+++ /dev/null
-.\" This manpage is Copyright (C) 2006, Michael Kerrisk
-.\"
-.\" %%%LICENSE_START(VERBATIM)
-.\" Permission is granted to make and distribute verbatim copies of this
-.\" manual provided the copyright notice and this permission notice are
-.\" preserved on all copies.
-.\"
-.\" Permission is granted to copy and distribute modified versions of this
-.\" manual under the conditions for verbatim copying, provided that the
-.\" entire resulting derived work is distributed under the terms of a
-.\" permission notice identical to this one.
-.\"
-.\" Since the Linux kernel and libraries are constantly changing, this
-.\" manual page may be incorrect or out-of-date. The author(s) assume no
-.\" responsibility for errors or omissions, or for damages resulting from
-.\" the use of the information contained herein. The author(s) may not
-.\" have taken the same level of care in the production of this manual,
-.\" which is licensed free of charge, as they might when working
-.\" professionally.
-.\"
-.\" Formatted or processed versions of this manual, if unaccompanied by
-.\" the source, must acknowledge the copyright and authors of this work.
-.\" %%%LICENSE_END
-.\"
-.TH FEATURE_TEST_MACROS 7 2014-03-20 "Linux" "Linux Programmer's Manual"
-.SH NAME
-feature_test_macros \- feature test macros
-.SH SYNOPSIS
-.nf
-.B #include <features.h>
-.fi
-.SH DESCRIPTION
-Feature test macros allow the programmer to control the definitions that
-are exposed by system header files when a program is compiled.
-
-.B NOTE:
-In order to be effective, a feature test macro
-.IR "must be defined before including any header files" .
-This can be done either in the compilation command
-.RI ( "cc \-DMACRO=value" )
-or by defining the macro within the source code before
-including any headers.
-
-Some feature test macros are useful for creating portable applications,
-by preventing nonstandard definitions from being exposed.
-Other macros can be used to expose nonstandard definitions that
-are not exposed by default.
-The precise effects of each of the feature test macros described below
-can be ascertained by inspecting the
-.I <features.h>
-header file.
-.SS Specification of feature test macro requirements in manual pages
-When a function requires that a feature test macro is defined,
-the manual page SYNOPSIS typically includes a note of the following form
-(this example from the
-.BR acct (2)
-manual page):
-.RS 8
-.sp
-.B #include <unistd.h>
-.sp
-.BI "int acct(const char *" filename );
-.sp
-.nf
-.in -4n
-Feature Test Macro Requirements for glibc (see
-.BR feature_test_macros (7)):
-.fi
-.in
-.sp
-.BR acct ():
-_BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE\ <\ 500)
-.RE
-.PP
-The
-.B ||
-means that in order to obtain the declaration of
-.BR acct (2)
-from
-.IR <unistd.h> ,
-.I either
-of the following macro
-definitions must be made before including any header files:
-.RS
-.nf
-
-#define _BSD_SOURCE
-#define _XOPEN_SOURCE /* or any value < 500 */
-.fi
-.RE
-.PP
-Alternatively, equivalent definitions can be included in the
-compilation command:
-.RS
-.nf
-
-cc \-D_BSD_SOURCE
-cc \-D_XOPEN_SOURCE # Or any value < 500
-.fi
-.RE
-.PP
-Note that, as described below,
-.BR "some feature test macros are defined by default" ,
-so that it may not always be necessary to
-explicitly specify the feature test macro(s) shown in the
-SYNOPSIS.
-
-In a few cases, manual pages use a shorthand for expressing the
-feature test macro requirements (this example from
-.BR readahead (2)):
-.RS
-.nf
-
-.B #define _GNU_SOURCE
-.B #include <fcntl.h>
-.sp
-.BI "ssize_t readahead(int " fd ", off64_t *" offset ", size_t " count );
-.fi
-.RE
-.PP
-This format is employed in cases where only a single
-feature test macro can be used to expose the function
-declaration, and that macro is not defined by default.
-.SS Feature test macros understood by glibc
-The following paragraphs explain how feature test macros are handled
-in Linux glibc 2.\fIx\fP,
-.I x
-> 0.
-.\" The details in glibc 2.0 are simpler, but combining a
-.\" a description of them with the details in later glibc versions
-.\" would make for a complicated description.
-
-Linux glibc understands the following feature test macros:
-.TP
-.B __STRICT_ANSI__
-ISO Standard C.
