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01eb99ac7bb111520d011748fb9fff176d2e64d7
libcxx/docs/index.rst
Eric Fiselier 01eb99ac7b Implement a throwing version of _LIBCPP_ASSERT. 
This patch implements changes to allow _LIBCPP_ASSERT to throw on failure
instead of aborting. The main changes needed to do this are:

1. Change _LIBCPP_ASSERT to call a handler via a replacable function pointer
   instead of calling abort directly. Additionally this patch implements two
   handler functions, one which aborts and another that throws an exception.

2. Add _NOEXCEPT_DEBUG macro for disabling noexcept spec on function which
   contain _LIBCPP_ASSERT. This is required in order to prevent assertion
   failures throwing through a noexcept function. This macro has no effect
   unless _LIBCPP_DEBUG_USE_EXCEPTIONS is defined.

Having a non-aborting _LIBCPP_ASSERT is very important to allow sane testing of
debug mode. Currently we can only have one test case per file, since the test
case will cause the program to abort. Testing debug mode this way would require
thousands of test files, most of which would be 95% boiler plate. I don't think
this is a feasible strategy. Fortunately using a throwing debug handler solves
these issues.

Additionally this patch rewrites the documentation for debug mode.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@290651 91177308-0d34-0410-b5e6-96231b3b80d8
2016-12-28 04:58:52 +00:00

