Author: rsmith Date: Thu Jan 19 18:57:59 2017 New Revision: 292558 URL: http://llvm.org/viewvc/llvm-project?rev=292558&view=rev Log: Add documentation for constexpr string builtin support.
Modified: cfe/trunk/docs/LanguageExtensions.rst Modified: cfe/trunk/docs/LanguageExtensions.rst URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/docs/LanguageExtensions.rst?rev=292558&r1=292557&r2=292558&view=diff ============================================================================== --- cfe/trunk/docs/LanguageExtensions.rst (original) +++ cfe/trunk/docs/LanguageExtensions.rst Thu Jan 19 18:57:59 2017 @@ -1776,6 +1776,46 @@ numeric primitives such as frexp. See `L <http://llvm.org/docs/LangRef.html#llvm-canonicalize-intrinsic>`_ for more information on the semantics. +String builtins +--------------- + +Clang provides constant expression evaluation support for builtins forms of +the following functions from the C standard library ``<strings.h>`` header: + +* ``memchr`` +* ``memcmp`` +* ``strchr`` +* ``strcmp`` +* ``strlen`` +* ``strncmp`` +* ``wcschr`` +* ``wcscmp`` +* ``wcslen`` +* ``wcsncmp`` +* ``wmemchr`` +* ``wmemcmp`` + +In each case, the builtin form has the name of the C library function prefixed +by ``__builtin``. Example: + +.. code-block:: c + + void *p = __builtin_memchr("foobar", 'b', 5); + +In addition to the above, one further builtin is provided: + +.. code-block:: c + + char *__builtin_char_memchr(const char *haystack, int needle, size_t size); + +``__builtin_char_memchr(a, b, c)`` is identical to +``(char*)__builtin_memchr(a, b, c)`` except that its use is permitted within +constant expressions in C++11 onwards (where a cast from ``void*`` to ``char*`` +is disallowed in general). + +Support for constant expression evaluation for the above builtins be detected +with ``__has_feature(cxx_constexpr_string_builtins)``. + .. _langext-__c11_atomic: __c11_atomic builtins _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits