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.\"     @(#)intro.3	8.1 (Berkeley) 6/5/93
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.Dd $Mdocdate: October 26 2020 $
.Dt INTRO 3
.Os
.Sh NAME
.Nm intro
.Nd introduction to the C libraries
.Sh SYNOPSIS
.Nm cc
.Op Ar flags
.Ar
.Op Fl llibrary
.Sh DESCRIPTION
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,
.Em libc .
Other libraries, such as the math library,
.Em libm ,
must be indicated at compile time with the
.Fl l
option of the compiler.
.Pp
The various libraries (followed by the loader flag):
.Pp
.Bl -tag -width "libkvm" -compact
.It libLLVM Pq Fl lLLVM
LLVM components in a single library.
.Pp
.It libagentx Pq Fl lagentx
AgentX client library.
Used for applications to export metrics to AgentX capable snmp daemons.
See
.Xr agentx 3 .
.Pp
.It libc Pq Fl lc
Standard C library functions.
When using the C compiler
.Xr cc 1 ,
it is not necessary to supply the loader flag
.Fl lc
for these functions.
There are several
.Dq 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,
cryptographic routines,
storage allocation,
time functions,
signal handling,
and more.
.Pp
.It libc++ Pq Fl lc++
LLVM standard C++ library.
See
.Xr clang 1 .
Note: users do not normally have to explicitly link with this library.
.Pp
.It libc++abi Pq Fl lc++abi
LLVM C++ runtime library.
Note: users do not normally have to explicitly link with this library.
.Pp
.It libcbor Pq Fl lcbor
An implementation of the Concise Binary Object Representation
.Pq CBOR
encoding format defined in RFC 7049.
.Pp
.It libcrypto Pq Fl lcrypto
The OpenSSL crypto library.
Implements a range of cryptographic algorithms,
providing such functionality as symmetric encryption, public key cryptography,
and certificate handling.
See
.Xr crypto 3 .
.Pp
.It libcurses Pq Fl lcurses
.It libncurses Pq Fl lncurses
.It libncursesw Pq Fl lncursesw
.It libtermcap Pq Fl ltermcap
.It libtermlib Pq Fl ltermlib
Terminal-independent screen management routines for two-dimensional
non-bitmap display terminals.
This implementation is
.Dq new curses
and is a replacement for
.Bx 4.2
classic curses.
The libraries
.Em libncurses ,
.Em libncursesw ,
.Em libtermcap ,
and
.Em libtermlib
are all hard links to
.Em libcurses .
This is for compatibility purposes only;
new programs should link with
.Fl lcurses .
See
.Xr curses 3
and
.Xr termcap 3 .
.Pp
.It libedit Pq Fl ledit
Generic line editing and history functions, similar to those found in
.Xr sh 1 .
Functions using the
.Em libedit
library must be linked with the
.Em libcurses
library, i.e.\&
.Fl ledit lcurses .
See
.Xr editline 3 .
.Pp
.It libelf Pq Fl lelf
Library routines for manipulating ELF objects.
See
.Xr elf 3 .
.Pp
.It libevent Pq Fl 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
.Xr event 3 .
.Pp
.It libexpat Pq Fl lexpat
Library routines for parsing XML documents.
.Pp
.It libfido2 Pq Fl lfido2
Library for communication with U2F/FIDO2 devices over USB.
.Pp
.It libform Pq Fl lform
.It libformw Pq Fl lformw
Terminal-independent facilities for composing form screens on
character-cell terminals.
Functions using the
.Em libform
library must be linked with the
.Em libcurses
library, i.e.\&
.Fl lform lcurses .
.Em libformw
is a hard link to
.Em libform
intended for use with
.Em libncursesw
wide-character functions.
See
.Xr form 3 .
.Pp
.It libfuse Pq Fl lfuse
File system in userland library.
See
.Xr fuse_main 3 .
.Pp
.It libgcc Pq Fl 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.
.Pp
.It libiberty Pq Fl liberty
Collection of subroutines missing in other operating systems,
as well as the C++ demangler and other functions used by
the GNU toolchain.
.Pp
.It libkeynote Pq Fl 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
.Em libm
and
.Em libcrypto
libraries, i.e.\&
.Fl lkeynote lm lcrypto .
See
.Xr keynote 3
and
.Xr keynote 4 .
.Pp
.It libkvm Pq Fl lkvm
Kernel memory interface library.
Provides a uniform interface for accessing kernel virtual memory images,
including live systems and crash dumps.
See
.Xr kvm 3 .
.Pp
.It libl Pq Fl l\&l
.It libfl Pq Fl lfl
The library for
.Xr lex 1 ,
a lexical analyzer generator.
The
.Em libfl
library
is a hard link to
.Em libl .
.Pp
.It libm Pq Fl lm
Mathematical functions which comprise the C math library,
.Em libm .
.Pp
.It libmenu Pq Fl lmenu
.It libmenuw Pq Fl lmenuw
Terminal-independent facilities for composing menu systems on
character-cell terminals.
Functions using the
.Em libmenu
library must be linked with the
.Em libcurses
library, i.e.\&
.Fl lmenu lcurses .
.Em libmenuw
is a hard link to
.Em libmenu
intended for use with
.Em libncursesw
wide-character functions.
See
.Xr menu 3 .
.Pp
.It libossaudio Pq Fl lossaudio
Provides an emulation of the OSS
.Pq Linux
audio interface.
This is used only for porting programs.
See
.Xr ossaudio 3 .
