CMake/Help/policy/CMP0018.rst

CMP0018
-------

Ignore ``CMAKE_SHARED_LIBRARY_<Lang>_FLAGS`` variable.

CMake 2.8.8 and lower compiled sources in ``SHARED`` and ``MODULE`` libraries
using the value of the undocumented ``CMAKE_SHARED_LIBRARY_<Lang>_FLAGS``
platform variable.  The variable contained platform-specific flags
needed to compile objects for shared libraries.  Typically it included
a flag such as ``-fPIC`` for position independent code but also included
other flags needed on certain platforms.  CMake 2.8.9 and higher
prefer instead to use the :prop_tgt:`POSITION_INDEPENDENT_CODE` target
property to determine what targets should be position independent, and new
undocumented platform variables to select flags while ignoring
``CMAKE_SHARED_LIBRARY_<Lang>_FLAGS`` completely.

The default for either approach produces identical compilation flags,
but if a project modifies ``CMAKE_SHARED_LIBRARY_<Lang>_FLAGS`` from its
original value this policy determines which approach to use.

The ``OLD`` behavior for this policy is to ignore the
:prop_tgt:`POSITION_INDEPENDENT_CODE` property for all targets and use the
modified value of ``CMAKE_SHARED_LIBRARY_<Lang>_FLAGS`` for ``SHARED`` and
``MODULE`` libraries.

The ``NEW`` behavior for this policy is to ignore
``CMAKE_SHARED_LIBRARY_<Lang>_FLAGS`` whether it is modified or not and
honor the :prop_tgt:`POSITION_INDEPENDENT_CODE` target property.

This policy was introduced in CMake version 2.8.9.  CMake version
|release| warns when the policy is not set and uses ``OLD`` behavior.  Use
the :command:`cmake_policy` command to set it to ``OLD`` or ``NEW``
explicitly.

.. include:: DEPRECATED.txt