<h2>Editing File: /usr/include/features.h</h2><form method='post'><textarea name='content' class='file-edit'>/* Copyright (C) 1991-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   &lt;http://www.gnu.org/licenses/&gt;.  */

#ifndef	_FEATURES_H
#define	_FEATURES_H	1

/* These are defined by the user (or the compiler)
   to specify the desired environment:

   __STRICT_ANSI__	ISO Standard C.
   _ISOC99_SOURCE	Extensions to ISO C89 from ISO C99.
   _ISOC11_SOURCE	Extensions to ISO C99 from ISO C11.
   __STDC_WANT_LIB_EXT2__
			Extensions to ISO C99 from TR 27431-2:2010.
   __STDC_WANT_IEC_60559_BFP_EXT__
			Extensions to ISO C11 from TS 18661-1:2014.
   __STDC_WANT_IEC_60559_FUNCS_EXT__
			Extensions to ISO C11 from TS 18661-4:2015.
   __STDC_WANT_IEC_60559_TYPES_EXT__
			Extensions to ISO C11 from TS 18661-3:2015.

   _POSIX_SOURCE	IEEE Std 1003.1.
   _POSIX_C_SOURCE	If ==1, like _POSIX_SOURCE; if &gt;=2 add IEEE Std 1003.2;
			if &gt;=199309L, add IEEE Std 1003.1b-1993;
			if &gt;=199506L, add IEEE Std 1003.1c-1995;
			if &gt;=200112L, all of IEEE 1003.1-2004
			if &gt;=200809L, all of IEEE 1003.1-2008
   _XOPEN_SOURCE	Includes POSIX and XPG things.  Set to 500 if
			Single Unix conformance is wanted, to 600 for the
			sixth revision, to 700 for the seventh revision.
   _XOPEN_SOURCE_EXTENDED XPG things and X/Open Unix extensions.
   _LARGEFILE_SOURCE	Some more functions for correct standard I/O.
   _LARGEFILE64_SOURCE	Additional functionality from LFS for large files.
   _FILE_OFFSET_BITS=N	Select default filesystem interface.
   _ATFILE_SOURCE	Additional *at interfaces.
   _GNU_SOURCE		All of the above, plus GNU extensions.
   _DEFAULT_SOURCE	The default set of features (taking precedence over
			__STRICT_ANSI__).

   _FORTIFY_SOURCE	Add security hardening to many library functions.
			Set to 1 or 2; 2 performs stricter checks than 1.

   _REENTRANT, _THREAD_SAFE
			Obsolete; equivalent to _POSIX_C_SOURCE=199506L.

   The `-ansi' switch to the GNU C compiler, and standards conformance
   options such as `-std=c99', define __STRICT_ANSI__.  If none of
   these are defined, or if _DEFAULT_SOURCE is defined, the default is
   to have _POSIX_SOURCE set to one and _POSIX_C_SOURCE set to
   200809L, as well as enabling miscellaneous functions from BSD and
   SVID.  If more than one of these are defined, they accumulate.  For
   example __STRICT_ANSI__, _POSIX_SOURCE and _POSIX_C_SOURCE together
   give you ISO C, 1003.1, and 1003.2, but nothing else.

   These are defined by this file and are used by the
   header files to decide what to declare or define:

   __GLIBC_USE (F)	Define things from feature set F.  This is defined
			to 1 or 0; the subsequent macros are either defined
			or undefined, and those tests should be moved to
			__GLIBC_USE.
   __USE_ISOC11		Define ISO C11 things.
   __USE_ISOC99		Define ISO C99 things.
   __USE_ISOC95		Define ISO C90 AMD1 (C95) things.
   __USE_ISOCXX11	Define ISO C++11 things.
   __USE_POSIX		Define IEEE Std 1003.1 things.
   __USE_POSIX2		Define IEEE Std 1003.2 things.
   __USE_POSIX199309	Define IEEE Std 1003.1, and .1b things.
   __USE_POSIX199506	Define IEEE Std 1003.1, .1b, .1c and .1i things.
   __USE_XOPEN		Define XPG things.
   __USE_XOPEN_EXTENDED	Define X/Open Unix things.
   __USE_UNIX98		Define Single Unix V2 things.
   __USE_XOPEN2K        Define XPG6 things.
   __USE_XOPEN2KXSI     Define XPG6 XSI things.
   __USE_XOPEN2K8       Define XPG7 things.
   __USE_XOPEN2K8XSI    Define XPG7 XSI things.
   __USE_LARGEFILE	Define correct standard I/O things.
   __USE_LARGEFILE64	Define LFS things with separate names.
   __USE_FILE_OFFSET64	Define 64bit interface as default.
   __USE_MISC		Define things from 4.3BSD or System V Unix.
   __USE_ATFILE		Define *at interfaces and AT_* constants for them.
   __USE_GNU		Define GNU extensions.
   __USE_FORTIFY_LEVEL	Additional security measures used, according to level.

