ef0ba6bcce
Those misspellings were not picked up by igor because they are not present in its list of common spelling errors. Reported by: rpokala
366 lines
11 KiB
Groff
366 lines
11 KiB
Groff
.\" Copyright (C) 2007, 2010 Gabor Kovesdan. All rights reserved.
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.\" Copyright (C) 2021 Faraz Vahedi <kfv@kfv.io>
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd April 20, 2021
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.Dt C 7
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.Os
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.Sh NAME
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.Nm c ,
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.Nm c78 ,
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.Nm c89 ,
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.Nm c90 ,
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.Nm c95 ,
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.Nm c99 ,
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.Nm c11 ,
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.Nm c17 ,
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.Nm c2x
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.Nd The C programming language
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.Sh DESCRIPTION
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C is a general purpose programming language, which has a strong connection
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with the UNIX operating system and its derivatives, since the vast
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majority of those systems were written in the C language.
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The C language contains some basic ideas from the BCPL language through
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the B language written by Ken Thompson in 1970 for the DEC PDP-7 machines.
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The development of the UNIX operating system was started on a PDP-7
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machine in assembly language, but it made very difficult to port the existing
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code to other systems.
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.Pp
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In 1972 Dennis M. Ritchie worked out the C programming language for
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further development of the UNIX operating system.
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The idea was to implement only the C compiler for different
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platforms, and implement most part of the operating system
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in the new programming language to simplify the portability between
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different architectures.
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It follows that C is very eligible for (but not limited to) writing
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operating systems and low-level applications.
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.Pp
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The C language did not have a specification or standardized version for
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a long time.
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It went through a lot of changes and improvements for ages.
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In 1978, Brian W. Kernighan and Dennis M. Ritchie published the
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first book about C under the title "The C Programming Language".
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We can think of this book as the first specification of the language.
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This version is often referred as K&R C after the names of the authors.
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Sometimes it is referred as C78, as well, after the publishing year of
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the first edition of the book.
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.Pp
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It is important to notice, that the instruction set of the language is
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limited to the most fundamental elements for simplicity.
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Handling of the standard I/O and such common functions are implemented in
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the libraries shipped with the compiler.
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As these functions are also widely used, it was demanded to include into
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the description what requisites the library should conform to, not just
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strictly the language itself.
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Accordingly, the aforementioned standards cover the library elements, as well.
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The elements of this standard library is still not enough for more
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complicated tasks.
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In this case the provided system calls of the given operating system can be
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used.
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To not lose the portability by using these system calls, the POSIX
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(Portable Operating System Interface) standard evolved.
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It describes what functions should be available to keep portability.
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Note, that POSIX is not a C standard, but an operating system standard
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and thus is beyond the scope of this manual.
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The standards discussed below are all C standards and only cover
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the C programming language and the accompanying library.
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All listed improvements for each standard edition are taken from the official
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standard drafts.
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For further details, check the publicly available drafts or
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purchase the published standards \(em from either ISO or IEC resources.
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.Pp
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After the publication of the book mentioned before,
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the American National Standards Institute (ANSI) started to work on
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standardizing the language, and they announced ANSI X3.159-1989
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in 1989.
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It is usually referred to as ANSI C or C89.
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The main difference in this standard were the function prototypes,
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which is a new way of declaring functions.
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With the old-style function declarations, the compiler was unable to
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check the sanity of the actual parameters at a function call.
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The old syntax was highly error-prone because incompatible parameters
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were hard to detect in the program code and the problem only showed up
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at run-time.
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.Pp
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In 1990, the International Organization for Standardization (ISO) adopted
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the ANSI standard as ISO/IEC 9899:1990 in 1990.
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This is also referred to as ISO C or C90.
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It only contains negligible minor modifications against ANSI C,
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so the two standards often considered to be fully equivalent.
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This was a very important milestone in the history of the C language, but the
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development of the language did not stop.
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.Pp
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The ISO C standard was later extended with an amendment as
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ISO/IEC 9899/AMD1 in 1995.
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This contained, for example, the wide-character support in <wchar.h> and
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<wctype.h>, and also restricted character set support via diagraphs and
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<iso646.h>.
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This amendment is usually referred to as C95.
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Two technical corrigenda were also published: Technical Corrigendum 1 as
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ISO/IEC 9899/COR1 in 1994 and Technical Corrigendum 2 as ISO/IEC 9899/COR2
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in 1996.
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The continuous development and growth made it necessary to work out a new
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standard, which contains the new features and fixes the known defects and
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deficiencies of the language.
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As a result, ISO/IEC 9899:1999 was born in 1999 as the second edition of the
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standard.
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Similarly to the other standards, this is informally named after the
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publication year as C99.
