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copied!<p>ISO has ratified and published as ISO/IEC 9899:2011 the new C11 (C1x) standard for the C programming language. The major changes from the previous standard (C99), as written in the <a href="http://en.wikipedia.org/wiki/C11_(C_standard_revision)#Changes_from_C99" rel="nofollow">C11 Wikipedia article</a>, are the following:</p> <blockquote> <p>The standard includes several changes to the C99 language and library specifications, such as:</p> <ul> <li>Alignment specification (<code>_Alignas</code> specifier, <code>_Alignof</code> operator, <code>aligned_alloc</code> function, <code><stdalign.h></code> header file)</li> <li>The <code>_Noreturn</code> function specifier</li> <li><p>Type-generic expressions using the <code>_Generic</code> keyword. For example, the following macro <code>cbrt(x)</code> translates to <code>cbrtl(x)</code>, <code>cbrt(x)</code> or <code>cbrtf(x)</code> depending on the type of <code>x</code>:</p> <pre><code> #define cbrt(X) _Generic((X), long double: cbrtl, \ default: cbrt, \ float: cbrtf)(X) </code></pre></li> <li>Multithreading support (<code>_Thread_local</code> storage-class specifier, <code><threads.h></code> header including thread creation/management functions, mutex, condition variable and thread-specific storage functionality, as well as the <code>_Atomic</code> type qualifier and <code><stdatomic.h></code> for uninterruptible object access).</li> <li>Improved Unicode support based on the C Unicode Technical Report ISO/IEC TR 19769:2004 (<code>char16_t</code> and <code>char32_t</code> types for storing UTF-16/UTF-32 encoded data, including conversion functions in <code><uchar.h></code> and the corresponding <code>u</code> and <code>U</code> string literal prefixes, as well as the <code>u8</code> prefix for UTF-8 encoded literals).</li> <li>Removal of the <code>gets</code> function, deprecated in the previous C language standard revision, ISO/IEC 9899:1999/Cor.3:2007(E), in favor of a new safe alternative, <code>gets_s</code>.</li> <li>Bounds-checking interfaces (Annex K).</li> <li>Analyzability features (Annex L).</li> <li>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.</li> <li>Anonymous <em>structures</em> and <em>unions</em>, useful when unions and structures are nested, e.g. in <code>struct T { int tag; union { float x; int n; }; };</code>.</li> <li>Static assertions, which are evaluated during translation at a later phase than <code>#if</code> and <code>#error</code>, when types are understood by the translator.</li> <li>An exclusive create-and-open mode (<code>"…x"</code> suffix) for <code>fopen</code>. This behaves like <code>O_CREAT|O_EXCL</code> in POSIX, which is commonly used for lock files.</li> <li>The <code>quick_exit</code> function as a third way to terminate a program, intended to do at least minimal deinitializition if termination with <code>exit</code> fails.</li> <li>Macros for the construction of complex values (partly because <code>real + imaginary*I</code> might not yield the expected value if <code>imaginary</code> is infinite or NaN).</li> </ul> </blockquote> <p>From the ISO site you can buy the <a href="http://www.iso.org/iso/home/store/catalogue_tc/catalogue_detail.htm?csnumber=57853" rel="nofollow">full published standard</a>. Here is an abstract taken from the ISO site:</p> <blockquote> <p>ISO/IEC 9899:2011 specifies the form and establishes the interpretation of programs written in the C programming language. It specifies</p> <ul> <li>the representation of C programs;</li> <li>the syntax and constraints of the C language;</li> <li>the semantic rules for interpreting C programs;</li> <li>the representation of input data to be processed by C programs;</li> <li>the representation of output data produced by C programs;</li> <li>the restrictions and limits imposed by a conforming implementation of C.</li> </ul> <p>ISO/IEC 9899:2011 does not specify</p> <ul> <li>the mechanism by which C programs are transformed for use by a data-processing system;</li> <li>the mechanism by which C programs are invoked for use by a data-processing system;</li> <li>the mechanism by which input data are transformed for use by a C program;</li> <li>the mechanism by which output data are transformed after being produced by a C program;</li> <li>the size or complexity of a program and its data that will exceed the capacity of any specific data-processing system or the capacity of a particular processor;</li> <li>all minimal requirements of a data-processing system that is capable of supporting a conforming implementation. ISO/IEC 9899:2011 is designed to promote the portability of C programs among a variety of data-processing systems. It is intended for use by implementers and programmers.</li> </ul> </blockquote>

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