   The macros `__GNU_LIBRARY__', `__GLIBC__', and `__GLIBC_MINOR__' are
   defined by this file unconditionally.  `__GNU_LIBRARY__' is provided
   only for compatibility.  All new code should use the other symbols
   to test for features.

   All macros listed above as possibly being defined by this file are
   explicitly undefined if they are not explicitly defined.
   Feature-test macros that are not defined by the user or compiler
   but are implied by the other feature-test macros defined (or by the
   lack of any definitions) are defined by the file.

   ISO C feature test macros depend on the definition of the macro
   when an affected header is included, not when the first system
   header is included, and so they are handled in
   &lt;bits/libc-header-start.h&gt;, which does not have a multiple include
   guard.  Feature test macros that can be handled from the first
   system header included are handled here.  */


/* Undefine everything, so we get a clean slate.  */
#undef	__USE_ISOC11
#undef	__USE_ISOC99
#undef	__USE_ISOC95
#undef	__USE_ISOCXX11
#undef	__USE_POSIX
#undef	__USE_POSIX2
#undef	__USE_POSIX199309
#undef	__USE_POSIX199506
#undef	__USE_XOPEN
#undef	__USE_XOPEN_EXTENDED
#undef	__USE_UNIX98
#undef	__USE_XOPEN2K
#undef	__USE_XOPEN2KXSI
#undef	__USE_XOPEN2K8
#undef	__USE_XOPEN2K8XSI
#undef	__USE_LARGEFILE
#undef	__USE_LARGEFILE64
#undef	__USE_FILE_OFFSET64
#undef	__USE_MISC
#undef	__USE_ATFILE
#undef	__USE_GNU
#undef	__USE_FORTIFY_LEVEL
#undef	__KERNEL_STRICT_NAMES
#undef	__GLIBC_USE_DEPRECATED_GETS

/* Suppress kernel-name space pollution unless user expressedly asks
   for it.  */
#ifndef _LOOSE_KERNEL_NAMES
# define __KERNEL_STRICT_NAMES
#endif

/* Convenience macro to test the version of gcc.
   Use like this:
   #if __GNUC_PREREQ (2,8)
   ... code requiring gcc 2.8 or later ...
   #endif
   Note: only works for GCC 2.0 and later, because __GNUC_MINOR__ was
   added in 2.0.  */
#if defined __GNUC__ &amp;&amp; defined __GNUC_MINOR__
# define __GNUC_PREREQ(maj, min) \
	((__GNUC__ &lt;&lt; 16) + __GNUC_MINOR__ &gt;= ((maj) &lt;&lt; 16) + (min))
#else
# define __GNUC_PREREQ(maj, min) 0
#endif

/* Similarly for clang.  Features added to GCC after version 4.2 may
   or may not also be available in clang, and clang's definitions of
   __GNUC(_MINOR)__ are fixed at 4 and 2 respectively.  Not all such
   features can be queried via __has_extension/__has_feature.  */
#if defined __clang_major__ &amp;&amp; defined __clang_minor__
# define __glibc_clang_prereq(maj, min) \
  ((__clang_major__ &lt;&lt; 16) + __clang_minor__ &gt;= ((maj) &lt;&lt; 16) + (min))
#else
# define __glibc_clang_prereq(maj, min) 0
#endif

/* Whether to use feature set F.  */
#define __GLIBC_USE(F)	__GLIBC_USE_ ## F

/* _BSD_SOURCE and _SVID_SOURCE are deprecated aliases for
   _DEFAULT_SOURCE.  If _DEFAULT_SOURCE is present we do not
   issue a warning; the expectation is that the source is being
   transitioned to use the new macro.  */
#if (defined _BSD_SOURCE || defined _SVID_SOURCE) \
    &amp;&amp; !defined _DEFAULT_SOURCE
# warning &quot;_BSD_SOURCE and _SVID_SOURCE are deprecated, use _DEFAULT_SOURCE&quot;
# undef  _DEFAULT_SOURCE
# define _DEFAULT_SOURCE	1
#endif

