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):
libbfd (-lbfd)
GNU binary file descriptor library.
Allows applications to operate on object files,
regardless of the object file format.
See
‘info bfd’.
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.
libcompat (-lcompat)
Functions which are obsolete but are available for compatibility with
4.3BSD.
In particular, a number of system call interfaces provided in previous
releases of
BSD
have been included for source code compatibility.
Use of these routines should, for the most part, be avoided.
The manual page entry for each compatibility routine
indicates the proper interface to use.
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)
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,
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).
libdes (-ldes)
Implementation of the
DES
encryption algorithm.
See
des_crypt(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)
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.
See
form(3).
libfrtbegin (-lfrtbegin)
libg2c (-lg2c)
Support routines for Fortran functions.
These two libraries were separated to allow linking Fortran code
with other languages on ELF platforms.
See
g77(1).
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.
libgssapi (-lgssapi)
The Generic Security Service Application Program Interface
(GSS-API)
provides security services to callers in a generic fashion.
See
gssapi(3).
libiberty (-liberty)
Collection of subroutines missing in other operating systems,
as well as the C++ demangler and other functions used by
the GNU toolchain.
libkadm5clnt (-lkadm5clnt)
Kerberos administration client library,
for talking to a Kerberos database.
Clients communicate via the network.
libkadm5srv (-lkadm5srv)
Kerberos administration server library,
for talking to a Kerberos database.
Servers talk directly to the database.
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).
libkrb5 (-lkrb5)
libasn1 (-lasn1)
libcom_err (-lcom_err)
libhdb (-lhdb)
libkafs (-lkafs)
Kerberos 5 libraries.
The libraries
libasn1,
libcom_err,
libhdb,
and
libkafs
are all hard links to
libkrb5.
See
krb5(3).
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 (-l\&l)
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.
See
math(3).
libmenu (-lmenu)
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.
See
menu(3).
libmilter (-lmilter)
The
sendmail(8)
mail filter API.
See the documentation in
/usr/share/doc/html/milter/.
libobjc (-lobjc)
Library for Objective C, an object-oriented superset of ANSI C.
Use this to compile Objective C programs.
libocurses (-locurses)
libotermcap (-lotermcap)
Routines to provide the user with a method of updating screens
with reasonable optimisation.
The
ocurses(3)
library is compatible with the
curses
library provided in 4.3.
libotermcap
is the 4.3-compatible
termcap
library, and is a hard link to
libocurses.
See
otermcap(3).
libopcodes (-lopcodes)
GNU opcode library.
libossaudio (-lossaudio)
Provides an emulation of the OSS
(Linux)
audio interface.
This is used only for porting programs.
See
ossaudio(3).
libpanel (-lpanel)
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.
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).
threads API and thread scheduler.
Threaded applications should use
-pthread
not
-lpthread.
See
pthreads(3).
Note: users do not normally have to explicitly link with this library.
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).
The system libraries are located in
/usr/lib.
Typically, a library will have a number of variants:
libc.a
libc.so.30.1
libc_p.a
libc_pic.a
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
‘.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
֭’
would be linkable against libc.so.30.1,
while a binary linked with major number
㣃’
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.
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
‘_pic.a’
suffix 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.
PIC code is used by shared libraries, which can make them slower.
The C compiler,
cc(1),
can be instructed to generate PIC code,
or to link with PIC libraries, 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 PIC versions of libraries and dynamic libraries can be
prevented by setting the variable
NOPIC
in
/etc/mk.conf.
The building of profiling versions of libraries and/or dynamic libraries can
be prevented by setting the variable
NOPROFILE
in
/etc/mk.conf.
See
mk.conf(5)
for more details.