-This macro is implicitly defined by
-.BR gcc (1)
-when invoked with, for example, the
-.I -std=c99
-or
-.I -ansi
-flag.
-.TP
-.B _POSIX_C_SOURCE
-Defining this macro causes header files to expose definitions as follows:
-.RS
-.IP \(bu 3
-The value 1 exposes definitions conforming to POSIX.1-1990 and
-ISO C (1990).
-.IP \(bu
-The value 2 or greater additionally exposes
-definitions for POSIX.2-1992.
-.IP \(bu
-The value 199309L or greater additionally exposes
-definitions for POSIX.1b (real-time extensions).
-.\" 199506L functionality is available only since glibc 2.1
-.IP \(bu
-The value 199506L or greater additionally exposes
-definitions for POSIX.1c (threads).
-.IP \(bu
-(Since glibc 2.3.3)
-The value 200112L or greater additionally exposes definitions corresponding
-to the POSIX.1-2001 base specification (excluding the XSI extension)
-and also causes C95 (since glibc 2.12) and
-C99 (since glibc 2.10) features to be exposed.
-.IP \(bu
-(Since glibc 2.10)
-The value 200809L or greater additionally exposes definitions corresponding
-to the POSIX.1-2008 base specification (excluding the XSI extension).
-.RE
-.TP
-.B _POSIX_SOURCE
-Defining this obsolete macro with any value is equivalent to defining
-.B _POSIX_C_SOURCE
-with the value 1.
-.TP
-.B _XOPEN_SOURCE
-Defining this macro causes header files to expose definitions as follows:
-.RS
-.IP \(bu 3
-Defining with any value exposes
-definitions conforming to POSIX.1, POSIX.2, and XPG4.
-.IP \(bu
-The value 500 or greater additionally exposes
-definitions for SUSv2 (UNIX 98).
-.IP \(bu
-(Since glibc 2.2) The value 600 or greater additionally exposes
-definitions for SUSv3 (UNIX 03; i.e., the POSIX.1-2001 base specification
-plus the XSI extension) and C99 definitions.
-.IP \(bu
-(Since glibc 2.10) The value 700 or greater additionally exposes
-definitions for SUSv4 (i.e., the POSIX.1-2008 base specification
-plus the XSI extension).
-.RE
-.IP
-If
-.B __STRICT_ANSI__
-is not defined, or
-.BR _XOPEN_SOURCE
-is defined with a value greater than or equal to 500
-.I and
-neither
-.B _POSIX_SOURCE
-not
-.B _POSIX_C_SOURCE
-is explicitly defined, then
-the following macros are implicitly defined:
-.RS
-.IP \(bu 3
-.B _POSIX_SOURCE
-is defined with the value 1.
-.IP \(bu
-.B _POSIX_C_SOURCE
-is defined, according to the value of
-.BR _XOPEN_SOURCE :
-.RS 7
-.TP
-.BR _XOPEN_SOURCE " < 500"
-.B _POSIX_C_SOURCE
-is defined with the value 2.
-.TP
-.RB "500 <= " _XOPEN_SOURCE " < 600"
-.B _POSIX_C_SOURCE
-is defined with the value 199506L.
-.TP
-.RB "600 <= " _XOPEN_SOURCE " < 700"
-.B _POSIX_C_SOURCE
-is defined with the value 200112L.
-.TP
-.RB "700 <= " _XOPEN_SOURCE " (since glibc 2.10)"
-.B _POSIX_C_SOURCE
-is defined with the value 200809L.
-.RE
-.RE
-.TP
-.B _XOPEN_SOURCE_EXTENDED
-If this macro is defined, and
-.B _XOPEN_SOURCE
-is defined, then expose definitions corresponding to the XPG4v2
-(SUSv1) UNIX extensions (UNIX 95).
-This macro is also implicitly defined if
-.B _XOPEN_SOURCE
-is defined with a value of 500 or more.
-.TP
-.BR _ISOC99_SOURCE " (since glibc 2.1.3)"
-Exposes declarations consistent with the ISO C99 standard.
-
-Earlier glibc 2.1.x versions recognized an equivalent macro named
-.B _ISOC9X_SOURCE
-(because the C99 standard had not then been finalized).
-Although the use of this macro is obsolete, glibc continues
-to recognize it for backward compatibility.
