1.\" Copyright (C) 2007, 2010 Gabor Kovesdan. All rights reserved. 2.\" Copyright (C) 2021 Faraz Vahedi <kfv@kfv.io> 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 13.\" THIS SOFTWARE IS PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND 14.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 15.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 16.\" ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE 17.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 18.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 19.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 20.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 21.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 22.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 23.\" SUCH DAMAGE. 24.\" 25.\" $FreeBSD$ 26.\" 27.Dd April 20, 2021 28.Dt C 7 29.Os 30.Sh NAME 31.Nm c , 32.Nm c78 , 33.Nm c89 , 34.Nm c90 , 35.Nm c95 , 36.Nm c99 , 37.Nm c11 , 38.Nm c17 , 39.Nm c2x 40.Nd The C programming language 41.Sh DESCRIPTION 42C is a general purpose programming language, which has a strong connection 43with the UNIX operating system and its derivatives, since the vast 44majority of those systems were written in the C language. 45The C language contains some basic ideas from the BCPL language through 46the B language written by Ken Thompson in 1970 for the DEC PDP-7 machines. 47The development of the UNIX operating system was started on a PDP-7 48machine in assembly language, but it made very difficult to port the existing 49code to other systems. 50.Pp 51In 1972 Dennis M. Ritchie worked out the C programming language for 52further development of the UNIX operating system. 53The idea was to implement only the C compiler for different 54platforms, and implement most part of the operating system 55in the new programming language to simplify the portability between 56different architectures. 57It follows that C is very eligible for (but not limited to) writing 58operating systems and low-level applications. 59.Pp 60The C language did not have a specification or standardized version for 61a long time. 62It went through a lot of changes and improvements for ages. 63In 1978, Brian W. Kernighan and Dennis M. Ritchie published the 64first book about C under the title "The C Programming Language". 65We can think of this book as the first specification of the language. 66This version is often referred as K&R C after the names of the authors. 67Sometimes it is referred as C78, as well, after the publishing year of 68the first edition of the book. 69.Pp 70It is important to notice, that the instruction set of the language is 71limited to the most fundamental elements for simplicity. 72Handling of the standard I/O and such common functions are implemented in 73the libraries shipped with the compiler. 74As these functions are also widely used, it was demanded to include into 75the description what requisites the library should conform to, not just 76strictly the language itself. 77Accordingly, the aforementioned standards cover the library elements, as well. 78The elements of this standard library is still not enough for more 79complicated tasks. 80In this case the provided system calls of the given operating system can be 81used. 82To not lose the portability by using these system calls, the POSIX 83(Portable Operating System Interface) standard evolved. 84It describes what functions should be available to keep portability. 85Note, that POSIX is not a C standard, but an operating system standard 86and thus is beyond the scope of this manual. 87The standards discussed below are all C standards and only cover 88the C programming language and the accompanying library. 89All listed improvements for each standard edition are taken from the official 90standard drafts. 