stdc11

stdc11 refers to the ISO/IEC 9899:2011 standard for the C programming language, commonly called C11. It is the eleventh edition of the C standard, succeeding C99, and was published in 2011. The update aims to improve safety, portability, and support for modern hardware while preserving backward compatibility with existing C code.

Key language features introduced by stdc11 include type-generic programming via the _Generic keyword, compile-time assertions with _Static_assert, and a non-returning function specifier with _Noreturn. It also adds a thread-local storage qualifier _Thread_local and Unicode support through char16_t and char32_t, along with the <uchar.h> header for related utilities. The _Atomic keyword enables atomic objects, and <stdatomic.h> provides atomic operations and a memory-ordering model.

stdc11 also formalizes optional multi-threading support through the threads library, available in the <threads.h> header. This library provides facilities for creating and joining threads, mutexes, condition variables, thread-local storage, and call-once semantics, enabling portable concurrent programming where supported by the implementation.

Annex K of stdc11 defines a set of bounds-checking interfaces, offering safer alternatives to some standard C library functions. However, Annex K is optional and has not been universally adopted, leading to varying availability of these safer functions across compilers and platforms.

Adoption and legacy: C11 was followed by a minor revision in C17/C18 and, more recently, ongoing work toward newer editions (C23). In practice, compiler and library support for C11 features varies, with most major toolchains providing substantial support for core language features and atomics, while optional components like the threads library and Annex K are inconsistently implemented.