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=======================
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Clang 3.4 Release Notes
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=======================
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.. contents::
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:local:
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:depth: 2
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Introduction
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============
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This document contains the release notes for the Clang C/C++/Objective-C
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frontend, part of the LLVM Compiler Infrastructure, release 3.4. Here we
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describe the status of Clang in some detail, including major
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improvements from the previous release and new feature work. For the
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general LLVM release notes, see `the LLVM
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documentation <http://llvm.org/docs/ReleaseNotes.html>`_. All LLVM
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releases may be downloaded from the `LLVM releases web
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site <http://llvm.org/releases/>`_.
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For more information about Clang or LLVM, including information about
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the latest release, please check out the main `Clang Web
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Site <http://clang.llvm.org>`_ or the `LLVM Web
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Site <http://llvm.org>`_.
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Note that if you are reading this file from a Subversion checkout or the
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main Clang web page, this document applies to the *next* release, not
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the current one. To see the release notes for a specific release, please
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see the `releases page <http://llvm.org/releases/>`_.
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What's New in Clang 3.4?
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========================
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Some of the major new features and improvements to Clang are listed
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here. Generic improvements to Clang as a whole or to its underlying
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infrastructure are described first, followed by language-specific
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sections with improvements to Clang's support for those languages.
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Last release which will build as C++98
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--------------------------------------
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This is expected to be the last release of Clang which compiles using a C++98
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toolchain. We expect to start using some C++11 features in Clang starting after
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this release. That said, we are committed to supporting a reasonable set of
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modern C++ toolchains as the host compiler on all of the platforms. This will
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at least include Visual Studio 2012 on Windows, and Clang 3.1 or GCC 4.7.x on
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Mac and Linux. The final set of compilers (and the C++11 features they support)
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is not set in stone, but we wanted users of Clang to have a heads up that the
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next release will involve a substantial change in the host toolchain
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requirements.
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Note that this change is part of a change for the entire LLVM project, not just
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Clang.
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Major New Features
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------------------
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Improvements to Clang's diagnostics
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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Clang's diagnostics are constantly being improved to catch more issues,
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explain them more clearly, and provide more accurate source information
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about them. The improvements since the 3.3 release include:
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- -Wheader-guard warns on mismatches between the #ifndef and #define lines
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in a header guard.
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.. code-block:: c
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#ifndef multiple
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#define multi
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#endif
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returns
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`warning: 'multiple' is used as a header guard here, followed by #define of a different macro [-Wheader-guard]`
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- -Wlogical-not-parentheses warns when a logical not ('!') only applies to the
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left-hand side of a comparison. This warning is part of -Wparentheses.
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.. code-block:: c++
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int i1 = 0, i2 = 1;
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bool ret;
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ret = !i1 == i2;
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returns
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`warning: logical not is only applied to the left hand side of this comparison [-Wlogical-not-parentheses]`
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- Boolean increment, a deprecated feature, has own warning flag
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-Wdeprecated-increment-bool, and is still part of -Wdeprecated.
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- Clang errors on builtin enum increments and decrements.
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.. code-block:: c++
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enum A { A1, A2 };
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void test() {
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A a;
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a++;
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}
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returns
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`error: must use 'enum' tag to refer to type 'A'`
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- -Wloop-analysis now warns on for-loops which have the same increment or
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decrement in the loop header as the last statement in the loop.
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.. code-block:: c
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void foo(char *a, char *b, unsigned c) {
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for (unsigned i = 0; i < c; ++i) {
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a[i] = b[i];
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++i;
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}
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}
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returns
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`warning: variable 'i' is incremented both in the loop header and in the loop body [-Wloop-analysis]`
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- -Wuninitialized now performs checking across field initializers to detect
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when one field in used uninitialized in another field initialization.
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.. code-block:: c++
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class A {
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int x;
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int y;
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A() : x(y) {}
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};
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returns
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`warning: field 'y' is uninitialized when used here [-Wuninitialized]`
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- Clang can detect initializer list use inside a macro and suggest parentheses
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if possible to fix.
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- Many improvements to Clang's typo correction facilities, such as:
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+ Adding global namespace qualifiers so that corrections can refer to shadowed
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or otherwise ambiguous or unreachable namespaces.
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+ Including accessible class members in the set of typo correction candidates,
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so that corrections requiring a class name in the name specifier are now
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possible.
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+ Allowing typo corrections that involve removing a name specifier.
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+ In some situations, correcting function names when a function was given the
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wrong number of arguments, including situations where the original function
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name was correct but was shadowed by a lexically closer function with the
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same name yet took a different number of arguments.
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+ Offering typo suggestions for 'using' declarations.
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+ Providing better diagnostics and fixit suggestions in more situations when
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a '->' was used instead of '.' or vice versa.
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+ Providing more relevant suggestions for typos followed by '.' or '='.
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+ Various performance improvements when searching for typo correction
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candidates.
