C11 (C standard revision)

The standard includes several changes to the C99 language and library specifications, such as

• Alignment specification (_Alignas specifier, _Alignof operator, aligned_alloc function, <stdalign.h> header)
• The _Noreturn function specifier and the <stdnoreturn.h> header
• Type-generic expressions using the _Generic keyword. For example, the following macro cbrt(x) translates to cbrtl(x), cbrt(x) or cbrtf(x) depending on the type of x:

• Multi-threading support (_Thread_local storage-class specifier, <threads.h> header including thread creation/management functions, mutex, condition variable and thread-specific storage functionality, as well as <stdatomic.h>{{cite web|url=http://en.cppreference.com/w/c/atomic|title=Atomic operations library - cppreference.com|website=en.cppreference.com}} for atomic operations supporting the C11 memory model).
• Improved Unicode support based on the C Unicode Technical Report ISO/IEC TR 19769:2004 (char16_t and char32_t types for storing UTF-16/UTF-32 encoded data, including conversion functions in <uchar.h> and the corresponding u and U string literal prefixes, as well as the u8 prefix for UTF-8 encoded literals).
• Removal of the gets function (in favor of safer fgets), which was deprecated in the previous C language standard revision, ISO/IEC 9899:1999/Cor.3:2007(E).
• Bounds-checking interfaces (Annex K).{{cite web|last=Berin Babcock-McConnell|title=API02-C. Functions that read or write to or from an array should take an argument to specify the source or target size|url=https://www.securecoding.cert.org/confluence/display/c/API02-C.+Functions+that+read+or+write+to+or+from+an+array+should+take+an+argument+to+specify+the+source+or+target+size}}
• Analyzability features (Annex L).
• More macros for querying the characteristics of floating-point types, concerning subnormal floating-point numbers and the number of decimal digits the type is able to store.
• Anonymous structures and unions, useful when unions and structures are nested, e.g. in {{code|2=c|struct T { int tag; union { float x; int n; }; };}}.
• Static assertions, which are evaluated during translation at a later phase than #if and #error, when types are understood by the translator.
• An exclusive create-and-open mode ("…x" suffix) for fopen. This behaves like O_CREAT|O_EXCL in POSIX, which is commonly used for lock files.
• The quick_exit function as a third way to terminate a program, intended to do at least minimal deinitialization.{{cite web|url=http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1327.htm|title=Abandoning a Process|website=www.open-std.org}}
• A new timespec_get function and corresponding structure in <time.h> with a degree of POSIX compatibility.
• Macros for the construction of complex values (partly because real + imaginary*I might not yield the expected value if imaginary is infinite or NaN).

The new revision allows implementations to not support certain parts of the standard — including some that had been mandatory to support in the 1999 revision. Programs can use predefined macros to determine whether an implementation supports a certain feature or not.

Some features of C11 are supported by the GCC starting with version 4.6,{{cite web|url=https://gcc.gnu.org/gcc-4.6/changes.html#c|title=GCC 4.6 Release Series — Changes, New Features, and Fixes - GNU Project - Free Software Foundation (FSF)|website=gcc.gnu.org}} Clang starting with version 3.1,{{cite web|url=http://llvm.org/releases/3.1/docs/ClangReleaseNotes.html#cchanges|title=Clang 3.1 Release Notes|website=llvm.org}} IBM XL C starting with version 12.1,{{cite web|url=http://www.ibm.com/developerworks/rational/library/support-iso-c11/index.html|title=Support for ISO C11 added to IBM XL C/C++ compilers|date=17 April 2014|website=www.ibm.com}} and Microsoft Visual C++ starting with VS 2019 (16.8){{cite web|url=https://devblogs.microsoft.com/cppblog/c11-and-c17-standard-support-arriving-in-msvc/|title=C11 and C17 Standard Support Arriving in MSVC|date=14 September 2020|website=devblogs.microsoft.com}} in September 2020.

{{See also|C string handling#Replacements}}

The optional bounds-checking interfaces (Annex K) remain controversial and have not been widely implemented, and their deprecation or removal from the next standard revision has been proposed. Even Microsoft, a main proponent of this interface, does not conform to the definition.{{cite web |last1=Leffler |first1=Jonathan |title=c - Do you use the TR 24731 'safe' functions? |url=https://stackoverflow.com/a/373911 |website=Stack Overflow}} In addition, Annex K does not include the more useful TR24731-2 (dynamic allocation functions), such as {{code|vasprintf}} and {{code|open_memstream}}.{{cite web |title=c - Do you use the TR 24731 'safe' functions? |url=https://stackoverflow.com/a/17353714 |website=Stack Overflow}} The few open-source implementations include Open Watcom C/C++'s "Safer C" library{{cite web|url=http://openwatcom.org/index.php/Safer_C_Library|title=Safer C Library - Open Watcom|date=3 May 2015|archive-url=https://web.archive.org/web/20150503192244/http://openwatcom.org/index.php/Safer_C_Library|archive-date=2015-05-03}} and safeclib.{{cite web |title=safec: Safe C Library - README |url=https://rurban.github.io/safeclib/doc/safec-3.5.2/index.html |website=rurban.github.io}}

{{Portal|Computer programming}}

• C++23, C++20, C++17, C++14, C++11, C++03, C++98, versions of the C++ programming language standard
• Compatibility of C and C++

{{reflist|refs=

{{cite web|url=http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1464.htm|title=Creation of complex value|website=www.open-std.org}}

[http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1516.pdf WG14 N1516 Committee Draft — October 4, 2010]

[http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf WG14 N1570 Committee Draft — April 12, 2011]

{{cite web|url=http://www.open-std.org/JTC1/SC22/wg14/www/docs/n1250.pdf|title=WG14 N1250 The C1X Charter}}

ISO 9899:1999 6.10.8 Predefined macro names

[http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1548.pdf WG14 N1548 Committee Draft — December 2, 2010] 6.10.8.3 Conditional feature macros

{{cite web|url=http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1286.pdf|title=WG14 N1286 — "On Support for TR-19769 and New Character Types", Nick Stoughton, Larry Dwyer}}

{{cite web|url=http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1969.htm|title=N1969 — Updated Field Experience With Annex K — Bounds Checking Interfaces|website=www.open-std.org}}

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• [https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf N1570] (working draft of C11 standard); WG14; 2011. ([https://port70.net/~nsz/c/c11 HTML and ASCII versions])
• [https://www.iso.org/standard/57853.html ISO/IEC 9899:2011] (official C11 standard); ISO; 2011.
• {{cite journal|last=Plum|first=Thomas|date=April 6, 2012|title=C Finally Gets A New Standard|journal=Dr. Dobb's Journal|url=http://drdobbs.com/cpp/232800444}}
• [https://web.archive.org/web/20131203031224/http://www.owasp.org.cn/OWASP_Conference/2011/17_.pdf Safe C API—Concise solution of buffer overflow, The OWASP Foundation, OWASP AppSec, Beijing 2011 ]

• [https://www.open-std.org/jtc1/sc22/wg14/www/wg14_document_log.htm C Language Working Group 14 (WG14) Documents]
• [http://www.open-std.org/JTC1/SC22/wg14/www/docs/n1250.pdf C1X Charter] - WG14
• Safe C Library of Bounded APIs

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