INTRO(3) Introduction to Library Functions INTRO(3)


NAME


Intro, intro - introduction to functions and libraries

DESCRIPTION


This section describes functions found in various Solaris libraries,
other than those functions described in Section 2 of this manual that
directly invoke UNIX system primitives. Function declarations can be
obtained from the #include files indicated on each page. Pages are
grouped by library and are identified by the library name (or an
abbreviation of the library name) after the section number. Collections
of related libraries are grouped into volumes as described below. The
first volume contains pages describing the contents of each shared
library and each header used by the functions, macros, and external
variables described in the remaining volumes.

Library Interfaces and Headers


This volume describes the contents of each shared library and each header
used by functions, macros, and external variables described in the
remaining volumes.

(3LIB)

The libraries described in this section are implemented as shared
objects.

Descriptions of shared objects can include a definition of the global
symbols that define the shared objects' public interface, for example
SUNW_1.1. Other interfaces can exist within the shared object, for
example SUNWprivate.1.1. The public interface provides a stable,
committed set of symbols for application development. The private
interfaces are for internal use only, and could change at any time.


(3HEAD)

The headers described in this section are used by functions, macros,
and external variables. Headers contain function prototypes,
definitions of symbolic constants, common structures, preprocessor
macros, and defined types. Each function described in the remaining
five volumes specifies the headers that an application must include
in order to use that function. In most cases only one header is
required. These headers are present on an application development
system; they do have to be present on the target execution system.


Basic Library Functions


The functions described in this volume are the core C library functions
that are basic to application development.

(3C)

These functions, together with those of Section 2, constitute the
standard C library, libc, which is automatically linked by the C
compilation system. The standard C library is implemented as a
shared object, libc.so. See libc(3LIB) and the "C Compilation System"
chapter of the ANSI C Programmer's Guide for a discussion. Some
functions behave differently in standard-conforming environments.
This behavior is noted on the individual manual pages. See
standards(5).

The libpthread and libthread libraries are filter libraries on libc
that are used for building multithreaded applications: libpthread
implements the POSIX (see standards(5)) threads interface, whereas
libthread implements the Solaris threads interface. See
MULTITHREADED APPLICATIONS, below.


(3C_DB)

These functions constitute the threads debugging library, libc_db.
This library is implemented as a shared object, libc_db.so, but is
not automatically linked by the C compilation system. Specify -lc_db
on the cc command line to link with this library. See libc_db(3LIB).


(3MALLOC)

These functions constitute the various memory allocation libraries:
libmalloc, libbsdmalloc, libmapmalloc, libmtmalloc, and libumem. Each
of these libraries is implemented as a shared object (libmalloc.so,
libbsdmalloc.so, libmapmalloc.so, libmtmalloc.so, and libumem.so).
These libraries are not automatically linked by the C compilation
system. Specify -lmalloc, -lbsdmalloc, -lmapmalloc, -lmtmalloc, and
-lumem to link with, respectively, libmalloc, libbsdmalloc,
libmapmalloc, libmtmalloc, and libumem. See libmalloc(3LIB),
libbsdmalloc(3LIB), libmapmalloc(3LIB), libmtmalloc(3LIB), and
libumem(3LIB).


Networking Library Functions


The functions described in this volume comprise the various networking
libraries.

(3COMMPUTIL)

These functions constitute the communication protocol parser
utilities library, libcommputil. This library is implemented as a
shared object, libcommputil.so, but it is not automatically linked by
the C compilation system. Specify -lcommputil on the cc command line
to link with this library. See libcommputil(3LIB).


(3DLPI)

These functions constitute the data link provider interface library,
libdlpi. This library is implemented as a shared object, libdlpi.so,
but it is not automatically linked by the C compilation system.
Specify -ldlpi on the cc command line to link with this library. See
libdlpi(3LIB).


(3DNS_SD)

These functions constitute the DNS service discovery library,
libdns_sd. This library is implemented as a shared object,
libdns_sd.so, but it is not automatically linked by the C compilation
system. Specify -ldns_sd on the cc command line to link with this
library. See libdns_sd(3LIB).


(3GSS)

These functions constitute the generic security services library.
This library is implemented as a shared object, libgss.so, but it is
not automatically linked by the C compilation system. Specify -lgss
on the cc command line to link with this library. See libgss(3LIB).