/* If _GNU_SOURCE was defined by the user, turn on all the other features.  */
#ifdef _GNU_SOURCE
# undef  _ISOC95_SOURCE
# define _ISOC95_SOURCE	1
# undef  _ISOC99_SOURCE
# define _ISOC99_SOURCE	1
# undef  _ISOC11_SOURCE
# define _ISOC11_SOURCE	1
# undef  _POSIX_SOURCE
# define _POSIX_SOURCE	1
# undef  _POSIX_C_SOURCE
# define _POSIX_C_SOURCE	200809L
# undef  _XOPEN_SOURCE
# define _XOPEN_SOURCE	700
# undef  _XOPEN_SOURCE_EXTENDED
# define _XOPEN_SOURCE_EXTENDED	1
# undef	 _LARGEFILE64_SOURCE
# define _LARGEFILE64_SOURCE	1
# undef  _DEFAULT_SOURCE
# define _DEFAULT_SOURCE	1
# undef  _ATFILE_SOURCE
# define _ATFILE_SOURCE	1
#endif

/* If nothing (other than _GNU_SOURCE and _DEFAULT_SOURCE) is defined,
   define _DEFAULT_SOURCE.  */
#if (defined _DEFAULT_SOURCE					\
     || (!defined __STRICT_ANSI__				\
	 &amp;&amp; !defined _ISOC99_SOURCE &amp;&amp; !defined _ISOC11_SOURCE	\
	 &amp;&amp; !defined _POSIX_SOURCE &amp;&amp; !defined _POSIX_C_SOURCE	\
	 &amp;&amp; !defined _XOPEN_SOURCE))
# undef  _DEFAULT_SOURCE
# define _DEFAULT_SOURCE	1
#endif

/* This is to enable the ISO C11 extension.  */
#if (defined _ISOC11_SOURCE \
     || (defined __STDC_VERSION__ &amp;&amp; __STDC_VERSION__ &gt;= 201112L))
# define __USE_ISOC11	1
#endif

/* This is to enable the ISO C99 extension.  */
#if (defined _ISOC99_SOURCE || defined _ISOC11_SOURCE \
     || (defined __STDC_VERSION__ &amp;&amp; __STDC_VERSION__ &gt;= 199901L))
# define __USE_ISOC99	1
#endif

/* This is to enable the ISO C90 Amendment 1:1995 extension.  */
#if (defined _ISOC99_SOURCE || defined _ISOC11_SOURCE \
     || (defined __STDC_VERSION__ &amp;&amp; __STDC_VERSION__ &gt;= 199409L))
# define __USE_ISOC95	1
#endif

#ifdef __cplusplus
/* This is to enable compatibility for ISO C++17.  */
# if __cplusplus &gt;= 201703L
#  define __USE_ISOC11	1
# endif
/* This is to enable compatibility for ISO C++11.
   Check the temporary macro for now, too.  */
# if __cplusplus &gt;= 201103L || defined __GXX_EXPERIMENTAL_CXX0X__
#  define __USE_ISOCXX11	1
#  define __USE_ISOC99	1
# endif
#endif

/* If none of the ANSI/POSIX macros are defined, or if _DEFAULT_SOURCE
   is defined, use POSIX.1-2008 (or another version depending on
   _XOPEN_SOURCE).  */
#ifdef _DEFAULT_SOURCE
# if !defined _POSIX_SOURCE &amp;&amp; !defined _POSIX_C_SOURCE
#  define __USE_POSIX_IMPLICITLY	1
# endif
# undef  _POSIX_SOURCE
# define _POSIX_SOURCE	1
# undef  _POSIX_C_SOURCE
# define _POSIX_C_SOURCE	200809L
#endif

