man : intro(3)
INTRO(3) OpenBSD Programmer's Manual INTRO(3)
intro - introduction to the C libraries
cc [flags] file ... [-llibrary]
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):
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.
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.
The OpenSSL crypto library. Implements a range of cryptographic
algorithms, providing such functionality as symmetric encryption,
public key cryptography, and certificate handling. See
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).
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
Provides a mechanism to execute a function when a specific event
on a file descriptor occurs or after a given time has passed.
Library routines for parsing XML documents.
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).
GCC runtime support, including long arithmetic, propolice, and
language independent exception support. Note: users do not
normally have to explicitly link with this library.
The Generic Security Service Application Program Interface
(GSS-API) provides security services to callers in a generic
fashion. See gssapi(3).
Collection of subroutines missing in other operating systems, as
well as the C++ demangler and other functions used by the GNU
Kerberos administration client library, for talking to a Kerberos
database. Clients communicate via the network.
Kerberos administration server library, for talking to a Kerberos
database. Servers talk directly to the database.
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).
Kerberos 5 libraries. The libraries libasn1, libcom_err, libhdb,
and libkafs are all hard links to libkrb5. See krb5(3).
Kernel memory interface library. Provides a uniform interface
for accessing kernel virtual memory images, including live
systems and crash dumps. See kvm(3).
The library for lex(1), a lexical analyzer generator. The libfl
library is a hard link to libl.
Mathematical functions which comprise the C math library, libm.
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).
The sendmail(8) mail filter API. See the documentation in
Library for Objective C, an object-oriented superset of ANSI C.
Use this to compile Objective C programs.
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).
Provides an emulation of the OSS (Linux) audio interface. This
is used only for porting programs. See ossaudio(3).
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-charcter functions. See panel(3).
Packet capture library. All packets on the network, even those
destined for other hosts, are accessible through this library.
Support routines for perl(1).
IEEE Std 1003.1-2001 (``POSIX'') 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.
Command line editing interface. See readline(3).
Generated by rpcgen(1), containing stub functions for many common
Support library for the S/Key one time password (OTP)
authentication toolkit. See skey(3).
Library for audio(4) hardware and the aucat(1) audio server. See
The OpenSSL ssl library implements the Secure Sockets Layer (SSL
v2/v3) and Transport Layer Security (TLS v1) protocols. See
GCC subroutine library for C++. See c++(1). Note: users do not
normally have to explicitly link with this library.
(GCC 3.3.x systems only) C++ core language support (exceptions,
new, typeinfo). Note: users do not normally have to explicitly
link with this library.
Routines to extract data from USB Human Interface Devices (HIDs).
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),
opendev(3), opendisk(3), openpty(3), pidfile(3), pw_init(3),
pw_lock(3), readlabelfs(3) and uucplock(3).
TCP wrapper access control library. See hosts_access(3) and
The library for yacc(1), an LALR parser generator.
General purpose data compression library. The functions in this
library are documented in compress(3). The data format is
described in RFCs 1950 - 1952.
Alpha I/O and memory access functions. See inb(2).
AMD64 I/O and memory access functions. See amd64_get_ioperm(2)
ARM I/O and memory access functions. See arm_drain_writebuf(2)
i386 I/O and memory access functions. See i386_get_ioperm(2),
i386_get_ldt(2), i386_iopl(2), and i386_vm86(2).
The system libraries are located in /usr/lib. Typically, a library will
have a number of variants:
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 `3' would be linkable
against libc.so.30.1, while a binary linked with major number `31' would
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
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
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
ar(1), cc(1), gcc-local(1), gprof(1), ld.so(1), nm(1), ranlib(1),
An intro manual appeared in Version 7 AT&T UNIX.
OpenBSD 4.9 October 28, 2010 OpenBSD 4.9