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- `LeakSanitizer <LeakSanitizer.html>`_ is an experimental memory leak detector
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which can be combined with AddressSanitizer.
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New Compiler Flags
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------------------
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- Clang no longer special cases -O4 to enable lto. Explicitly pass -flto to
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enable it.
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- Clang no longer fails on >= -O5. These flags are mapped to -O3 instead.
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- Command line "clang -O3 -flto a.c -c" and "clang -emit-llvm a.c -c"
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are no longer equivalent.
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- Clang now errors on unknown -m flags (``-munknown-to-clang``),
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unknown -f flags (``-funknown-to-clang``) and unknown
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options (``-what-is-this``).
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C Language Changes in Clang
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---------------------------
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- Added new checked arithmetic builtins for security critical applications.
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C++ Language Changes in Clang
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-----------------------------
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- Fixed an ABI regression, introduced in Clang 3.2, which affected
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member offsets for classes inheriting from certain classes with tail padding.
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See PR16537.
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- Clang 3.4 supports the 2013-08-28 draft of the ISO WG21 SG10 feature test
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macro recommendations. These aim to provide a portable method to determine
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whether a compiler supports a language feature, much like Clang's
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|has_feature macro|_.
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.. |has_feature macro| replace:: ``__has_feature`` macro
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.. _has_feature macro: LanguageExtensions.html#has-feature-and-has-extension
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C++1y Feature Support
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^^^^^^^^^^^^^^^^^^^^^
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Clang 3.4 supports all the features in the current working draft of the
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upcoming C++ standard, provisionally named C++1y. Support for the following
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major new features has been added since Clang 3.3:
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- Generic lambdas and initialized lambda captures.
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- Deduced function return types (``auto f() { return 0; }``).
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- Generalized ``constexpr`` support (variable mutation and loops).
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- Variable templates and static data member templates.
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- Use of ``'`` as a digit separator in numeric literals.
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- Support for sized ``::operator delete`` functions.
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In addition, ``[[deprecated]]`` is now accepted as a synonym for Clang's
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existing ``deprecated`` attribute.
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Use ``-std=c++1y`` to enable C++1y mode.
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OpenCL C Language Changes in Clang
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----------------------------------
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- OpenCL C "long" now always has a size of 64 bit, and all OpenCL C
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types are aligned as specified in the OpenCL C standard. Also,
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"char" is now always signed.
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Internal API Changes
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--------------------
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These are major API changes that have happened since the 3.3 release of
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Clang. If upgrading an external codebase that uses Clang as a library,
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this section should help get you past the largest hurdles of upgrading.
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Wide Character Types
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^^^^^^^^^^^^^^^^^^^^
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The ASTContext class now keeps track of two different types for wide character
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types: WCharTy and WideCharTy. WCharTy represents the built-in wchar_t type
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available in C++. WideCharTy is the type used for wide character literals; in
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C++ it is the same as WCharTy, but in C99, where wchar_t is a typedef, it is an
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integer type.
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Static Analyzer
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---------------
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The static analyzer has been greatly improved. This impacts the overall analyzer quality and reduces a number of false positives.
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In particular, this release provides enhanced C++ support, reasoning about initializer lists, zeroing constructors, noreturn destructors and modeling of destructor calls on calls to delete.
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Clang Format
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------------
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Clang now includes a new tool ``clang-format`` which can be used to
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automatically format C, C++ and Objective-C source code. ``clang-format``
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automatically chooses linebreaks and indentation and can be easily integrated
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into editors, IDEs and version control systems. It supports several pre-defined
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styles as well as precise style control using a multitude of formatting
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options. ``clang-format`` itself is just a thin wrapper around a library which
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can also be used directly from code refactoring and code translation tools.
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More information can be found on `Clang Format's
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site <http://clang.llvm.org/docs/ClangFormat.html>`_.
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Windows Support
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---------------
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- `clang-cl <UsersManual.html#clang-cl>`_ provides a new driver mode that is
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designed for compatibility with Visual Studio's compiler, cl.exe. This driver
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mode makes Clang accept the same kind of command-line options as cl.exe. The
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installer will attempt to expose clang-cl in any Visual Studio installations
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on the system as a Platform Toolset, e.g. "LLVM-vs2012". clang-cl targets the
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Microsoft ABI by default. Please note that this driver mode and compatibility
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with the MS ABI is highly experimental.
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Python Binding Changes
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----------------------
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The following methods have been added:
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Significant Known Problems
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==========================
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Additional Information
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======================
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A wide variety of additional information is available on the `Clang web
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page <http://clang.llvm.org/>`_. The web page contains versions of the
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API documentation which are up-to-date with the Subversion revision of
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the source code. You can access versions of these documents specific to
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this release by going into the "``clang/docs/``" directory in the Clang
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tree.
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If you have any questions or comments about Clang, please feel free to
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contact us via the `mailing
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list <http://lists.cs.uiuc.edu/mailman/listinfo/cfe-dev>`_.
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