(3LDAP)

These functions constitute the lightweight directory access protocol
library, libldap. This library is implemented as a shared object,
libldap.so, but is not automatically linked by the C compilation
system. Specify -lldap on the cc command line to link with this
library. See ldap(3LDAP).


(3NSL)

These functions constitute the network service library, libnsl. This
library is implemented as a shared object, libnsl.so, but is not
automatically linked by the C compilation system. Specify -lnsl on
the cc command line to link with this library. See libnsl(3LIB).

Many base networking functions are also available in the X/Open
networking interfaces library, libxnet. See section (3XNET) below for
more information on the libxnet interfaces.


(3RESOLV)

These functions constitute the resolver library, libresolv. This
library is implemented as a shared object, libresolv.so, but is not
automatically linked by the C compilation system. Specify -lresolv on
the cc command line to link with this library. See libresolv(3LIB).


(3RPC)

These functions constitute the remote procedure call libraries,
librpcsvc and librpcsoc. The latter is provided for compatibility
only; new applications should not link to it. Both libraries are
implemented as shared objects, librpcsvc.so and librpcsoc.so,
respectively. Neither library is automatically linked by the C
compilation system. Specify -lrpcsvc or -lrpcsoc on the cc command
line to link with these libraries. See librpcsvc(3LIB).


(3SASL)

These functions constitute the simple authentication and security
layer library, libsasl. This library is implemented as a shared
object, libsasl.so, but it is not automatically linked by the C
compilation system. Specify -lsasl on the cc command line to link
with this library. See libsasl(3LIB).


(3SIP)

These functions constitute the session initiation protocol library,
libsip. This library is implemented as a shared object, libsip.so,
but it is not automatically linked by the C compilation system.
Specify -lsip on the cc command line to link with this library. See
libsip(3LIB).


(3SLP)

These functions constitute the service location protocol library,
libslp. This library is implemented as a shared object, libslp.so,
but it is not automatically linked by the C compilation system.
Specify -lslp on the cc command line to link with this library. See
libslp(3LIB).


(3SOCKET)

These functions constitute the sockets library, libsocket. This
library is implemented as a shared object, libsocket.so, but is not
automatically linked by the C compilation system. Specify -lsocket on
the cc command line to link with this library. See libsocket(3LIB).


(3XNET)

These functions constitute X/Open networking interfaces which comply
with the X/Open CAE Specification, Networking Services, Issue 4
(September, 1994). This library is implemented as a shared object,
libxnet.so, but is not automatically linked by the C compilation
system. Specify -lxnet on the cc command line to link with this
library. See libxnet(3LIB) and standards(5) for compilation
information.


Under all circumstances, the use of the Sockets API is recommended over
the XTI and TLI APIs. If portability to other XPGV4v2 (see standards(5))
systems is a requirement, the application must use the libxnet
interfaces. If portability is not required, the sockets interfaces in
libsocket and libnsl are recommended over those in libxnet. Between the
XTI and TLI APIs, the XTI interfaces (available with libxnet) are
recommended over the TLI interfaces (available with libnsl).

Curses Library Functions


The functions described in this volume comprise the libraries that
provide graphics and character screen updating capabilities.

(3CURSES)

The functions constitute the following libraries:

libcurses

These functions constitute the curses library, libcurses. This
library is implemented as a shared object, libcurses.so, but is
not automatically linked by the C compilation system. Specify
-lcurses on the cc command line to link with this library. See
libcurses(3LIB).


libform

These functions constitute the forms library, libform. This
library is implemented as a shared object, libform.so, but is not
automatically linked by the C compilation system. Specify -lform
on the cc command line to link with this library. See
libform(3LIB).


libmenu

These functions constitute the menus library, libmenu. This
library is implemented as a shared object, libmenu.so, but is not
automatically linked by the C compilation system. Specify -lmenu
on the cc command line to link with this library. See
libmenu(3LIB).


libpanel

These functions constitute the panels library, libpanel. This
library is implemented as a shared object, libpanel.so, but is
not automatically linked by the C compilation system. Specify
-lpanel on the cc command line to link with this library. See
libpanel(3LIB).


