executed, the run-time linker
ld.so(1)
reads these data structures, and loads them at a virtual address using the
mmap(2)
system call.
‘X’ represents the major number of the library, and
‘Y’ represents the minor number. In general, a binary will be
able to use a dynamic library with a differing minor number, but the major
numbers must match. In the example above, a binary linked with minor number
‘3’ would be linkable against libc.so.30.1, while a binary
linked with major number ‘31’ would not.
The advantages of dynamic libraries are that multiple instances of the same
program can share address space, and the physical size of the binary is
smaller. The disadvantage is the added complexity that comes with loading the
libraries dynamically, and the extra time taken to load the libraries. Of
course, if the libraries are not available, the binary will be unable to
execute. The C compiler,
cc(1), can be
instructed to link dynamically by specifying the
-shared flag, although on systems that support
it, this will be the default and need not be specified.
Shared libraries, as well as static libraries on architectures which produce
position-independent executables (PIEs) by default, contain
position-independent code (PIC). Normally, compilers produce relocatable code.
Relocatable code needs to be modified at run-time, depending on where in
memory it is to be run. PIC code does not need to be modified at run-time, but
is less efficient than relocatable code. The C compiler,
cc(1), can be
instructed to generate PIC code by specifying the
-fpic or
-fPIC
flags.
With the exception of dynamic libraries, libraries are generated using the
ar(1)
utility. The libraries contain an index to the contents of the library, stored
within the library itself. The index lists each symbol defined by a member of
a library that is a relocatable object file. This speeds up linking to the
library, and allows routines in the library to call each other regardless of
their placement within the library. The index is created by
ranlib(1)
and can be viewed using
nm(1).
The building of dynamic libraries can be prevented by setting the variable
NOPIC in
/etc/mk.conf. The building of profiling versions
of libraries can be prevented by setting the variable
NOPROFILE in
/etc/mk.conf. See
mk.conf(5)
for more details.
ar(1),
cc(1),
gcc-local(1),
gprof(1),
ld(1),
ld.so(1),
nm(1),
ranlib(1),
mk.conf(5)
An
intro manual appeared in
Version 7 AT&T UNIX.