path: root/docs/LanguageExtensions.rst
diff options
authorDimitry Andric <dim@FreeBSD.org>2017-01-24 19:18:04 +0000
committerDimitry Andric <dim@FreeBSD.org>2017-01-24 19:18:04 +0000
commit865493b10990f9932c79d135eef448ff418792ab (patch)
tree37718471b885f5ff7effe1fcbcdf114f20b8638b /docs/LanguageExtensions.rst
parent5df539a1004bc4db5c38b33ba3e219595a10ae3c (diff)
Vendor import of clang release_40 branch r292951:vendor/clang/clang-release_40-r292951
Diffstat (limited to 'docs/LanguageExtensions.rst')
1 files changed, 40 insertions, 0 deletions
diff --git a/docs/LanguageExtensions.rst b/docs/LanguageExtensions.rst
index 64e6ffb7f3eb..885ad579ba72 100644
--- a/docs/LanguageExtensions.rst
+++ b/docs/LanguageExtensions.rst
@@ -1776,6 +1776,46 @@ numeric primitives such as frexp. See `LLVM canonicalize intrinsic
<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