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author | Richard Smith <richard-llvm@metafoo.co.uk> | 2017-01-20 00:57:59 +0000 |
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committer | Richard Smith <richard-llvm@metafoo.co.uk> | 2017-01-20 00:57:59 +0000 |
commit | 917daab6b641af5a64eede86ae1c9b41c7077959 (patch) | |
tree | be5e89603f1c11090b8b5e9a1e29ed3883d62741 /docs/LanguageExtensions.rst | |
parent | 3e45634a7f951c2306e4b368f9fb8c8d80c48273 (diff) |
Add documentation for constexpr string builtin support.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@292558 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs/LanguageExtensions.rst')
-rw-r--r-- | docs/LanguageExtensions.rst | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/docs/LanguageExtensions.rst b/docs/LanguageExtensions.rst index 64e6ffb7f3..3a86a599a3 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 |