intro —
introduction to the C libraries
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[ flags ]
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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).
- 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 (
-ltls)
- 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
bcrypt_pbkdf(3),
check_expire(3),
fmt_scaled(3),
fparseln(3),
getmaxpartitions(3),
getrawpartition(3),
imsg_init(3),
isduid(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).
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),
gprof(1),
ld(1),
ld.so(1),
nm(1),
ranlib(1),
mk.conf(5)
An
intro manual appeared in
Version 7 AT&T UNIX.
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