(3XCURSES)

These functions constitute the X/Open curses library, located in
/usr/xpg4/lib/libcurses.so. This library provides a set of
internationalized functions and macros for creating and modifying
input and output to a terminal screen. Included in this library are
functions for creating windows, highlighting text, writing to the
screen, reading from user input, and moving the cursor. X/Open Curses
is designed to optimize screen update activities. The X/Open Curses
library conforms fully with Issue 4 of the X/Open Extended Curses
specification. See libcurses(3XCURSES).


Extended Library Functions


The functions described in this volume comprise the following specialized
libraries:

(3BSM)

These functions constitute the auditing library, libbsm. This library
is implemented as a shared object, libbsm.so, but is not
automatically linked by the C compilation system. Specify -lbsm on
the cc command line to link with this library. See libbsm(3LIB).


(3CFGADM)

These functions constitute the configuration administration library,
libcfgadm. This library is implemented as a shared object,
libcfgadm.so, but is not automatically linked by the C compilation
system. Specify -lcfgadm on the cc command line to link with this
library. See libcfgadm(3LIB).


(3CONTRACT)

These functions constitute the contract management library,
libcontract. This library is implemented as a shared object,
libcontract.so, but is not automatically linked by the C compilation
system. Specify -lcontract on the cc command line to link with this
library. See libcontract(3LIB).


(3CPC)

These functions constitute the CPU performance counter library,
libcpc, and the process context library, libpctx. These libraries are
implemented as shared objects, libcpc.so and libpctx.so,
respectively, but are not automatically linked by the C compilation
system. Specify -lcpc or -lpctx on the cc command line to link with
these libraries. See libcpc(3LIB) and libpctx(3LIB).


(3DAT)

These functions constitute the direct access transport library,
libdat. This library is implemented as a shared object, libdat.so,
but is not automatically linked by the C compilation system. Specify
-ldat on the cc command line to link with this library. See
libdat(3LIB).


(3DEVID)

These functions constitute the device ID library, libdevid. This
library is implemented as a shared object, libdevid.so, but is not
automatically linked by the C compilation system. Specify -ldevid on
the cc command line to link with this library. See libdevid(3LIB).


(3DEVINFO)

These functions constitute the device information library,
libdevinfo. This library is implemented as a shared object,
libdevinfo.so, but is not automatically linked by the C compilation
system. Specify -ldevinfo on the cc command line to link with this
library. See libdevinfo(3LIB).


(3ELF)

These functions constitute the ELF access library, libelf,
(Extensible Linking Format). This library provides the interface for
the creation and analyses of "elf" files; executables, objects, and
shared objects. libelf is implemented as a shared object, libelf.so,
but is not automatically linked by the C compilation system. Specify
-lelf on the cc command line to link with this library. See
libelf(3LIB).


(3EXACCT)

These functions constitute the extended accounting access library,
libexacct, and the project database access library, libproject.
These libraries are implemented as shared objects, libexacct.so and
libproject.so, respectively, but are not automatically linked by the
C compilation system. Specify -lexacct or -lproject on the cc command
line to link with these libraries. See libexacct(3LIB) and
libproject(3LIB).


(3FCOE)

These functions constitute the Fibre Channel over Ethernet port
management library. This library is implemented as a shared object,
libfcoe.so, but is not automatically linked by the C compilation
system. Specify -lfcoe on the cc command line to link with this
library. See libfcoe(3LIB).


(3FSTYP)

These functions constitute the file system type identification
library. This library is implemented as a shared object, libfstyp.so,
but is not automatically linked by the C compilation system. Specify
-lfstyp on the cc command line to link with this library. See
libfstyp(3LIB).


(3GEN)

These functions constitute the string pattern-matching and pathname
manipulation library, libgen. This library is implemented as a shared
object, libgen.so, but is not automatically linked by the C
compilation system. Specify -lgen on the cc command line to link with
this library. See libgen(3LIB).


(3HBAAPI)

These functions constitute the common fibre channel HBA information
library, libhbaapi. This library is implemented as a shared object,
libhbaapi.so, but is not automatically linked by the C compilation
system. Specify -lhbaapi on the cc command line to link with this
library. See libhbaapi(3LIB).


(3ISCSIT)

These functions constitute the iSCSI Management library, libiscsit.
This library is implemented as a shared object, libiscsit.so, but is
not automatically linked by the C compilation system. Specify
-liscsit on the cc command line to link with this library. See
libiscsit(3LIB).