91For further details, check the publicly available drafts or 92purchase the published standards \(em from either ISO or IEC resources. 93.Pp 94After the publication of the book mentioned before, 95the American National Standards Institute (ANSI) started to work on 96standardizing the language, and they announced ANSI X3.159-1989 97in 1989. 98It is usually referred to as ANSI C or C89. 99The main difference in this standard were the function prototypes, 100which is a new way of declaring functions. 101With the old-style function declarations, the compiler was unable to 102check the sanity of the actual parameters at a function call. 103The old syntax was highly error-prone because incompatible parameters 104were hard to detect in the program code and the problem only showed up 105at run-time. 106.Pp 107In 1990, the International Organization for Standardization (ISO) adopted 108the ANSI standard as ISO/IEC 9899:1990 in 1990. 109This is also referred to as ISO C or C90. 110It only contains negligible minor modifications against ANSI C, 111so the two standards often considered to be fully equivalent. 112This was a very important milestone in the history of the C language, but the 113development of the language did not stop. 114.Pp 115The ISO C standard was later extended with an amendment as 116ISO/IEC 9899/AMD1 in 1995. 117This contained, for example, the wide-character support in <wchar.h> and 118<wctype.h>, and also restricted character set support via diagraphs and 119<iso646.h>. 120This amendment is usually referred to as C95. 121Two technical corrigenda were also published: Technical Corrigendum 1 as 122ISO/IEC 9899/COR1 in 1994 and Technical Corrigendum 2 as ISO/IEC 9899/COR2 123in 1996. 124The continuous development and growth made it necessary to work out a new 125standard, which contains the new features and fixes the known defects and 126deficiencies of the language. 127As a result, ISO/IEC 9899:1999 was born in 1999 as the second edition of the 128standard. 129Similarly to the other standards, this is informally named after the 130publication year as C99. 131The improvements include (but are not limited to) the following: 132.Bl -bullet -offset indent 133.It 134digraphs, trigraphs, and alternative spellings for the operators that 135use non-ISO646 characters in <iso646.h> 136.It 137extended multibyte and wide character library support in <wchar.h> and 138<wctype.h> 139.It 140variable length arrays 141.It 142flexible array members 143.It 144complex (and imaginary) number arithmetic support in <complex.h> 145.It 146type-generic math macros in <tgmath.h> 147.It 148the long long int type and library functions 149.It 150remove implicit int type 151.It 152universal character names (\eu and \eU) 153.It 154compound literals 155.It 156remove implicit function declaration 157.It 158BCPL style single-line comments 159.It 160allow mixed declarations and code 161.It 162the vscanf family of functions in <stdio.h> and <wchar.h> 163.It 164allow trailing comma in enum declaration 165.It 166inline functions 167.It 168the snprintf family of functions in <stdio.h> 169.It 170boolean type and macros in <stdbool.h> 171.It 172empty macro arguments 173.It 174_Pragma preprocessing operator 175.It 176__func__ predefined identifier 177.It 178va_copy macro in <stdarg.h> 179.It 180additional strftime conversion specifiers 181.El 182.Pp 183Later in 2011, the third edition of the standard, ISO/IEC 1989:2011, 184commonly referred to as C11 (formerly C1x), came out and replaced the 185second edition by ISO/IEC 9899:1999/COR1:2001, ISO/IEC 9899:1999/COR2:2004, 186and ISO/IEC 9899:1999/COR3:2007. 