.. _manage_gcc_abi:

How to manage the GCC >= 5 ABI
==============================

In version 5.1, GCC released libstdc++, which introduced a
`new library ABI <https://gcc.gnu.org/onlinedocs/libstdc++/manual/using_dual_abi.html>`_ that includes new implementations of
``std::string`` and ``std::list``. These changes were necessary to conform to the 2011 C++ standard which forbids Copy-On-Write strings
and requires lists to keep track of their size.

You can choose which ABI to use in your Conan packages by adjusting the ``compiler.libcxx``:

    - **libstdc++**: Old ABI.
    - **libstdc++11**: New ABI.

When Conan creates the default profile the first time it runs, it adjusts the ``compiler.libcxx`` setting to ``libstdc++`` for backwards
compatibility. However, if you are using GCC >= 5 your compiler is likely to be using the new CXX11 ABI by default (libstdc++11).
This can be checked with the following command:

.. code-block:: bash

  $ gcc -v 2>&1 | sed -n 's/.*\(--with-default-libstdcxx-abi=new\).*/\1/p'
  --with-default-libstdcxx-abi=new


If you want Conan to use the new ABI, edit the default profile at ``~/.conan/profiles/default`` adjusting ``compiler.libcxx=libstdc++11``
or override this setting in the profile you are using.

If you are using the :ref:`CMake build helper <cmake_reference>` or the :ref:`AutotoolsBuildEnvironment build helper <autotools_reference>`
Conan will automatically adjust the ``_GLIBCXX_USE_CXX11_ABI`` flag to manage the ABI.