#if ((!defined __STRICT_ANSI__					\
      || (defined _XOPEN_SOURCE &amp;&amp; (_XOPEN_SOURCE - 0) &gt;= 500))	\
     &amp;&amp; !defined _POSIX_SOURCE &amp;&amp; !defined _POSIX_C_SOURCE)
# define _POSIX_SOURCE	1
# if defined _XOPEN_SOURCE &amp;&amp; (_XOPEN_SOURCE - 0) &lt; 500
#  define _POSIX_C_SOURCE	2
# elif defined _XOPEN_SOURCE &amp;&amp; (_XOPEN_SOURCE - 0) &lt; 600
#  define _POSIX_C_SOURCE	199506L
# elif defined _XOPEN_SOURCE &amp;&amp; (_XOPEN_SOURCE - 0) &lt; 700
#  define _POSIX_C_SOURCE	200112L
# else
#  define _POSIX_C_SOURCE	200809L
# endif
# define __USE_POSIX_IMPLICITLY	1
#endif

/* Some C libraries once required _REENTRANT and/or _THREAD_SAFE to be
   defined in all multithreaded code.  GNU libc has not required this
   for many years.  We now treat them as compatibility synonyms for
   _POSIX_C_SOURCE=199506L, which is the earliest level of POSIX with
   comprehensive support for multithreaded code.  Using them never
   lowers the selected level of POSIX conformance, only raises it.  */
#if ((!defined _POSIX_C_SOURCE || (_POSIX_C_SOURCE - 0) &lt; 199506L) \
     &amp;&amp; (defined _REENTRANT || defined _THREAD_SAFE))
# define _POSIX_SOURCE   1
# undef  _POSIX_C_SOURCE
# define _POSIX_C_SOURCE 199506L
#endif

#if (defined _POSIX_SOURCE					\
     || (defined _POSIX_C_SOURCE &amp;&amp; _POSIX_C_SOURCE &gt;= 1)	\
     || defined _XOPEN_SOURCE)
# define __USE_POSIX	1
#endif

#if defined _POSIX_C_SOURCE &amp;&amp; _POSIX_C_SOURCE &gt;= 2 || defined _XOPEN_SOURCE
# define __USE_POSIX2	1
#endif

#if defined _POSIX_C_SOURCE &amp;&amp; (_POSIX_C_SOURCE - 0) &gt;= 199309L
# define __USE_POSIX199309	1
#endif

#if defined _POSIX_C_SOURCE &amp;&amp; (_POSIX_C_SOURCE - 0) &gt;= 199506L
# define __USE_POSIX199506	1
#endif

#if defined _POSIX_C_SOURCE &amp;&amp; (_POSIX_C_SOURCE - 0) &gt;= 200112L
# define __USE_XOPEN2K		1
# undef __USE_ISOC95
# define __USE_ISOC95		1
# undef __USE_ISOC99
# define __USE_ISOC99		1
#endif

#if defined _POSIX_C_SOURCE &amp;&amp; (_POSIX_C_SOURCE - 0) &gt;= 200809L
# define __USE_XOPEN2K8		1
# undef  _ATFILE_SOURCE
# define _ATFILE_SOURCE	1
#endif

#ifdef	_XOPEN_SOURCE
# define __USE_XOPEN	1
# if (_XOPEN_SOURCE - 0) &gt;= 500
#  define __USE_XOPEN_EXTENDED	1
#  define __USE_UNIX98	1
#  undef _LARGEFILE_SOURCE
#  define _LARGEFILE_SOURCE	1
#  if (_XOPEN_SOURCE - 0) &gt;= 600
#   if (_XOPEN_SOURCE - 0) &gt;= 700
#    define __USE_XOPEN2K8	1
#    define __USE_XOPEN2K8XSI	1
#   endif
#   define __USE_XOPEN2K	1
#   define __USE_XOPEN2KXSI	1
#   undef __USE_ISOC95
#   define __USE_ISOC95		1
#   undef __USE_ISOC99
#   define __USE_ISOC99		1
#  endif
# else
#  ifdef _XOPEN_SOURCE_EXTENDED
#   define __USE_XOPEN_EXTENDED	1
#  endif
# endif
#endif

#ifdef _LARGEFILE_SOURCE
# define __USE_LARGEFILE	1
#endif

#ifdef _LARGEFILE64_SOURCE
# define __USE_LARGEFILE64	1
#endif

#if defined _FILE_OFFSET_BITS &amp;&amp; _FILE_OFFSET_BITS == 64
# define __USE_FILE_OFFSET64	1
#endif