(3KSTAT)

These functions constitute the kernel statistics library, which is
implemented as a shared object, libkstat.so, but is not automatically
linked by the C compilation system. Specify -lkstat on the cc command
line to link with this library. See libkstat(3LIB).


(3KVM)

These functions allow access to the kernel's virtual memory library,
which is implemented as a shared object, libkvm.so, but is not
automatically linked by the C compilation system. Specify -lkvm on
the cc command line to link with this library. See libkvm(3LIB).


(3LGRP)

These functions constitute the locality group library, which is
implemented as a shared object, liblgrp.so, but is not automatically
linked by the C compilation system. Specify -llgrp on the cc command
line to link with this library. See liblgrp(3LIB).


(3M)

These functions constitute the mathematical library, libm. This
library is implemented as a shared object, libm.so, but is not
automatically linked by the C compilation system. Specify -lm on the
cc command line to link with this library. See libm(3LIB).


(3MAIL)

These functions constitute the user mailbox management library,
libmail. This library is implemented as a shared object, libmail.so,
but is not automatically linked by the C compilation system. Specify
-lmail on the cc command line to link with this library. See
libmail(3LIB).


(3MP)

These functions constitute the integer mathematical library, libmp.
This library is implemented as a shared object, libmp.so, but is not
automatically linked by the C compilation system. Specify -lmp on the
cc command line to link with this library. See libmp(3LIB).


(3MPAPI)

These functions constitute the Common Mulitipath Management library,
libMPAPI. This library is implemented as a shared object,
libMPAPI.so, but is not automatically linked by the C compilation
system. Specify -lMPAPI on the cc command line to link with this
library. See libMPAPI(3LIB).


(3MVEC)

These functions constitute the vector mathematical library, libmvec.
This library is implemented as a shared object, libmvec.so, but is
not automatically linked by the C compilation system. Specify -lmvec
on the cc command line to link with this library. See libmvec(3LIB).


(3NVPAIR)

These functions constitute the name-value pair library, libnvpair.
This library is implemented as a shared object, libnvpair.so, but is
not automatically linked by the C compilation system. Specify
-lnvpair on the cc command line to link with this library. See
libnvpair(3LIB).


(3PAM)

These functions constitute the pluggable authentication module
library, libpam. This library is implemented as a shared object,
libpam.so, but is not automatically linked by the C compilation
system. Specify -lpam on the cc command line to link with this
library. See libpam(3LIB).


(3PAPI)

These functions constitute the Free Standards Group Open Printing API
(PAPI) library, libpapi. This library is implemented as a shared
object, libpapi.so, but is not automatically linked by the C
compilation system. Specify -lpapi on the cc command line to link
with this library. See libpapi(3LIB).


(3PICL)

These functions constitute the PICL library, libpicl. This library is
implemented as a shared object, libpicl.so, but is not automatically
linked by the C compilation system. Specify -lpicl on the cc command
line to link with this library. See libpicl(3LIB) and libpicl(3PICL).


(3PICLTREE)

These functions constitute the PICL plug-in library, libpicltree.
This library is implemented as a shared object, libpicltree.so, but
is not automatically linked by the C compilation system. Specify
-lpicltree on the cc command line to link with this library. See
libpicltree(3LIB) and libpicltree(3PICLTREE).


(3POOL)

These functions constitute the pool configuration manipulation
library, libpool. This library is implemented as a shared object,
libpool.so, but is not automatically linked by the C compilation
system. Specify -lpool on the cc command line to link with this
library. See libpool(3LIB).


(3PROC)

These functions constitute the process manipulation library, libproc.
This library is implemented as a shared object, libproc.so, but it is
not automatically linked by the C compilation system. Specify -lproc
on the cc command line to link with this library. See libproc(3LIB).


(3PROJECT)

These functions constitute the project database access library,
libproject. This library is implemented as a shared object,
libproject.so, but is not automatically linked by the C compilation
system. Specify -lproject on the cc command line to link with this
library. See libproject(3LIB).


(3RSM)

These functions constitute the remote shared memory library, librsm.
This library is implemented as a shared object, librsm.so, but is not
automatically linked by the C compilation system. Specify -lrsm on
the cc command line to link with this library. See librsm(3LIB).


(3SCF)

These functions constitute the object-caching memory allocation
library, libscf. This library is implemented as a shared object,
libscf.so, but is not automatically linked by the C compilation
system. Specify -lscf on the cc command line to link with this
library. See libscf(3LIB).


