CMake Useful Variables

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CMake uses and defines many variables, which can be used in CMakeLists.txt files.

NOTE: As of CMake 2.6.0 many of these variables have been officially documented in TXT and HTML files released with CMake. You may still see some useful variables here that haven't yet been documented in the official documentation, although the number of these diminishes with every release. This page, in either case, is more of a distilled list of some of the more important variables. The official documentation is home of the authoritative guide to all CMake variables, commands, and properties.

Locations

CMAKE_BINARY_DIR
if you are building in-source, this is the same as CMAKE_SOURCE_DIR, otherwise this is the top level directory of your build tree
CMAKE_COMMAND
this is the complete path of the cmake which runs currently (e.g. /usr/local/bin/cmake). Note that if you have custom commands that invoke cmake -E, it is very important to use CMAKE_COMMAND as the CMake executable, because CMake might not be on the system PATH.
CMAKE_CURRENT_BINARY_DIR
if you are building in-source, this is the same as CMAKE_CURRENT_SOURCE_DIR, otherwise this is the directory where the compiled or generated files from the current CMakeLists.txt will go to.
CMAKE_CURRENT_SOURCE_DIR
this is the directory where the currently processed CMakeLists.txt is located in
CMAKE_CURRENT_LIST_FILE
this is the full path to the listfile currently being processed.
CMAKE_CURRENT_LIST_DIR
(since 2.8.3) this is the directory of the listfile currently being processed.
CMAKE_CURRENT_LIST_LINE
this is linenumber where the variable is used.
CMAKE_FILES_DIRECTORY
the directory within the current binary directory that contains all the CMake generated files. Typically evaluates to "/CMakeFiles". Note the leading slash for the directory. Typically used with the current binary directory, i.e. ${CMAKE_CURRENT_BINARY_DIR}${CMAKE_FILES_DIRECTORY}
CMAKE_MODULE_PATH
tell CMake to search first in directories listed in CMAKE_MODULE_PATH when you use FIND_PACKAGE() or INCLUDE()
SET(CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/MyCMakeScripts)
FIND_PACKAGE(HelloWorld)
CMAKE_ROOT
this is the CMake installation directory
CMAKE_SOURCE_DIR
this is the directory which contains the top-level CMakeLists.txt, i.e. the top level source directory
PROJECT_NAME
the name of the project set by PROJECT() command.
CMAKE_PROJECT_NAME
the name of the first project set by the PROJECT() command, i.e. the top level project.
PROJECT_BINARY_DIR
contains the full path to the top level directory of your build tree
PROJECT_SOURCE_DIR
contains the full path to the root of your project source directory, i.e. to the nearest directory where CMakeLists.txt contains the PROJECT() command

Environment Variables

These are environment variables which effect cmake behaviour.

CMAKE_INCLUDE_PATH
This is used when searching for include files e.g. using the FIND_PATH() command. If you have headers in non-standard locations, it may be useful to set this variable to this directory (e.g. /sw/include on Mac OS X). If you need several directories, separate them by the platform specific separators (e.g. ":" on UNIX)
CMAKE_LIBRARY_PATH
This is used when searching for libraries e.g. using the FIND_LIBRARY() command. If you have libraries in non-standard locations, it may be useful to set this variable to this directory (e.g. /sw/lib on Mac OS X). If you need several directories, separate them by the platform specific separators (e.g. ":" on UNIX)
CMAKE_PREFIX_PATH
(since CMake 2.6.0) This is used when searching for include files, binaries, or libraries using either the FIND_PACKAGE(), FIND_PATH(), FIND_PROGRAM(), or FIND_LIBRARY() commands. For each path in the CMAKE_PREFIX_PATH list, CMake will check "PATH/include" and "PATH" when FIND_PATH() is called, "PATH/bin" and "PATH" when FIND_PROGRAM() is called, and "PATH/lib" and "PATH" when FIND_LIBRARY() is called. See the documentation for FIND_PACKAGE(), FIND_LIBRARY(), FIND_PATH(), and FIND_PROGRAM() for more details.
CMAKE_INSTALL_ALWAYS
If set during installation CMake will install all files whether they have changed or not. The default when this is not set is to install only files that have changed since the previous installation. In both cases all files are reported to indicate CMake knows they are up to date in the installed location.
$ENV{name}
This is not an environment variable , but this is how you can access environment variables from cmake files. It returns the content of the environment variable with the given name (e.g. $ENV{PROGRAMFILES})
DESTDIR
If this environment variable is set it will be prefixed to CMAKE_INSTALL_PREFIX in places where it is used to access files during installation. This allows the files to be installed in an intermediate directory tree without changing the final installation path name. Since the value of CMAKE_INSTALL_PREFIX may be included in installed files it is important to use DESTDIR rather than changing CMAKE_INSTALL_PREFIX when it is necessary to install to a intermediate staging directory.