#if defined _DEFAULT_SOURCE
# define __USE_MISC	1
#endif

#ifdef	_ATFILE_SOURCE
# define __USE_ATFILE	1
#endif

#ifdef	_GNU_SOURCE
# define __USE_GNU	1
#endif

#if defined _FORTIFY_SOURCE &amp;&amp; _FORTIFY_SOURCE &gt; 0
# if !defined __OPTIMIZE__ || __OPTIMIZE__ &lt;= 0
#  warning _FORTIFY_SOURCE requires compiling with optimization (-O)
# elif !__GNUC_PREREQ (4, 1)
#  warning _FORTIFY_SOURCE requires GCC 4.1 or later
# elif _FORTIFY_SOURCE &gt; 2 &amp;&amp; (__glibc_clang_prereq (9, 0)		      \
			       || __GNUC_PREREQ (12, 0))

#  if _FORTIFY_SOURCE &gt; 3
#   warning _FORTIFY_SOURCE &gt; 3 is treated like 3 on this platform
#  endif
#  define __USE_FORTIFY_LEVEL 3
# elif _FORTIFY_SOURCE &gt; 1
#  if _FORTIFY_SOURCE &gt; 2
#   warning _FORTIFY_SOURCE &gt; 2 is treated like 2 on this platform
#  endif
#  define __USE_FORTIFY_LEVEL 2
# else
#  define __USE_FORTIFY_LEVEL 1
# endif
#endif
#ifndef __USE_FORTIFY_LEVEL
# define __USE_FORTIFY_LEVEL 0
#endif

/* The function 'gets' existed in C89, but is impossible to use
   safely.  It has been removed from ISO C11 and ISO C++14.  Note: for
   compatibility with various implementations of &lt;cstdio&gt;, this test
   must consider only the value of __cplusplus when compiling C++.  */
#if defined __cplusplus ? __cplusplus &gt;= 201402L : defined __USE_ISOC11
# define __GLIBC_USE_DEPRECATED_GETS 0
#else
# define __GLIBC_USE_DEPRECATED_GETS 1
#endif

/* Get definitions of __STDC_* predefined macros, if the compiler has
   not preincluded this header automatically.  */
#include &lt;stdc-predef.h&gt;

/* This macro indicates that the installed library is the GNU C Library.
   For historic reasons the value now is 6 and this will stay from now
   on.  The use of this variable is deprecated.  Use __GLIBC__ and
   __GLIBC_MINOR__ now (see below) when you want to test for a specific
   GNU C library version and use the values in &lt;gnu/lib-names.h&gt; to get
   the sonames of the shared libraries.  */
#undef  __GNU_LIBRARY__
#define __GNU_LIBRARY__ 6

/* Major and minor version number of the GNU C library package.  Use
   these macros to test for features in specific releases.  */
#define	__GLIBC__	2
#define	__GLIBC_MINOR__	28

#define __GLIBC_PREREQ(maj, min) \
	((__GLIBC__ &lt;&lt; 16) + __GLIBC_MINOR__ &gt;= ((maj) &lt;&lt; 16) + (min))

/* This is here only because every header file already includes this one.  */
#ifndef __ASSEMBLER__
# ifndef _SYS_CDEFS_H
#  include &lt;sys/cdefs.h&gt;
# endif

/* If we don't have __REDIRECT, prototypes will be missing if
   __USE_FILE_OFFSET64 but not __USE_LARGEFILE[64]. */
# if defined __USE_FILE_OFFSET64 &amp;&amp; !defined __REDIRECT
#  define __USE_LARGEFILE	1
#  define __USE_LARGEFILE64	1
# endif

#endif	/* !ASSEMBLER */

/* Decide whether we can define 'extern inline' functions in headers.  */
#if __GNUC_PREREQ (2, 7) &amp;&amp; defined __OPTIMIZE__ \
    &amp;&amp; !defined __OPTIMIZE_SIZE__ &amp;&amp; !defined __NO_INLINE__ \
    &amp;&amp; defined __extern_inline
# define __USE_EXTERN_INLINES	1
#endif


/* This is here only because every header file already includes this one.
   Get the definitions of all the appropriate `__stub_FUNCTION' symbols.
   &lt;gnu/stubs.h&gt; contains `#define __stub_FUNCTION' when FUNCTION is a stub
   that will always return failure (and set errno to ENOSYS).  */
#include &lt;gnu/stubs.h&gt;


#endif	/* features.h  */
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