INTRO(3) FreeBSD Library Functions Manual INTRO(3)
NAME
intro - introduction to the C libraries
SYNOPSIS
cc [flags] file ... [-llibrary]
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, 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):
libbluetooth (-lbluetooth) The bluetooth library. See bluetooth(3).
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:
standard I/O routines
see stdio(3)
database routines
see db(3)
bit string operators
see bitstring(3)
bit and byte utilities
see stdbit(3)
string operators
see string(3) and bstring(3)
character tests and character operators
see ctype(3)
storage allocation
see mpool(3)
regular-expressions
see regex(3)
remote procedure calls (RPC)
see rpc(3)
time functions
see time(3)
signal handling
see signal(3)
libcalendar (-lcalendar) The calendar arithmetic library. See
calendar(3).
libcam (-lcam) The common access method user library. See cam(3).
libcrypt (-lcrypt) The crypt library. See crypt(3).
libcurses (-lcurses -ltermcap) Terminal independent screen management
routines for two dimensional non-bitmap display terminals.
See ncurses(3).
libcuse (-lcuse) The userland character device library. See
cuse(3).
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.
libdevinfo (-ldevinfo) The Device and Resource Information Utility
library. See devinfo(3).
libdevstat (-ldevstat) The Device Statistics library. See devstat(3).
libdwarf (-ldwarf) The DWARF access library. See dwarf(3).
libelf (-lelf) The ELF access library. See elf(3).
libfetch (-lfetch) The file transfer library. See fetch(3).
libfigpar (-lfigpar) The configuration file parsing library. See
figpar(3).
libgpio (-lgpio) The general-purpose input output library (GPIO).
See gpio(3).
libgssapi (-lgssapi) The generic security service application
programming interface. See gssapi(3).
libjail (-ljail) The jail library. See jail(3).
libkvm (-lkvm) Functions used to access kernel memory are in this
library. They can be used against both a running system
and a crash dump. See kvm(3).
libl (-ll) The library for lex(1).
libm (-lm) The math library. See math(3).
libmd (-lmd) The message digest library. See md4(3), md5(3),
sha(3), sha256(3), sha512(3), ripemd(3), skein(3).
libmp (-lmp)
libpam (-lpam) The pluggable authentication module library. See
pam(3).
libpcap (-lpcap) The packet capture library. See pcap(3).
libpmc (-lpmc) The performance counters library. See pmc(3).
libpthread (-lpthread) The POSIX threads library. See pthread(3).
libstdthreads
(-lstdthreads) The ISO C11 standard <threads.h> library.
See thrd_create(3).
libsysdecode (-lsysdecode) The system argument decoding library. See
sysdecode(3).
libtermcap (-ltermcap) The terminal independent operation library
package. See termcap(3).
libusb (-lusb) The USB access library. See usb(3).
libvgl (-lvgl) The video graphics library. See vgl(3).
liby (-ly) The library for yacc(1).
libz (-lz) The general-purpose data compression library. See
zlib(3).
FILES
/usr/lib/libc.a the C library
/usr/lib/libm.a the math library
LIBRARY TYPES
The system libraries are located in /lib and /usr/lib. A library has the
following naming convention:
libc.so.7
Libraries with an `.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, cc(1), can be instructed
to link statically by specifying the -static flag.
Libraries with a `.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 ld.so(1) reads these data structures and
loads them into the process virtual address space. rtld(1) loads the
shared libraries when the program is executed.
`X' represents the library version number of the library. In the example
above, a binary linked with libc.so.8 would not be usable on a system
where only libc.so.7 is available.
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 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, cc(1), can be instructed to
link dynamically by specifying the -shared flag.
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. The C compiler, cc(1), can be
instructed to generate PIC code by specifying the -fPIC flag.
Static 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.
SEE ALSO
ar(1), cc(1), ld(1), nm(1), intro(2), math(3), stdio(3), make.conf(5),
src.conf(5)
HISTORY
An intro manual appeared in Version 7 AT&T UNIX.
FreeBSD 15.1-STABLE-HBSD November 10, 2025 INTRO(3)