.Pp
.It libpanel Pq Fl lpanel
.It libpanelw Pq Fl lpanelw
Terminal-independent facilities for stacked windows on
character-cell terminals.
Functions using the
.Em libpanel
library must be linked with the
.Em libcurses
library, i.e.\&
.Fl lpanel lcurses .
.Em libpanelw
is a hard link to
.Em libpanel
intended for use with
.Em libncursesw
wide-character functions.
See
.Xr panel 3 .
.Pp
.It libpcap Pq Fl lpcap
Packet capture library.
All packets on the network, even those destined for other hosts,
are accessible through this library.
See
.Xr pcap_open_live 3 .
.Pp
.It libperl Pq Fl lperl
Support routines for
.Xr perl 1 .
.Pp
.It libpthread Pq Fl lpthread
.St -p1003.1-2001
threads API.
See
.Xr pthreads 3 .
.Pp
.It libradius Pq Fl lradius
Support routines for the RADIUS library.
See
.Xr radius_new_request_packet 3 .
.Pp
.It libreadline Pq Fl lreadline
Command line editing interface.
See
.Xr readline 3 .
.Pp
.It librpcsvc Pq Fl lrpcsvc
Generated by
.Xr rpcgen 1 ,
containing stub functions for many common
.Xr rpc 3
protocols.
.Pp
.It libskey Pq Fl lskey
Support library for the S/Key one time password
.Pq OTP
authentication toolkit.
See
.Xr skey 3 .
.Pp
.It libsndio Pq Fl lsndio
Library for
.Xr audio 4
hardware and the
.Xr aucat 1
audio server.
See
.Xr sio_open 3 .
.Pp
.It libssl Pq Fl lssl
The OpenSSL ssl library implements the Secure Sockets Layer
.Pq SSL v3
and Transport Layer Security
.Pq TLS v1
protocols.
See
.Xr ssl 3 .
.Pp
.It libstdc++ Pq Fl lstdc++
GNU standard C++ library.
See
.Xr g++ 1 .
Note: users do not normally have to explicitly link with this library.
.Pp
.It libsupc++ Pq Fl lsupc++
GNU C++ runtime library.
Note: users do not normally have to explicitly link with this library.
.Pp
.It libtls Pq Fl ltls
A Transport Layer Security library with a clean and easy to use interface.
See
.Xr tls_init 3 .
.Pp
.It libusbhid Pq Fl lusbhid
Routines to extract data from USB Human Interface Devices
.Pq HIDs .
See
.Xr usbhid 3 .
.Pp
.It libutil Pq Fl lutil
System utility functions.
.Pp
.It liby Pq Fl ly
The library for
.Xr yacc 1 ,
an LALR parser generator.
.Pp
.It libz Pq Fl lz
General purpose data compression library.
The functions in this library are documented in
.Xr compress 3 .
The data format is described in RFCs 1950 \- 1952.
.El
.Pp
Platform-specific libraries:
.Bl -tag -width "libkvm"
.It libalpha Pq Fl lalpha
Alpha I/O and memory access functions.
See
.Xr inb 2 .
.It libamd64 Pq Fl lamd64
AMD64 I/O and memory access functions.
See
.Xr amd64_iopl 2 .
.It libi386 Pq Fl li386
i386 I/O and memory access functions.
See
.Xr i386_iopl 2 .
.El
.Sh LIBRARY TYPES
The system libraries are located in
.Pa /usr/lib .
Typically, a library will have a number of variants:
.Bd -unfilled -offset indent
libc.a
libc_p.a
libc.so.30.1
.Ed
.Pp
Libraries with an
.Sq .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,
.Xr cc 1 ,
can be instructed to link statically by specifying the
.Fl static
flag.
.Pp
Libraries with a
.Sq _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
.Xr gprof 1 .
The C compiler,
.Xr cc 1 ,
can be instructed to generate profiling code,
or to link with profiling libraries, by specifying the
.Fl pg
flag.
.Pp
Libraries with a
.Sq .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
.Xr ld.so 1
reads these data structures, and loads them at a virtual address using the
.Xr mmap 2
system call.
.Pp
.Sq X
represents the major number of the library, and
.Sq 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
.Sq 3
would be linkable against libc.so.30.1,
while a binary linked with major number
.Sq 31
would not.
.Pp
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,
.Xr cc 1 ,
can be instructed to link dynamically by specifying the
.Fl shared
flag, although on systems that support it, this will be the default and
need not be specified.
.Pp
Shared libraries, as well as static libraries on architectures which produce
position-independent executables
.Pq PIEs
by default, contain position-independent code
.Pq 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,
.Xr cc 1 ,
can be instructed to generate PIC code by specifying the
.Fl fpic
or
.Fl fPIC
flags.
.Pp
With the exception of dynamic libraries, libraries are generated using the
.Xr 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
.Xr ranlib 1
and can be viewed using
.Xr nm 1 .
.Pp
The building of dynamic libraries can be prevented by setting the variable
.Dv NOPIC
in
.Pa /etc/mk.conf .
The building of profiling versions of libraries can
be prevented by setting the variable
.Dv NOPROFILE
in
.Pa /etc/mk.conf .
See
.Xr mk.conf 5
for more details.
.Sh SEE ALSO
.Xr ar 1 ,
.Xr cc 1 ,
.Xr gprof 1 ,
.Xr ld 1 ,
.Xr ld.so 1 ,
.Xr nm 1 ,
.Xr ranlib 1 ,
.Xr mk.conf 5
.Sh HISTORY
An
.Nm
manual for section 3 first appeared in
.At v7 .