-
-Defining
-.B _ISOC99_SOURCE
-also exposes ISO C (1990) Amendment 1 ("C95") definitions.
-(The primary change in C95 was support for international character sets.)
-.TP
-.BR _ISOC11_SOURCE " (since glibc 2.16)"
-Exposes declarations consistent with the ISO C11 standard.
-Defining this macro also enables C99 and C95 features (like
-.BR _ISOC99_SOURCE ).
-.TP
-.B _LARGEFILE64_SOURCE
-Expose definitions for the alternative API specified by the
-LFS (Large File Summit) as a "transitional extension" to the
-Single UNIX Specification.
-(See
-.UR http:\:/\:/opengroup.org\:/platform\:/lfs.html
-.UE .)
-The alternative API consists of a set of new objects
-(i.e., functions and types) whose names are suffixed with "64"
-(e.g.,
-.I off64_t
-versus
-.IR off_t ,
-.BR lseek64 ()
-versus
-.BR lseek (),
-etc.).
-New programs should not employ this macro; instead
-.I _FILE_OFFSET_BITS=64
-should be employed.
-.TP
-.BR _LARGEFILE_SOURCE
-This macro was historically used to expose certain functions (specifically
-.BR fseeko (3)
-and
-.BR ftello (3))
-that address limitations of earlier APIs
-.RB ( feek (3)
-and
-.BR ftell (3))
-that use
-.IR "long int"
-for file offsets.
-This macro is implicitly defined if
-.BR _XOPEN_SOURCE
-is defined with a value greater than or equal to 500.
-New programs should not employ this macro;
-defining
-.BR _XOPEN_SOURCE
-as just described or defining
-.B _FILE_OFFSET_BITS
-with the value 64 is the preferred mechanism to achieve the same result.
-.TP
-.B _FILE_OFFSET_BITS
-Defining this macro with the value 64
-automatically converts references to 32-bit functions and data types
-related to file I/O and filesystem operations into references to
-their 64-bit counterparts.
-This is useful for performing I/O on large files (> 2 Gigabytes)
-on 32-bit systems.
-(Defining this macro permits correctly written programs to use
-large files with only a recompilation being required.)
-
-64-bit systems naturally permit file sizes greater than 2 Gigabytes,
-and on those systems this macro has no effect.
-.TP
-.BR _BSD_SOURCE " (deprecated since glibc 2.20)"
-Defining this macro with any value causes header files to expose
-BSD-derived definitions.
-
-In glibc versions up to and including 2.18,
-defining this macro also causes BSD definitions to be preferred in
-some situations where standards conflict, unless one or more of
-.BR _SVID_SOURCE ,
-.BR _POSIX_SOURCE ,
-.BR _POSIX_C_SOURCE ,
-.BR _XOPEN_SOURCE ,
-.BR _XOPEN_SOURCE_EXTENDED ,
-or
-.B _GNU_SOURCE
-is defined, in which case BSD definitions are disfavored.
-Since glibc 2.19,
-.B _BSD_SOURCE
-no longer causes BSD definitions to be preferred in case of conflicts.
-
-Since glibc 2.20, this macro is deprecated.
-.\" commit c941736c92fa3a319221f65f6755659b2a5e0a20
-.\" commit 498afc54dfee41d33ba519f496e96480badace8e
-.\" commit acd7f096d79c181866d56d4aaf3b043e741f1e2c
-It now has the same effect as defining
-.BR _DEFAULT_SOURCE ,
-but generates a compile-time warning (unless
-.BR _DEFAULT_SOURCE
-.\" commit ade40b10ff5fa59a318cf55b9d8414b758e8df78
-is also defined).
-Use
-.B _DEFAULT_SOURCE
-instead.
-To allow code that requires
-.BR _BSD_SOURCE
-in glibc 2.19 and earlier and
-.BR _DEFAULT_SOURCE
-in glibc 2.20 and later to compile without warnings, define
-.I both
-.B _BSD_SOURCE
-and
-.BR _DEFAULT_SOURCE .
-.TP
-.BR _SVID_SOURCE " (deprecated since glibc 2.20)"
-Defining this macro with any value causes header files to expose
-System V-derived definitions.
-(SVID == System V Interface Definition; see
-.BR standards (7).)
-
-Since glibc 2.20, this macro is deprecated in the same fashion as
-.BR _BSD_SOURCE .