(3SEC)

These functions constitute the file access control library, libsec.
This library is implemented as a shared object, libsec.so, but is not
automatically linked by the C compilation system. Specify -lsec on
the cc command line to link with this library. See libsec(3LIB).


(3SECDB)

These functions constitute the security attributes database library,
libsecdb. This library is implemented as a shared object,
libsecdb.so, but is not automatically linked by the C compilation
system. Specify -lsecdb on the cc command line to link with this
library. See libsecdb(3LIB).


(3STMF)

These functions constitute the SCSI Target Mode Framework library,
libstmf. This library is implemented as a shared object, libstmf.so,
but is not automatically linked by the C compilation system. Specify
-lstmf on the cc command line to link with this library. See
libstmf(3LIB).


(3SYSEVENT)

These functions constitute the system event library, libsysevent.
This library is implemented as a shared object, libsysevent.so, but
is not automatically linked by the C compilation system. Specify
-lsysevent on the cc command line to link with this library. See
libsysevent(3LIB).


(3TECLA)

These functions constitute the interactive command-line input
library, libtecla. This library is implemented as a shared object,
libtecla.so, but is not automatically linked by the C compilation
system. Specify -ltecla on the cc command line to link with this
library. See libtecla(3LIB).


(3TNF)

These functions constitute the TNF libraries, libtnf, libtnfctl, and
libtnfprobe. These libraries are implemented as shared objects,
libtnf.so, libtnfctl.so, and libtnfprobe.so, respectively, but are
not automatically linked by the C compilation system. Specify -ltnf,
-ltnfctl, or -ltnfprobe on the cc command line to link with these
libraries. See libtnfctl(3TNF) and libtnfctl(3LIB).


(3TSOL)

These functions constitute the Trusted Extensions library, libtsol,
and the Trusted Extensions network library, libtsnet. These libraries
are implemented as shared objects, libtsol.so and libtsnet.so, but
are not automatically linked by the C compilation system. Specify
-ltsol or -ltsnet on the cc command line to link with these
libraries. See libtsol(3LIB) and libtsnet(3LIB).


(3UUID)

These functions constitute the universally unique identifier library,
libuuid. This library is implemented as a shared object, libuuid.so,
but is not automatically linked by the C compilation system. Specify
-luuid on the cc command line to link with this library. See
libuuid(3LIB).


(3VOLMGT)

These functions constitute the volume management library, libvolmgt.
This library is implemented as a shared object, libvolmgt.so, but is
not automatically linked by the C compilation system. Specify
-lvolmgt on the cc command line to link with this library. See
libvolmgt(3LIB).


DEFINITIONS


A character is any bit pattern able to fit into a byte on the machine. In
some international languages, however, a "character" might require more
than one byte, and is represented in multi-bytes.


The null character is a character with value 0, conventionally
represented in the C language as \0. A character array is a sequence of
characters. A null-terminated character array (a string) is a sequence
of characters, the last of which is the null character. The null string
is a character array containing only the terminating null character. A
null pointer is the value that is obtained by casting 0 into a pointer. C
guarantees that this value will not match that of any legitimate pointer,
so many functions that return pointers return NULL to indicate an error.
The macro NULL is defined in <stdio.h>. Types of the form size_t are
defined in the appropriate headers.

MULTITHREADED APPLICATIONS


Both POSIX threads and Solaris threads can be used within the same
application. Their implementations are completely compatible with each
other; however, only POSIX threads guarantee portability to other POSIX-
conforming environments.


The libpthread(3LIB) and libthread(3LIB) libraries are implemented as
filters on libc(3LIB).


When compiling a multithreaded application, the -mt option must be
specified on the command line.


There is no need for a multithreaded application to link with -lthread.
An application must link with -lpthread only when POSIX semantics for
fork(2) are desired. When an application is linked with -lpthread, a call
to fork() assumes the behavior fork1(2) rather than the default behavior
that forks all threads.


When compiling a POSIX-conforming application, either the _POSIX_C_SOURCE
or _POSIX_PTHREAD_SEMANTICS option must be specified on the command line.
For POSIX.1c-conforming applications, define the _POSIX_C_SOURCE flag to
be >= 199506L:

cc -mt [ flag... ] file... -D_POSIX_C_SOURCE=199506L -lpthread


For POSIX behavior with the Solaris fork() and fork1() distinction,
compile as follows:

cc -mt [ flag... ] file... -D_POSIX_PTHREAD_SEMANTICS


For Solaris threads behavior, compile as follows:

cc -mt [ flag... ] file...


