cmake version 2.6-patch 4
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Introduction
cmake-policies - Reference of CMake policies.
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Description
The "cmake" executable is the CMake command-line interface. It may be used
to configure projects in scripts. Project configuration settings may be
specified on the command line with the -D option. The -i option will cause
cmake to interactively prompt for such settings.
CMake is a cross-platform build system generator. Projects specify their
build process with platform-independent CMake listfiles included in each
directory of a source tree with the name CMakeLists.txt. Users build a
project by using CMake to generate a build system for a native tool on their
platform.
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Policies
CMP0000
A minimum required CMake version must be specified.
CMake requires that projects specify the version of CMake to which
they have been written. This policy has been put in place so users
trying to build the project may be told when they need to update their
CMake. Specifying a version also helps the project build with CMake
versions newer than that specified. Use the cmake_minimum_required
command at the top of your main CMakeLists.txt file:
cmake_minimum_required(VERSION <major>.<minor>)
where "<major>.<minor>" is the version of CMake you want to support
(such as "2.6"). The command will ensure that at least the given
version of CMake is running and help newer versions be compatible with
the project. See documentation of cmake_minimum_required for details.
Note that the command invocation must appear in the CMakeLists.txt
file itself; a call in an included file is not sufficient. However,
the cmake_policy command may be called to set policy CMP0000 to OLD or
NEW behavior explicitly. The OLD behavior is to silently ignore the
missing invocation. The NEW behavior is to issue an error instead of
a warning. An included file may set CMP0000 explicitly to affect how
this policy is enforced for the main CMakeLists.txt file.
This policy was introduced in CMake version 2.6.0.
CMP0001
CMAKE_BACKWARDS_COMPATIBILITY should no longer be used.
The OLD behavior is to check CMAKE_BACKWARDS_COMPATIBILITY and present
it to the user. The NEW behavior is to ignore
CMAKE_BACKWARDS_COMPATIBILITY completely.
In CMake 2.4 and below the variable CMAKE_BACKWARDS_COMPATIBILITY was
used to request compatibility with earlier versions of CMake. In
CMake 2.6 and above all compatibility issues are handled by policies
and the cmake_policy command. However, CMake must still check
CMAKE_BACKWARDS_COMPATIBILITY for projects written for CMake 2.4 and
below.
This policy was introduced in CMake version 2.6.0. CMake version 2.6
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy command to set it to OLD or NEW explicitly.
CMP0002
Logical target names must be globally unique.
Targets names created with add_executable, add_library, or
add_custom_target are logical build target names. Logical target
names must be globally unique because:
- Unique names may be referenced unambiguously both in CMake
code and on make tool command lines.
- Logical names are used by Xcode and VS IDE generators
to produce meaningful project names for the targets.
The logical name of executable and library targets does not have to
correspond to the physical file names built. Consider using the
OUTPUT_NAME target property to create two targets with the same
physical name while keeping logical names distinct. Custom targets
must simply have globally unique names (unless one uses the global
property ALLOW_DUPLICATE_CUSTOM_TARGETS with a Makefiles generator).
This policy was introduced in CMake version 2.6.0. CMake version 2.6
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy command to set it to OLD or NEW explicitly.
CMP0003
Libraries linked via full path no longer produce linker search paths.
This policy affects how libraries whose full paths are NOT known are
found at link time, but was created due to a change in how CMake deals
with libraries whose full paths are known. Consider the code
target_link_libraries(myexe /path/to/libA.so)
CMake 2.4 and below implemented linking to libraries whose full paths
are known by splitting them on the link line into separate components
consisting of the linker search path and the library name. The
example code might have produced something like
... -L/path/to -lA ...
in order to link to library A. An analysis was performed to order
multiple link directories such that the linker would find library A in
the desired location, but there are cases in which this does not work.
CMake versions 2.6 and above use the more reliable approach of passing
the full path to libraries directly to the linker in most cases. The
example code now produces something like
... /path/to/libA.so ....
Unfortunately this change can break code like
target_link_libraries(myexe /path/to/libA.so B)
where "B" is meant to find "/path/to/libB.so". This code is wrong
because the user is asking the linker to find library B but has not
provided a linker search path (which may be added with the
link_directories command). However, with the old linking
implementation the code would work accidentally because the linker
search path added for library A allowed library B to be found.