-.TP
-.BR _DEFAULT_SOURCE " (since glibc 2.19)"
-This macro can be defined to ensure that the "default"
-definitions are provided even when the defaults would otherwise
-be disabled,
-as happens when individual macros are explicitly defined,
-or the compiler is invoked in one of its "standard" modes (e.g.,
-.IR "cc\ \-std=c99" ).
-Defining
-.B _DEFAULT_SOURCE
-without defining other individual macros
-or invoking the compiler in one of its "standard" modes has no effect.
-
-The "default" definitions comprise those required by POSIX.1-2008
-as well as various definitions derived from BSD and System V.
-On glibc 2.19 and earlier, these defaults were approximately equivalent
-to explicitly defining the following:
-
- cc \-D_BSD_SOURCE \-D_SVID_SOURCE \-D_POSIX_C_SOURCE=200809
-
-.TP
-.BR _ATFILE_SOURCE " (since glibc 2.4)"
-Defining this macro with any value causes header files to expose
-declarations of a range of functions with the suffix "at";
-see
-.BR openat (2).
-Since glibc 2.10, this macro is also implicitly defined if
-.BR _POSIX_C_SOURCE
-is defined with a value greater than or equal to 200809L.
-.TP
-.B _GNU_SOURCE
-Defining this macro (with any value) implicitly defines
-.BR _ATFILE_SOURCE ,
-.BR _LARGEFILE64_SOURCE ,
-.BR _ISOC99_SOURCE ,
-.BR _XOPEN_SOURCE_EXTENDED ,
-.BR _POSIX_SOURCE ,
-.B _POSIX_C_SOURCE
-with the value 200809L
-(200112L in glibc versions before 2.10;
-199506L in glibc versions before 2.5;
-199309L in glibc versions before 2.1)
-and
-.B _XOPEN_SOURCE
-with the value 700
-(600 in glibc versions before 2.10;
-500 in glibc versions before 2.2).
-In addition, various GNU-specific extensions are also exposed.
-
-Since glibc 2.19, defining
-.BR _GNU_SOURCE
-also has the effect of implicitly defining
-.BR _DEFAULT_SOURCE .
-In glibc versions before 2.20, defining
-.BR _GNU_SOURCE
-also had the effect of implicitly defining
-.BR _BSD_SOURCE
-and
-.BR _SVID_SOURCE .
-.TP
-.B _REENTRANT
-Defining this macro exposes definitions of certain reentrant functions.
-For multithreaded programs, use
-.I "cc\ \-pthread"
-instead.
-.TP
-.B _THREAD_SAFE
-Synonym for
-.BR _REENTRANT ,
-provided for compatibility with some other implementations.
-.TP
-.BR _FORTIFY_SOURCE " (since glibc 2.3.4)"
-.\" For more detail, see:
-.\" http://gcc.gnu.org/ml/gcc-patches/2004-09/msg02055.html
-.\" [PATCH] Object size checking to prevent (some) buffer overflows
-.\" * From: Jakub Jelinek <jakub at redhat dot com>
-.\" * To: gcc-patches at gcc dot gnu dot org
-.\" * Date: Tue, 21 Sep 2004 04:16:40 -0400
-Defining this macro causes some lightweight checks to be performed
-to detect some buffer overflow errors when employing
-various string and memory manipulation functions.
-Not all buffer overflows are detected, just some common cases.
-
-In the current implementation, checks are added for
-calls to
-.BR memcpy (3),
-.BR mempcpy (3),
-.BR memmove (3),
-.BR memset (3),
-.BR stpcpy (3),
-.BR strcpy (3),
-.BR strncpy (3),
-.BR strcat (3),
-.BR strncat (3),
-.BR sprintf (3),
-.BR snprintf (3),
-.BR vsprintf (3),
-.BR vsnprintf (3),
-and
-.BR gets (3).
-
-If
-.B _FORTIFY_SOURCE
-is set to 1, with compiler optimization level 1
-.RI ( "gcc\ \-O1" )
-and above, checks that shouldn't change the behavior of
-conforming programs are performed.
-With
-.B _FORTIFY_SOURCE
-set to 2 some more checking is added, but
-some conforming programs might fail.
-Some of the checks can be performed at compile time,
-and result in compiler warnings;
-other checks take place at run time,
-and result in a run-time error if the check fails.
-
-Use of this macro requires compiler support, available with
-.BR gcc (1)
-since version 4.0.
