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< font size = 5 > CMake < / font > is an extensible, open-source system that
manages the build process in an operating system and compiler independent
manner. Unlike many cross-platform systems, CMake is designed to be used
in conjunction with the native build environment. Simple configuration
files placed in each source directory (called CMakeLists.txt files) are
used to generate standard build files (e.g., makefiles on Unix and
projects/workspaces in Windows MSVC) which are used in the usual
way. CMake can compile source code, create libraries, generate wrappers,
and build executables in arbitrary combinations. CMake supports in-place
and out-of-place builds, and can therefore support multiple builds from a
single source tree. CMake also supports static and dynamic library
builds. Another nice feature of CMake is that it generates a cache file
that is designed to be used with a graphical editor. For example, when
CMake runs, it locates include files, libraries, and executable, and may
encounter optional build directives. This information is gathered into
the cache, which may be changed by the user prior to the generation of
the native build files. (The following figure is the CMake cache GUI in
the Windows MSVC environment.)
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< P >
CMake is designed to support complex directory hierarchies and
applications dependent on several libraries. For example, CMake supports
projects consisting of multiple toolkits (i.e., libraries), where each
toolkit might contain several directories, and the application depends on
the toolkits plus additional code. CMake can also handle situations where
executables must be built in order to generate code that is then compiled
and linked into a final application. Because CMake is open source, and has
a simple, extensible design, CMake can be extended as necessary to support
new features.
< P >
Using CMake is simple. The build process is controlled by creating one or
more CMakeLists.txt files in each directory (including subdirectories)
that make up a project. Each CMakeLists.txt consists of one or more
commands. Each command has the form COMMAND (args...) where COMMAND is
the name of the command, and args is a white-space separated list of
arguments. CMake provides many pre-defined commands, but if you need to,
you can add your own commands. In addition, the advanced user can add
other makefile generators for a particular compiler/OS combination.
(While Unix and MSVC++ is supported currently, other developers are
adding other compiler/OS support.) You may wish to study the
< a href = "/CMake/HTML/Examples.html" > examples< / a > page to see more
details.
< h3 > A Summary Of Features< / h3 >
CMake has several powerful features. These include:
< ul >
< li > Supports complex, large build environments. CMake has been
proven in several large projects.
< li > Generates native build files (e.g., makefiles on Unix;
workspaces/projects on MS Visual C++). Therefore standard
tools can be used on any platform/compiler configuration.
< li > Has powerful commands include the ability to locate
include files, libraries, executables; include external
CMake files that encapsulate standard functionality;
interfaces to testing systems; supports recursive
directory traversal with variable inheritance; can run
external programs; supports conditional builds; supports
regular expression expansion; and so on.
< li > Supports in-place and out-of-place builds. Multiple
compilation trees are possible from a single source tree.
< li > Can be easily extended to add new features.
< li > CMake is open source.
< li > CMake operates with a cache designed to be interfaced with
a graphical editor. The cache provides optional interaction
to conditionally control the build process.
< / ul >
< h3 > The Origins of CMake< / h3 > CMake was created in response to the need
for a powerful, cross-platform build environment for the Insight
Segmentation and Registration Toolkit (ITK) funded by NLM as part of the
Visible Human Project. It grew out of an earlier system called
< b > pcmaker< / b > created by Ken Martin and other developers to support the
< a href = "http://public.kitware.com/vtk.html" > Visualization Toolkit
(VTK)< / a > open source 3D graphics and visualization system. To create
CMake, Bill Hoffman at Kitware incorporated some key ideas from pcmaker,
with the thought to adopt some of the functionality of the Unix
< b > configure< / b > tool. The initial CMake implementation was mid-2000,
with acclerated development occuring in early 2001. Many improvements
were due to the influences of other developers incorporating CMake into
their own systems. For example, the
< a href = "http://www.robots.ox.ac.uk/~vxl/" > VXL< / a > software community
adopted CMake as their build environment, contributing many essential
features. Brad King added several features in order to support the CABLE
automated wrapping environment and
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< a href = "http://public.kitware.com/GCC_XML" > GCC-XML< / a > , and
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GE Corporate R& D required support of their testing infrastructure
(the < a href = "http://public.kitware.com/Insight/Testing/HTML/TestingResults/Dashboard/MostRecentResults-Nightly/Dashboard.html" > quality dashboard< / a > ). Other
features were added by Ken Martin to support the transition of VTK's
build environment to CMake, and to support ParaView, a parallel
visualization system to support the
< a href = "http://www.acl.lanl.gov/" > Advanced Computing Lab< / a > at Los Alamos
National Laboratory.
< h3 > How Do I Learn CMake?< / h3 > CMake is a young and rapidly growing
system. It has already seen extensive use in very large software systems
such as VTK, VXL, and ITK, and is therefore, quite
stable. Unfortuneately, the pace of development has outstripped the pace
of documentation. As a result, the best way to learn about CMake is to
study existing CMake installations, and to rely on the CMake mailing
list. There is some existing documentation, but until later in 2001 the
documentation should be treated with caution. Please go to the
< a href = "/CMake/HTML/Documentation.html" > documentation< / a > for more
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information. Also, see the < a href = "/CMake/HTML/Examples.html" > example< / a >
found here.
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