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.. _index:
=============================
"libc++" C++ Standard Library
=============================
Overview
========
libc++ is a new implementation of the C++ standard library, targeting C++11.
* Features and Goals
* Correctness as defined by the C++11 standard.
* Fast execution.
* Minimal memory use.
* Fast compile times.
* ABI compatibility with gcc's libstdc++ for some low-level features
such as exception objects, rtti and memory allocation.
* Extensive unit tests.
* Design and Implementation:
* Extensive unit tests
* Internal linker model can be dumped/read to textual format
* Additional linking features can be plugged in as "passes"
* OS specific and CPU specific code factored out
Getting Started with libc++
---------------------------
.. toctree::
:maxdepth: 2
UsingLibcxx
BuildingLibcxx
TestingLibcxx
Current Status
--------------
After its initial introduction, many people have asked "why start a new
library instead of contributing to an existing library?" (like Apache's
libstdcxx, GNU's libstdc++, STLport, etc). There are many contributing
reasons, but some of the major ones are:
* From years of experience (including having implemented the standard
library before), we've learned many things about implementing
the standard containers which require ABI breakage and fundamental changes
to how they are implemented. For example, it is generally accepted that
building std::string using the "short string optimization" instead of
using Copy On Write (COW) is a superior approach for multicore
machines (particularly in C++11, which has rvalue references). Breaking
ABI compatibility with old versions of the library was
determined to be critical to achieving the performance goals of
libc++.
* Mainline libstdc++ has switched to GPL3, a license which the developers
of libc++ cannot use. libstdc++ 4.2 (the last GPL2 version) could be
independently extended to support C++11, but this would be a fork of the
codebase (which is often seen as worse for a project than starting a new
independent one). Another problem with libstdc++ is that it is tightly
integrated with G++ development, tending to be tied fairly closely to the
matching version of G++.
* STLport and the Apache libstdcxx library are two other popular
candidates, but both lack C++11 support. Our experience (and the
experience of libstdc++ developers) is that adding support for C++11 (in
particular rvalue references and move-only types) requires changes to
almost every class and function, essentially amounting to a rewrite.
Faced with a rewrite, we decided to start from scratch and evaluate every
design decision from first principles based on experience.
Further, both projects are apparently abandoned: STLport 5.2.1 was
released in Oct'08, and STDCXX 4.2.1 in May'08.
Platform and Compiler Support
-----------------------------
libc++ is known to work on the following platforms, using gcc-4.2 and
clang (lack of C++11 language support disables some functionality).
Note that functionality provided by ``<atomic>`` is only functional with clang
and GCC.
============ ==================== ============ ========================
OS Arch Compilers ABI Library
============ ==================== ============ ========================
Mac OS X i386, x86_64 Clang, GCC libc++abi
FreeBSD 10+ i386, x86_64, ARM Clang, GCC libcxxrt, libc++abi
Linux i386, x86_64 Clang, GCC libc++abi
============ ==================== ============ ========================
The following minimum compiler versions are strongly recommended.
* Clang 3.5 and above
* GCC 4.7 and above.
Anything older *may* work.
C++ Dialect Support
---------------------
* C++11 - Complete
* `C++14 - Complete <http://libcxx.llvm.org/cxx1y_status.html>`__
* `C++1z - In Progress <http://libcxx.llvm.org/cxx1z_status.html>`__
* `Post C++14 Technical Specifications - In Progress <http://libcxx.llvm.org/ts1z_status.html>`__
Notes and Known Issues
----------------------
This list contains known issues with libc++
* Building libc++ with ``-fno-rtti`` is not supported. However
linking against it with ``-fno-rtti`` is supported.
* On OS X v10.8 and older the CMake option ``-DLIBCXX_LIBCPPABI_VERSION=""``
must be used during configuration.
A full list of currently open libc++ bugs can be `found here`__.
.. __: https://llvm.org/bugs/buglist.cgi?component=All%20Bugs&product=libc%2B%2B&query_format=advanced&resolution=---&order=changeddate%20DESC%2Cassigned_to%20DESC%2Cbug_status%2Cpriority%2Cbug_id&list_id=74184
Design Documents
----------------
.. toctree::
:maxdepth: 1
DesignDocs/DebugMode
DesignDocs/CapturingConfigInfo
DesignDocs/ABIVersioning
DesignDocs/VisibilityMacros
* `<atomic> design <http://libcxx.llvm.org/atomic_design.html>`_
* `<type_traits> design <http://libcxx.llvm.org/type_traits_design.html>`_
* `Status of debug mode <http://libcxx.llvm.org/debug_mode.html>`_
* `Notes by Marshall Clow`__
.. __: https://cplusplusmusings.wordpress.com/2012/07/05/clang-and-standard-libraries-on-mac-os-x/
Build Bots and Test Coverage
----------------------------
* `LLVM Buildbot Builders <http://lab.llvm.org:8011/console>`_
* `Apple Jenkins Builders <http://lab.llvm.org:8080/green/view/Libcxx/>`_
* `EricWF's Nightly Builders <http://ds2.efcs.ca:8080/console>`_
* `Code Coverage Results <http://efcs.ca/libcxx-coverage>`_
Getting Involved
================
First please review our `Developer's Policy <http://llvm.org/docs/DeveloperPolicy.html>`__
and `Getting started with LLVM <http://llvm.org/docs/GettingStarted.html>`__.
**Bug Reports**
If you think you've found a bug in libc++, please report it using
the `LLVM Bugzilla`_. If you're not sure, you
can post a message to the `cfe-dev mailing list`_ or on IRC.
Please include "libc++" in your subject.
**Patches**
If you want to contribute a patch to libc++, the best place for that is
`Phabricator <http://llvm.org/docs/Phabricator.html>`_. Please include [libcxx] in the subject and
add `cfe-commits` as a subscriber. Also make sure you are subscribed to the
`cfe-commits mailing list <http://lists.llvm.org/mailman/listinfo/cfe-commits>`_.
**Discussion and Questions**
Send discussions and questions to the
`cfe-dev mailing list <http://lists.llvm.org/mailman/listinfo/cfe-dev>`_.
Please include [libcxx] in the subject.
Quick Links
===========
* `LLVM Homepage <http://llvm.org/>`_
* `libc++abi Homepage <http://libcxxabi.llvm.org/>`_
* `LLVM Bugzilla <http://llvm.org/bugs/>`_
* `cfe-commits Mailing List`_
* `cfe-dev Mailing List`_
* `Browse libc++ -- SVN <http://llvm.org/svn/llvm-project/libcxx/trunk/>`_
* `Browse libc++ -- ViewVC <http://llvm.org/viewvc/llvm-project/libcxx/trunk/>`_
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