-.SS Default definitions, implicit definitions, and combining definitions
-.PP
-If no feature test macros are explicitly defined,
-then the following feature test macros are defined by default:
-.BR _BSD_SOURCE
-(in glibc 2.19 and earlier),
-.BR _SVID_SOURCE
-(in glibc 2.19 and earlier),
-.BR _DEFAULT_SOURCE
-(since glibc 2.19),
-.BR _POSIX_SOURCE ,
-and
-.BR _POSIX_C_SOURCE =200809L
-(200112L in glibc versions before 2.10;
-199506L in glibc versions before 2.4;
-199309L in glibc versions before 2.1).
-.PP
-If any of
-.BR __STRICT_ANSI__ ,
-.BR _ISOC99_SOURCE ,
-.BR _POSIX_SOURCE ,
-.BR _POSIX_C_SOURCE ,
-.BR _XOPEN_SOURCE ,
-.BR _XOPEN_SOURCE_EXTENDED ,
-.BR _BSD_SOURCE
-(in glibc 2.19 and earlier),
-or
-.B _SVID_SOURCE
-(in glibc 2.19 and earlier)
-is explicitly defined, then
-.BR _BSD_SOURCE ,
-.BR _SVID_SOURCE ,
-and
-.BR _DEFAULT_SOURCE
-are not defined by default.
-
-If
-.B _POSIX_SOURCE
-and
-.B _POSIX_C_SOURCE
-are not explicitly defined,
-and either
-.B __STRICT_ANSI__
-is not defined or
-.B _XOPEN_SOURCE
-is defined with a value of 500 or more, then
-.IP * 3
-.B _POSIX_SOURCE
-is defined with the value 1; and
-.IP *
-.B _POSIX_C_SOURCE
-is defined with one of the following values:
-.RS 3
-.IP \(bu 3
-2,
-if
-.B _XOPEN_SOURCE
-is defined with a value less than 500;
-.IP \(bu
-199506L,
-if
-.B _XOPEN_SOURCE
-is defined with a value greater than or equal to 500 and less than 600;
-or
-.IP \(bu
-(since glibc 2.4) 200112L,
-if
-.B _XOPEN_SOURCE
-is defined with a value greater than or equal to 600 and less than 700.
-.IP \(bu
-(Since glibc 2.10)
-200809L,
-if
-.B _XOPEN_SOURCE
-is defined with a value greater than or equal to 700.
-.IP \(bu
-Older versions of glibc do not know about the values
-200112L and 200809L for
-.BR _POSIX_C_SOURCE ,
-and the setting of this macro will depend on the glibc version.
-.IP \(bu
-If
-.B _XOPEN_SOURCE
-is undefined, then the setting of
-.B _POSIX_C_SOURCE
-depends on the glibc version:
-199506L, in glibc versions before 2.4;
-200112L, in glibc 2.4 to 2.9; and
-200809L, since glibc 2.10.
-.RE
-.PP
-Multiple macros can be defined; the results are additive.
-.SH CONFORMING TO
-POSIX.1 specifies
-.BR _POSIX_C_SOURCE ,
-.BR _POSIX_SOURCE ,
-and
-.BR _XOPEN_SOURCE .
-.B _XOPEN_SOURCE_EXTENDED
-was specified by XPG4v2 (aka SUSv1).
-
-.B _FILE_OFFSET_BITS
-is not specified by any standard,
-but is employed on some other implementations.
-
-.BR _BSD_SOURCE ,
-.BR _SVID_SOURCE ,
-.BR _DEFAULT_SOURCE ,
-.BR _ATFILE_SOURCE ,
-.BR _GNU_SOURCE ,
-.BR _FORTIFY_SOURCE ,
-.BR _REENTRANT ,
-and
-.B _THREAD_SAFE
-are specific to Linux (glibc).
-.SH NOTES
-.I <features.h>
-is a Linux/glibc-specific header file.
-Other systems have an analogous file, but typically with a different name.
-This header file is automatically included by other header files as
-required: it is not necessary to explicitly include it in order to
-employ feature test macros.
-
-According to which of the above feature test macros are defined,
-.I <features.h>
-internally defines various other macros that are checked by
-other glibc header files.
-These macros have names prefixed by two underscores (e.g.,
-.BR __USE_MISC ).
