man/man3/intro.3

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.Dd November 27, 2024
.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
This section provides 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):
.Bl -tag -width "libbluetooth"
.It Em libbluetooth
.Pq Fl l Ns Ar bluetooth
The bluetooth library.
See
.Xr bluetooth 3 .
.It Em libc
.Pq Fl l Ns Ar c
Standard C library functions.
When using the C compiler
.Xr cc 1 ,
it is not necessary
to supply the loader flag
.Fl l Ns Ar c
for these functions.
There are several `libraries' or groups of functions included inside of
.Em libc :
.Bl -tag -width "XXXXXX"
.It standard I/O routines
see
.Xr stdio 3
.It database routines
see
.Xr db 3
.It bit operators
see
.Xr bitstring 3
.It string operators
see
.Xr string 3
.It character tests and character operators
.It storage allocation
see
.Xr mpool 3
.It regular-expressions
see
.Xr regex 3
.It remote procedure calls (RPC)
see
.Xr rpc 3
.It time functions
see
.Xr time 3
.It signal handling
see
.Xr signal 3
.El
.It Em libcalendar
.Pq Fl l Ns Ar calendar
The calendar arithmetic library.
See
.Xr calendar 3 .
.It Em libcam
.Pq Fl l Ns Ar cam
The common access method user library.
See
.Xr cam 3 .
.It Em libcrypt
.Pq Fl l Ns Ar crypt
The crypt library.
See
.Xr crypt 3 .
.It Em libcurses
.Pq Fl l Ns Ar curses Fl l Ns Ar termcap
Terminal independent screen management routines
for two dimensional non-bitmap display terminals.
See
.Xr ncurses 3 .
.It Em libcuse
.Pq Fl l Ns Ar cuse
The userland character device library.
See
.Xr cuse 3 .
.It Em libcompat
.Pq Fl l Ns Ar compat
Functions which are obsolete but are available for compatibility with
.Bx 4.3 .
In particular,
a number of system call interfaces provided in previous releases of
.Bx
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.
.It Em libdevinfo
.Pq Fl l Ns Ar devinfo
The Device and Resource Information Utility library.
See
.Xr devinfo 3 .
.It Em libdevstat
.Pq Fl l Ns Ar devstat
The Device Statistics library.
See
.Xr devstat 3 .
.It Em libdwarf
.Pq Fl l Ns Ar dwarf
The DWARF access library.
See
.Xr dwarf 3 .
.It Em libelf
.Pq Fl l Ns Ar elf
The ELF access library.
See
.Xr elf 3 .
.It Em libfetch
.Pq Fl l Ns Ar fetch
The file transfer library.
See
.Xr fetch 3 .
.It Em libfigpar
.Pq Fl l Ns Ar figpar
The configuration file parsing library.
See
.Xr figpar 3 .
.It Em libgpio
.Pq Fl l Ns Ar gpio
The general-purpose input output library (GPIO).
See
.Xr gpio 3 .
.It Em libgssapi
.Pq Fl l Ns Ar gssapi
The generic security service application programming
interface.
See
.Xr gssapi 3 .
.It Em libjail
.Pq Fl l Ns Ar jail
The jail library.
See
.Xr jail 3 .
.It Em libkvm
.Pq Fl l Ns Ar kvm
Functions used to access kernel memory are in this library.
They can be used
against both a running system and a crash dump.
See
.Xr kvm 3 .
.It Em libl
.Pq Fl l Ns Ar l
The library for
.Xr lex 1 .
.It Em libm
.Pq Fl l Ns Ar m
The math library.
See
.Xr math 3 .
.It Em libmd
.Pq Fl l Ns Ar md
The message digest library.
See
.Xr md4 3 ,
.Xr md5 3 ,
.Xr sha 3 ,
.Xr sha256 3 ,
.Xr sha512 3 ,
.Xr ripemd 3 ,
.Xr skein 3 .
.It Em libmp
.Pq Fl l Ns Ar mp
.It Em libpam
.Pq Fl l Ns Ar pam
The pluggable authentication module library.
See
.Xr pam 3 .
.It Em libpcap
.Pq Fl l Ns Ar pcap
The packet capture library.
See
.Xr pcap 3 .
.It Em libpmc
.Pq Fl l Ns Ar pmc
The performance counters library.
See
.Xr pmc 3 .
.It Em libpthread
.Pq Fl l Ns Ar pthread
The POSIX threads library.
See
.Xr pthread 3 .
.It Em libstdthreads
.Pq Fl l Ns Ar stdthreads
The ISO C11 standard
.In threads.h
library.
See
.Xr thrd_create 3 .
.It Em libsysdecode
.Pq Fl l Ns Ar sysdecode
The system argument decoding library.
See
.Xr sysdecode 3 .
.It Em libtermcap
.Pq Fl l Ns Ar termcap
The terminal independent operation library package.
See
.Xr termcap 3 .
.It Em libusb
.Pq Fl l Ns Ar usb
The USB access library.
See
.Xr usb 3 .
.It Em libvgl
.Pq Fl l Ns Ar vgl
The video graphics library.
See
.Xr vgl 3 .
.It Em liby
.Pq Fl l Ns Ar y
The library for
.Xr yacc 1 .
.It Em libz
.Pq Fl l Ns Ar z
The general-purpose data compression library.
See
.Xr zlib 3 .
.El
.Sh FILES
.Bl -tag -width /usr/lib/libm_p.a -compact
.It Pa /usr/lib/libc.a
the C library
.It Pa /usr/lib/libm.a
the math library
.El
.Sh LIBRARY TYPES
The system libraries are located in
.Pa /lib
and
.Pa /usr/lib .
A library has the following naming convention:
.Bd -unfilled -offset indent
libc.so.7
.Ed
.Pp
Libraries with an
.Sq .a
suffix are static.
When a program is linked against a static library, all necessary library code
will be included in the binary.
This means the binary can be run even when the libraries are unavailable.
However, it can be inefficient with both disk space and memory usage
during execution.
The C compiler,
.Xr cc 1 ,
can be instructed to link statically by specifying the
.Fl static
flag.
.Pp
Libraries with a
.Sq .so.X
suffix are dynamic libraries.
When code is linked dynamically, the library code that the application needs
is not included in 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 into the
process virtual address space.
.Xr rtld 1
loads the shared libraries when the program is executed.
.Pp
.Sq X
represents the library version number of the library.
In the example above, a binary linked with
.Pa libc.so.8
would not be usable on a system where only
.Pa libc.so.7
is available.
.Pp
The advantages of dynamic libraries are that multiple instances of the same
library can share address space, and the physical size of the binary is
smaller.
A namespace per shared library is available via hidden visibility,
allowing multiple compilation units in a library to share things without
making them available to other libraries.
It is possible to load libraries dynamically via
.Xr dlopen 3 .
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.
Calls across shared libraries are also slightly slower and cannot be
inlined, not even with link time optimization.
The C compiler,
.Xr cc 1 ,
can be instructed to link dynamically by specifying the
.Fl shared
flag.
.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.
The C compiler,
.Xr cc 1 ,
can be instructed to generate PIC code by specifying the
.Fl fPIC
flag.
.Pp
Static 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.
.Sh SEE ALSO
.Xr ar 1 ,
.Xr cc 1 ,
.Xr ld 1 ,
.Xr nm 1 ,
.Xr intro 2 ,
.Xr math 3 ,
.Xr stdio 3 ,
.Xr make.conf 5 ,
.Xr src.conf 5
.Sh HISTORY
An
.Nm
manual appeared in
.At v7 .