187The improvements include (but are not limited to) the following: 188.Bl -bullet -offset indent 189.It 190support for multiple threads of execution and atomic operations in <threads.h> 191and <stdatomic.h> 192.It 193additional floating-point characteristic macros in <float.h> 194.It 195querying and specifying alignment of objects in <stdalign.h> and <stdlib.h> 196.It 197Unicode character types and functions in <uchar.h> 198.It 199type-generic expressions 200.It 201static assertions in <assert.h> 202.It 203anonymous structures and unions 204.It 205remove the gets function from <stdio.h> 206.It 207add the aligned_alloc, at_quick_exit, and quick_exit functions in <stdlib.h> 208.El 209.Pp 210C11 was later superseded by ISO/IEC 9899:2018, also known as C17 which was 211prepared in 2017 and published in June 2018 as the fourth edition. 212It incorporates the Technical Corrigendum 1 (ISO/IEC 9899:2011/COR1:2012) 213which was published in 2012. 214It addressed defects and deficiencies in C11 without introducing new features, 215only corrections and clarifications. 216Since there were no major changes in C17, the current standard for 217Programming Language C, is still considered C11 \(em ISO/IEC 9899:2011, published 2182011-12-08. 219.Pp 220The next standard, the fifth, is currently referred to as C2x and is scheduled 221to be adopted by the end of 2021, with a publication date of 2022. 222When published, it will cancel and replace the fourth edition, ISO/IEC 2239899:2018. 224.Pp 225Some useful features have been provided as extensions by some compilers, but 226they cannot be considered as standard features. 227.Pp 228ISO/IEC JTC1/SC22/WG14 committee is responsible for the ISO/IEC 9899, 229C Standard. 230.Sh SEE ALSO 231.Xr c89 1 , 232.Xr c99 1 , 233.Xr cc 1 234.Sh STANDARDS 235.Rs 236.%A ANSI 237.%T X3.159-1989 (aka C89 or ANSI C) 238.Re 239.Pp 240.Rs 241.%A ISO/IEC 242.%T 9899:1990 (aka C90) 243.Re 244.Pp 245.Rs 246.%A ISO/IEC 247.%T 9899:1990/AMD 1:1995, Amendment 1: C Integrity (aka C95) 248.Re 249.Pp 250.Rs 251.%A ISO/IEC 252.%T 9899:1990/COR 1:1994, Technical Corrigendum 1 253.Re 254.Pp 255.Rs 256.%A ISO/IEC 257.%T 9899:1990/COR 2:1996, Technical Corrigendum 2 258.Re 259.Pp 260.Rs 261.%A ISO/IEC 262.%T 9899:1999 (aka C99) 263.Re 264.Pp 265.Rs 266.%A ISO/IEC 267.%T 9899:1999/COR 1:2001, Technical Corrigendum 1 268.Re 269.Pp 270.Rs 271.%A ISO/IEC 272.%T 9899:1999/COR 2:2004, Technical Corrigendum 2 273.Re 274.Pp 275.Rs 276.%A ISO/IEC 277.%T 9899:1999/COR 3:2007, Technical Corrigendum 3 278.Re 279.Pp 280.Rs 281.%A ISO/IEC 282.%T TR 24731-1:2007 (aka bounds-checking interfaces) 283.Re 284.Pp 285.Rs 286.%A ISO/IEC 287.%T TS 18037:2008 (aka, embedded C) 288.Re 289.Pp 290.Rs 291.%A ISO/IEC 292.%T TR 24747:2009 (aka mathematical special functions) 293.Re 294.Pp 295.Rs 296.%A ISO/IEC 297.%T TR 24732:2009 (aka decimal floating-point) 298.Re 299.Pp 300.Rs 301.%A ISO/IEC 302.%T TR 24731-2:2010 (aka dynamic allocation functions) 303.Re 304.Pp 305.Rs 306.%A ISO/IEC 307.%T 9899:2011 (aka C11) 308.Re 309.Pp 310.Rs 311.%A ISO/IEC 312.%T 9899:2011/COR 1:2012, Technical Corrigendum 1 313.Re 314.Pp 315.Rs 316.%A ISO/IEC 317.%T TS 17961:2013 (aka C secure coding rules) 318.Re 319.Pp 320.Rs 321.%A ISO/IEC 322.%T TS 18861-1:2014 (aka binary floating-point) 323.Re 324.Pp 325.Rs 326.%A ISO/IEC 327.%T TS 18861-2:2015 (aka decimal floating-point) 328.Re 329.Pp 330.Rs 331.%A ISO/IEC 332.%T TS 18861-3:2015 (aka interchange and extended types) 333.Re 334.Pp 335.Rs 336.%A ISO/IEC 337.%T TS 18861-4:2015 (aka supplementary functions) 338.Re 339.Pp 340.Rs 341.%A ISO/IEC 342.%T TS 17961:2013/COR 1:2016 (aka C secure coding rules TC1) 343.Re 344.Pp 345.Rs 346.%A ISO/IEC 347.%T TS 18861-5:2016 (aka supplementary attributes) 348.Re 349.Pp 350.Rs 351.%A ISO/IEC 352.%T 9899:2018 (aka C17) 353.Re 354.Sh HISTORY 355This manual page first appeared in 356.Fx 9.0 . 357.Sh AUTHORS 358.An -nosplit 359This manual page was originally written by 360.An Gabor Kovesdan Aq Mt gabor@FreeBSD.org . 361It was updated for 362.Fx 14.0 363by 364.An Faraz Vahedi Aq Mt kfv@kfv.io 365with information about more recent C standards. 366