-Programs should
-.I never
-define these macros directly:
-instead, the appropriate feature test macro(s) from the
-list above should be employed.
-.SH EXAMPLE
-The program below can be used to explore how the various
-feature test macros are set depending on the glibc version
-and what feature test macros are explicitly set.
-The following shell session, on a system with glibc 2.10,
-shows some examples of what we would see:
-.in +4n
-.nf
-
-$ \fBcc ftm.c\fP
-$ \fB./a.out\fP
-_POSIX_SOURCE defined
-_POSIX_C_SOURCE defined: 200809L
-_BSD_SOURCE defined
-_SVID_SOURCE defined
-_ATFILE_SOURCE defined
-$ \fBcc \-D_XOPEN_SOURCE=500 ftm.c\fP
-$ \fB./a.out\fP
-_POSIX_SOURCE defined
-_POSIX_C_SOURCE defined: 199506L
-_XOPEN_SOURCE defined: 500
-$ \fBcc \-D_GNU_SOURCE ftm.c\fP
-$ \fB./a.out\fP
-_POSIX_SOURCE defined
-_POSIX_C_SOURCE defined: 200809L
-_ISOC99_SOURCE defined
-_XOPEN_SOURCE defined: 700
-_XOPEN_SOURCE_EXTENDED defined
-_LARGEFILE64_SOURCE defined
-_BSD_SOURCE defined
-_SVID_SOURCE defined
-_ATFILE_SOURCE defined
-_GNU_SOURCE defined
-.fi
-.in
-.SS Program source
-\&
-.nf
-/* ftm.c */
-
-#include <stdio.h>
-#include <unistd.h>
-#include <stdlib.h>
-
-int
-main(int argc, char *argv[])
-{
-#ifdef _POSIX_SOURCE
- printf("_POSIX_SOURCE defined\\n");
-#endif
-
-#ifdef _POSIX_C_SOURCE
- printf("_POSIX_C_SOURCE defined: %ldL\\n", (long) _POSIX_C_SOURCE);
-#endif
-
-#ifdef _ISOC99_SOURCE
- printf("_ISOC99_SOURCE defined\\n");
-#endif
-
-#ifdef _ISOC11_SOURCE
- printf("_ISOC11_SOURCE defined\\n");
-#endif
-
-#ifdef _XOPEN_SOURCE
- printf("_XOPEN_SOURCE defined: %d\\n", _XOPEN_SOURCE);
-#endif
-
-#ifdef _XOPEN_SOURCE_EXTENDED
- printf("_XOPEN_SOURCE_EXTENDED defined\\n");
-#endif
-
-#ifdef _LARGEFILE64_SOURCE
- printf("_LARGEFILE64_SOURCE defined\\n");
-#endif
-
-#ifdef _FILE_OFFSET_BITS
- printf("_FILE_OFFSET_BITS defined: %d\\n", _FILE_OFFSET_BITS);
-#endif
-
-#ifdef _BSD_SOURCE
- printf("_BSD_SOURCE defined\\n");
-#endif
-
-#ifdef _SVID_SOURCE
- printf("_SVID_SOURCE defined\\n");
-#endif
-
-#ifdef _DEFAULT_SOURCE
- printf("_DEFAULT_SOURCE defined\\n");
-#endif
-
-#ifdef _ATFILE_SOURCE
- printf("_ATFILE_SOURCE defined\\n");
-#endif
-
-#ifdef _GNU_SOURCE
- printf("_GNU_SOURCE defined\\n");
-#endif
-
-#ifdef _REENTRANT
- printf("_REENTRANT defined\\n");
-#endif
-
-#ifdef _THREAD_SAFE
- printf("_THREAD_SAFE defined\\n");
-#endif
-
-#ifdef _FORTIFY_SOURCE
- printf("_FORTIFY_SOURCE defined\\n");
-#endif
-
- exit(EXIT_SUCCESS);
-}
-.fi
-.SH SEE ALSO
-.BR libc (7),
-.BR standards (7)
-
-The section "Feature Test Macros" under
-.IR "info libc" .
-.\" But beware: the info libc document is out of date (Jul 07, mtk)
-
-.I /usr/include/features.h
-.SH COLOPHON
-This page is part of release 3.79 of the Linux
-.I man-pages
-project.
-A description of the project,
-information about reporting bugs,
-and the latest version of this page,
-can be found at
-\%http://www.kernel.org/doc/man\-pages/.
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