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The improvements include (but are not limited to) the following:
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.Bl -bullet -offset indent
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.It
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digraphs, trigraphs, and alternative spellings for the operators that
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use non-ISO646 characters in <iso646.h>
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.It
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extended multibyte and wide character library support in <wchar.h> and
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<wctype.h>
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.It
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variable length arrays
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.It
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flexible array members
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.It
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complex (and imaginary) number arithmetic support in <complex.h>
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.It
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type-generic math macros in <tgmath.h>
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.It
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the long long int type and library functions
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.It
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remove implicit int type
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.It
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universal character names (\eu and \eU)
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.It
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compound literals
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.It
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remove implicit function declaration
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.It
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BCPL style single-line comments
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.It
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allow mixed declarations and code
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.It
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the vscanf family of functions in <stdio.h> and <wchar.h>
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.It
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allow trailing comma in enum declaration
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.It
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inline functions
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.It
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the snprintf family of functions in <stdio.h>
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.It
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boolean type and macros in <stdbool.h>
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.It
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empty macro arguments
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.It
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_Pragma preprocessing operator
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.It
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__func__ predefined identifier
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.It
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va_copy macro in <stdarg.h>
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.It
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additional strftime conversion specifiers
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.El
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.Pp
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Later in 2011, the third edition of the standard, ISO/IEC 1989:2011,
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commonly referred to as C11 (formerly C1x), came out and replaced the
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second edition by ISO/IEC 9899:1999/COR1:2001, ISO/IEC 9899:1999/COR2:2004,
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and ISO/IEC 9899:1999/COR3:2007.
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The improvements include (but are not limited to) the following:
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.Bl -bullet -offset indent
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.It
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support for multiple threads of execution and atomic operations in <threads.h>
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and <stdatomic.h>
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.It
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additional floating-point characteristic macros in <float.h>
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.It
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querying and specifying alignment of objects in <stdalign.h> and <stdlib.h>
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.It
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Unicode character types and functions in <uchar.h>
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.It
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type-generic expressions
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.It
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static assertions in <assert.h>
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.It
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anonymous structures and unions
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.It
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remove the gets function from <stdio.h>
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.It
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add the aligned_alloc, at_quick_exit, and quick_exit functions in <stdlib.h>
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.El
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.Pp
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C11 was later superseded by ISO/IEC 9899:2018, also known as C17 which was
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prepared in 2017 and published in June 2018 as the fourth edition.
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It incorporates the Technical Corrigendum 1 (ISO/IEC 9899:2011/COR1:2012)
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which was published in 2012.
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It addressed defects and deficiencies in C11 without introducing new features,
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only corrections and clarifications.
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Since there were no major changes in C17, the current standard for
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Programming Language C, is still considered C11 \(em ISO/IEC 9899:2011, published
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2011-12-08.
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.Pp
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The next standard, the fifth, is currently referred to as C2x and is scheduled
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to be adopted by the end of 2021, with a publication date of 2022.
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When published, it will cancel and replace the fourth edition, ISO/IEC
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9899:2018.
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.Pp
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Some useful features have been provided as extensions by some compilers, but
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they cannot be considered as standard features.
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.Pp
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ISO/IEC JTC1/SC22/WG14 committee is responsible for the ISO/IEC 9899,
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C Standard.
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.Sh SEE ALSO
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.Xr c89 1 ,
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.Xr c99 1 ,
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.Xr cc 1
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.Sh STANDARDS
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.Rs
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.%A ANSI
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.%T X3.159-1989 (aka C89 or ANSI C)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:1990 (aka C90)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:1990/AMD 1:1995, Amendment 1: C Integrity (aka C95)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:1990/COR 1:1994, Technical Corrigendum 1
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:1990/COR 2:1996, Technical Corrigendum 2
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:1999 (aka C99)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:1999/COR 1:2001, Technical Corrigendum 1
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:1999/COR 2:2004, Technical Corrigendum 2
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:1999/COR 3:2007, Technical Corrigendum 3
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TR 24731-1:2007 (aka bounds-checking interfaces)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TS 18037:2008 (aka, embedded C)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TR 24747:2009 (aka mathematical special functions)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TR 24732:2009 (aka decimal floating-point)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TR 24731-2:2010 (aka dynamic allocation functions)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:2011 (aka C11)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:2011/COR 1:2012, Technical Corrigendum 1
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TS 17961:2013 (aka C secure coding rules)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TS 18861-1:2014 (aka binary floating-point)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TS 18861-2:2015 (aka decimal floating-point)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TS 18861-3:2015 (aka interchange and extended types)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TS 18861-4:2015 (aka supplementary functions)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TS 17961:2013/COR 1:2016 (aka C secure coding rules TC1)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T TS 18861-5:2016 (aka supplementary attributes)
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.Re
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.Pp
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.Rs
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.%A ISO/IEC
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.%T 9899:2018 (aka C17)
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.Re
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.Sh HISTORY
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This manual page first appeared in
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.Fx 9.0 .
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.Sh AUTHORS
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.An -nosplit
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This manual page was originally written by
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.An Gabor Kovesdan Aq Mt gabor@FreeBSD.org .
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It was updated for
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.Fx 14.0
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by
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.An Faraz Vahedi Aq Mt kfv@kfv.io
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with information about more recent C standards.
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