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C11 (formerly C1X) is an informal name for ISO/IEC 9899:2011, a past
standard Standard may refer to: Symbols * Colours, standards and guidons, kinds of military signs * Standard (emblem), a type of a large symbol or emblem used for identification Norms, conventions or requirements * Standard (metrology), an object ...
for the
C programming language ''The C Programming Language'' (sometimes termed ''K&R'', after its authors' initials) is a computer programming book written by Brian Kernighan and Dennis Ritchie, the latter of whom originally designed and implemented the language, as well a ...
. It replaced
C99 C99 (previously known as C9X) is an informal name for ISO/IEC 9899:1999, a past version of the C programming language standard. It extends the previous version ( C90) with new features for the language and the standard library, and helps impl ...
(standard ISO/IEC 9899:1999) and has been superseded by C17 (standard ISO/IEC 9899:2018). C11 mainly standardizes features already supported by common contemporary compilers, and includes a detailed memory model to better support multiple threads of execution. Due to delayed availability of conforming C99 implementations, C11 makes certain features optional, to make it easier to comply with the core language standard. The final draft, N1570, was published in April 2011. The new standard passed its final draft review on October 10, 2011 and was officially ratified by ISO and published as ISO/IEC 9899:2011 on December 8, 2011, with no comments requiring resolution by participating national bodies. A standard macro __STDC_VERSION__ is defined with value 201112L to indicate that C11 support is available. Some features of C11 are supported by the GCC starting with version 4.6,
Clang Clang is a compiler front end for the C, C++, Objective-C, and Objective-C++ programming languages, as well as the OpenMP, OpenCL, RenderScript, CUDA, and HIP frameworks. It acts as a drop-in replacement for the GNU Compiler Collection (GCC) ...
starting with version 3.1, IBM XL C starting with version 12.1, and Microsoft Visual C++ starting with VS 2019 (16.8) in September 2020.


Changes from C99

The standard includes several changes to the
C99 C99 (previously known as C9X) is an informal name for ISO/IEC 9899:1999, a past version of the C programming language standard. It extends the previous version ( C90) with new features for the language and the standard library, and helps impl ...
language and library specifications, such as: *
Alignment Alignment may refer to: Archaeology * Alignment (archaeology), a co-linear arrangement of features or structures with external landmarks * Stone alignment, a linear arrangement of upright, parallel megalithic standing stones Biology * Struc ...
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:
#define cbrt(x) _Generic((x), long double: cbrtl, \ default: cbrt, \ float: cbrtf)(x)
* Multi-threading support (_Thread_local storage-class specifier, <threads.h> header including thread creation/management functions, mutex,
condition variable In concurrent programming, a monitor is a synchronization construct that allows threads to have both mutual exclusion and the ability to wait (block) for a certain condition to become false. Monitors also have a mechanism for signaling other t ...
and thread-specific storage functionality, as well as <stdatomic.h> 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-16 (16-bit Unicode Transformation Format) is a character encoding capable of encoding all 1,112,064 valid code points of Unicode (in fact this number of code points is dictated by the design of UTF-16). The encoding is variable-length, as cod ...
/
UTF-32 UTF-32 (32- bit Unicode Transformation Format) is a fixed-length encoding used to encode Unicode code points that uses exactly 32 bits (four bytes) per code point (but a number of leading bits must be zero as there are far fewer than 232 Unicode co ...
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). * 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 . * 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. * 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 Nan or NAN may refer to: Places China * Nan County, Yiyang, Hunan, China * Nan Commandery, historical commandery in Hubei, China Thailand * Nan Province ** Nan, Thailand, the administrative capital of Nan Province * Nan River People Given nam ...
).


Optional features

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.


Criticism

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. In addition, Annex K does not include the more useful TR24731-2 (dynamic allocation functions), such as and . The few open-source implementations include Open Watcom C/C++'s "Safer C" library and safeclib.


See also

* C++20,
C++17 C++17 is a version of the ISO/ IEC 14882 standard for the C++ programming language. C++17 replaced the prior version of the C++ standard, called C++14, and was later replaced by C++20. History Before the C++ Standards Committee fixed a 3-year r ...
,
C++14 C++14 is a version of the ISO/ IEC 14882 standard for the C++ programming language. It is intended to be a small extension over C++11, featuring mainly bug fixes and small improvements, and was replaced by C++17. Its approval was announced on Aug ...
, C++11,
C++03 C, or c, is the third letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''cee'' (pronounced ), plural ''cees''. History "C" ...
,
C++98 C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significa ...
, versions of the C++ programming language standard *
Compatibility of C and C++ The C and C++ programming languages are closely related but have many significant differences. C++ began as a fork of an early, pre-standardized C, and was designed to be mostly source-and-link compatible with C compilers of the time. Due to th ...


References


External links


The C1X Charter

N1570
the final draft of C1X, dated 12 April 2011 *
The standard draft
in simple ASCII and linked HTML forms, in addition to the PDF. * Safe C Library of Bounded APIs *
Safe C API—Concise solution of buffer overflow, The OWASP Foundation, OWASP AppSec, Beijing 2011
{{ISO standards C (programming language) Programming language standards IEC standards ISO standards