In order to support projects depending on linker search paths added by
linking to libraries with known full paths, the OLD behavior for this
policy will add the linker search paths even though they are not
needed for their own libraries. When this policy is set to OLD, CMake
will produce a link line such as
... -L/path/to /path/to/libA.so -lB ...
which will allow library B to be found as it was previously. When
this policy is set to NEW, CMake will produce a link line such as
... /path/to/libA.so -lB ...
which more accurately matches what the project specified.
The setting for this policy used when generating the link line is that
in effect when the target is created by an add_executable or
add_library command. For the example described above, the code
cmake_policy(SET CMP0003 OLD) # or cmake_policy(VERSION 2.4)
add_executable(myexe myexe.c)
target_link_libraries(myexe /path/to/libA.so B)
will work and suppress the warning for this policy. It may also be
updated to work with the corrected linking approach:
cmake_policy(SET CMP0003 NEW) # or cmake_policy(VERSION 2.6)
link_directories(/path/to) # needed to find library B
add_executable(myexe myexe.c)
target_link_libraries(myexe /path/to/libA.so B)
Even better, library B may be specified with a full path:
add_executable(myexe myexe.c)
target_link_libraries(myexe /path/to/libA.so /path/to/libB.so)
When all items on the link line have known paths CMake does not check
this policy so it has no effect.
Note that the warning for this policy will be issued for at most one
target. This avoids flooding users with messages for every target
when setting the policy once will probably fix all targets.
This policy was introduced in CMake version 2.6.0. CMake version 2.6
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy command to set it to OLD or NEW explicitly.
CMP0004
Libraries linked may not have leading or trailing whitespace.
CMake versions 2.4 and below silently removed leading and trailing
whitespace from libraries linked with code like
target_link_libraries(myexe " A ")
This could lead to subtle errors in user projects.
The OLD behavior for this policy is to silently remove leading and
trailing whitespace. The NEW behavior for this policy is to diagnose
the existence of such whitespace as an error. The setting for this
policy used when checking the library names is that in effect when the
target is created by an add_executable or add_library command.
This policy was introduced in CMake version 2.6.0. CMake version 2.6
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy command to set it to OLD or NEW explicitly.
CMP0005
Preprocessor definition values are now escaped automatically.
This policy determines whether or not CMake should generate escaped
preprocessor definition values added via add_definitions. CMake
versions 2.4 and below assumed that only trivial values would be given
for macros in add_definitions calls. It did not attempt to escape
non-trivial values such as string literals in generated build rules.
CMake versions 2.6 and above support escaping of most values, but
cannot assume the user has not added escapes already in an attempt to
work around limitations in earlier versions.
The OLD behavior for this policy is to place definition values given
to add_definitions directly in the generated build rules without
attempting to escape anything. The NEW behavior for this policy is to
generate correct escapes for all native build tools automatically.
See documentation of the COMPILE_DEFINITIONS target property for
limitations of the escaping implementation.
This policy was introduced in CMake version 2.6.0. CMake version 2.6
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy command to set it to OLD or NEW explicitly.
CMP0006
Installing MACOSX_BUNDLE targets requires a BUNDLE DESTINATION.
This policy determines whether the install(TARGETS) command must be
given a BUNDLE DESTINATION when asked to install a target with the
MACOSX_BUNDLE property set. CMake 2.4 and below did not distinguish
application bundles from normal executables when installing targets.
CMake 2.6 provides a BUNDLE option to the install(TARGETS) command
that specifies rules specific to application bundles on the Mac.
Projects should use this option when installing a target with the
MACOSX_BUNDLE property set.
The OLD behavior for this policy is to fall back to the RUNTIME
DESTINATION if a BUNDLE DESTINATION is not given. The NEW behavior
for this policy is to produce an error if a bundle target is installed
without a BUNDLE DESTINATION.
This policy was introduced in CMake version 2.6.0. CMake version 2.6
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy command to set it to OLD or NEW explicitly.
CMP0007
list command no longer ignores empty elements.
This policy determines whether the list command will ignore empty
elements in the list. CMake 2.4 and below list commands ignored all
empty elements in the list. For example, a;b;;c would have length 3
and not 4. The OLD behavior for this policy is to ignore empty list
elements. The NEW behavior for this policy is to correctly count
empty elements in a list.