Unsafe interfaces should be called only from the main thread to ensure
the application's safety.


MT-Safe interfaces are denoted in the ATTRIBUTES section of the functions
and libraries manual pages (see attributes(5)). If a manual page does not
state explicitly that an interface is MT-Safe, the user should assume
that the interface is unsafe.

REALTIME APPLICATIONS


The environment variable LD_BIND_NOW must be set to a non-null value to
enable early binding. Refer to the "When Relocations are Processed"
chapter in Linker and Libraries Guide for additional information.

FILES


INCDIR
usually /usr/include


LIBDIR
usually either /lib or /usr/lib (32-bit) or either /lib/64
or /usr/lib/64 (64-bit)


LIBDIR/*.so
shared libraries


ACKNOWLEDGMENTS


Sun Microsystems, Inc. gratefully acknowledges The Open Group for
permission to reproduce portions of its copyrighted documentation.
Original documentation from The Open Group can be obtained online at
http://www.opengroup.org/bookstore/.


The Institute of Electrical and Electronics Engineers and The Open Group,
have given us permission to reprint portions of their documentation.


In the following statement, the phrase ``this text'' refers to portions
of the system documentation.


Portions of this text are reprinted and reproduced in electronic form in
the SunOS Reference Manual, from IEEE Std 1003.1, 2004 Edition, Standard
for Information Technology -- Portable Operating System Interface
(POSIX), The Open Group Base Specifications Issue 6, Copyright (C)
2001-2004 by the Institute of Electrical and Electronics Engineers, Inc
and The Open Group. In the event of any discrepancy between these
versions and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at
http://www.opengroup.org/unix/online.html.


This notice shall appear on any product containing this material.

SEE ALSO


ar(1), ld(1), fork(2), stdio(3C), attributes(5), standards(5)


Linker and Libraries Guide


Performance Profiling Tools


ANSI C Programmer's Guide

DIAGNOSTICS


For functions that return floating-point values, error handling varies
according to compilation mode. Under the -Xt (default) option to cc,
these functions return the conventional values 0, +-HUGE, or NaN when the
function is undefined for the given arguments or when the value is not
representable. In the -Xa and -Xc compilation modes, +-HUGE_VAL is
returned instead of +-HUGE. (HUGE_VAL and HUGE are defined in math.h to
be infinity and the largest-magnitude single-precision number,
respectively.)

NOTES


None of the functions, external variables, or macros should be redefined
in the user's programs. Any other name can be redefined without affecting
the behavior of other library functions, but such redefinition might
conflict with a declaration in an included header.


The headers in INCDIR provide function prototypes (function declarations
including the types of arguments) for most of the functions listed in
this manual. Function prototypes allow the compiler to check for correct
usage of these functions in the user's program. The lint program checker
can also be used and will report discrepancies even if the headers are
not included with #include statements. Definitions for Sections 2 and 3C
are checked automatically. Other definitions can be included by using the
-l option to lint. (For example, -lm includes definitions for libm.) Use
of lint is highly recommended. See the lint chapter in Performance
Profiling Tools


Users should carefully note the difference between STREAMS and stream.
STREAMS is a set of kernel mechanisms that support the development of
network services and data communication drivers. It is composed of
utility routines, kernel facilities, and a set of data structures. A
stream is a file with its associated buffering. It is declared to be a
pointer to a type FILE defined in <stdio.h>.


In detailed definitions of components, it is sometimes necessary to refer
to symbolic names that are implementation-specific, but which are not
necessarily expected to be accessible to an application program. Many of
these symbolic names describe boundary conditions and system limits.


In this section, for readability, these implementation-specific values
are given symbolic names. These names always appear enclosed in curly
brackets to distinguish them from symbolic names of other implementation-
specific constants that are accessible to application programs by
headers. These names are not necessarily accessible to an application
program through a header, although they can be defined in the
documentation for a particular system.


In general, a portable application program should not refer to these
symbolic names in its code. For example, an application program would not
be expected to test the length of an argument list given to a routine to
determine if it was greater than {ARG_MAX}.


August 3, 2017 INTRO(3)