This policy was introduced in CMake version 2.6.0. CMake version 2.6
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy command to set it to OLD or NEW explicitly.
CMP0008
Libraries linked by full-path must have a valid library file name.
In CMake 2.4 and below it is possible to write code like
target_link_libraries(myexe /full/path/to/somelib)
where "somelib" is supposed to be a valid library file name such as
"libsomelib.a" or "somelib.lib". For Makefile generators this
produces an error at build time because the dependency on the full
path cannot be found. For VS IDE and Xcode generators this used to
work by accident because CMake would always split off the library
directory and ask the linker to search for the library by name
(-lsomelib or somelib.lib). Despite the failure with Makefiles, some
projects have code like this and build only with VS and/or Xcode.
This version of CMake prefers to pass the full path directly to the
native build tool, which will fail in this case because it does not
name a valid library file.
This policy determines what to do with full paths that do not appear
to name a valid library file. The OLD behavior for this policy is to
split the library name from the path and ask the linker to search for
it. The NEW behavior for this policy is to trust the given path and
pass it directly to the native build tool unchanged.
This policy was introduced in CMake version 2.6.1. CMake version 2.6
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy command to set it to OLD or NEW explicitly.
CMP0009
FILE GLOB_RECURSE calls should not follow symlinks by default.
In CMake 2.6.1 and below, FILE GLOB_RECURSE calls would follow through
symlinks, sometimes coming up with unexpectedly large result sets
because of symlinks to top level directories that contain hundreds of
thousands of files.
This policy determines whether or not to follow symlinks encountered
during a FILE GLOB_RECURSE call. The OLD behavior for this policy is
to follow the symlinks. The NEW behavior for this policy is not to
follow the symlinks by default, but only if FOLLOW_SYMLINKS is given
as an additional argument to the FILE command.
This policy was introduced in CMake version 2.6.2. CMake version 2.6
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy command to set it to OLD or NEW explicitly.
CMP0010
Bad variable reference syntax is an error.
In CMake 2.6.2 and below, incorrect variable reference syntax such as
a missing close-brace ("${FOO") was reported but did not stop
processing of CMake code. This policy determines whether a bad
variable reference is an error. The OLD behavior for this policy is
to warn about the error, leave the string untouched, and continue.
The NEW behavior for this policy is to report an error.
This policy was introduced in CMake version 2.6.3. CMake version 2.6
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy command to set it to OLD or NEW explicitly.
CMP0011
Included scripts do automatic cmake_policy PUSH and POP.
In CMake 2.6.2 and below, CMake Policy settings in scripts loaded by
the include() and find_package() commands would affect the includer.
Explicit invocations of cmake_policy(PUSH) and cmake_policy(POP) were
required to isolate policy changes and protect the includer. While
some scripts intend to affect the policies of their includer, most do
not. In CMake 2.6.3 and above, include() and find_package() by
default PUSH and POP an entry on the policy stack around an included
script, but provide a NO_POLICY_SCOPE option to disable it. This
policy determines whether or not to imply NO_POLICY_SCOPE for
compatibility. The OLD behavior for this policy is to imply
NO_POLICY_SCOPE for include() and find_package() commands. The NEW
behavior for this policy is to allow the commands to do their default
cmake_policy PUSH and POP.
This policy was introduced in CMake version 2.6.3. CMake version 2.6
warns when the policy is not set and uses OLD behavior. Use the
cmake_policy command to set it to OLD or NEW explicitly.
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Copyright
Copyright (c) 2002 Kitware, Inc., Insight Consortium. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions are met:
Redistributions of source code must retain the above copyright notice, this
list of conditions and the following disclaimer.
Redistributions in binary form must reproduce the above copyright notice,
this list of conditions and the following disclaimer in the documentation
and/or other materials provided with the distribution.
The names of Kitware, Inc., the Insight Consortium, or the names of any
consortium members, or of any contributors, may not be used to endorse or
promote products derived from this software without specific prior written
permission.
Modified source versions must be plainly marked as such, and must not be
misrepresented as being the original software.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDER AND CONTRIBUTORS ``AS IS''
AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE FOR
ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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See Also
.B ccmake(1), cpack(1), ctest(1), cmakecommands(1), cmakecompat(1),
cmakemodules(1), cmakeprops(1), cmakevars(1)
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