System & Compiler Information

CMAKE_MAJOR_VERSION
major version number for CMake, e.g. the "2" in CMake 2.4.3
CMAKE_MINOR_VERSION
minor version number for CMake, e.g. the "4" in CMake 2.4.3
CMAKE_PATCH_VERSION
patch version number for CMake, e.g. the "3" in CMake 2.4.3
CMAKE_TWEAK_VERSION
tweak version number for CMake, e.g. the "1" in CMake X.X.X.1. Releases use tweak < 20000000 and development versions use the date format CCYYMMDD for the tweak level.
CMAKE_VERSION
The version number combined, eg. 2.8.4.20110222-ged5ba for a Nightly build. or 2.8.4 for a Release build.
CMAKE_GENERATOR
the generator specified on the commandline.
BORLAND
is TRUE on Windows when using a Borland compiler
WATCOM
is TRUE on Windows when using the Open Watcom compiler
MSVC, MSVC_IDE, MSVC60, MSVC70, MSVC71, MSVC80, CMAKE_COMPILER_2005, MSVC90, MSVC10 (Visual Studio 2010)
Microsoft compiler
CMAKE_C_COMPILER_ID
one of "Clang", "GNU", "Intel", or "MSVC". This works even if a compiler wrapper like ccache is used.
CMAKE_CXX_COMPILER_ID
one of "Clang", "GNU", "Intel", or "MSVC". This works even if a compiler wrapper like ccache is used.

Various Options

CMAKE_SKIP_RULE_DEPENDENCY
set this to true if you don't want to rebuild the object files if the rules have changed, but not the actual source files or headers (e.g. if you changed the some compiler switches)
CMAKE_SKIP_INSTALL_ALL_DEPENDENCY
since CMake 2.1 the install rule depends on all, i.e. everything will be built before installing. If you don't like this, set this one to true.
CMAKE_INCLUDE_CURRENT_DIR
automatically add CMAKE_CURRENT_SOURCE_DIR and CMAKE_CURRENT_BINARY_DIR to the include directories in every processed CMakeLists.txt. It behaves as if you had used INCLUDE_DIRECTORIES in every CMakeLists.txt file or your project. The added directory paths are relative to the being-processed CMakeLists.txt, which is different in each directory. (See this thread for more details).
CMAKE_INCLUDE_DIRECTORIES_PROJECT_BEFORE
order the include directories so that directories which are in the source or build tree always come before directories outside the project.
CMAKE_VERBOSE_MAKEFILE
set this to true if you are using makefiles and want to see the full compile and link commands instead of only the shortened ones
CMAKE_SUPPRESS_REGENERATION
this will cause CMake to not put in the rules that re-run CMake. This might be useful if you want to use the generated build files on another machine.
CMAKE_COLOR_MAKEFILE
create Makefiles with colored output (defaults to on)
CMAKE_SKIP_PREPROCESSED_SOURCE_RULES
(since 2.4.4) if set to TRUE, the generated Makefiles will not contain rules for creating preprocessed files (foo.i)
CMAKE_SKIP_ASSEMBLY_SOURCE_RULES
(since 2.4.4) if set to TRUE, the generated Makefiles will not contain rules for creating compiled, but not yet assembled files (foo.s)

Compilers and Tools

BUILD_SHARED_LIBS
if this is set to ON, then all libraries are built as shared libraries by default.
SET(BUILD_SHARED_LIBS ON)
CMAKE_BUILD_TYPE
A variable which controls the type of build when using a single-configuration generator like the Makefile generator. CMake will create by default the following variables when using a single-configuration generator:
  • None (CMAKE_C_FLAGS or CMAKE_CXX_FLAGS used)
  • Debug (CMAKE_C_FLAGS_DEBUG or CMAKE_CXX_FLAGS_DEBUG)
  • Release (CMAKE_C_FLAGS_RELEASE or CMAKE_CXX_FLAGS_RELEASE)
  • RelWithDebInfo (CMAKE_C_FLAGS_RELWITHDEBINFO or CMAKE_CXX_FLAGS_RELWITHDEBINFO
  • MinSizeRel (CMAKE_C_FLAGS_MINSIZEREL or CMAKE_CXX_FLAGS_MINSIZEREL)

You can use these default compilation flags (or modify them) by setting the CMAKE_BUILD_TYPE variable at configuration time from within the "ccmake" GUI. Note! The default values for these flags change with different compilers. If CMake does not know your compiler, the contents will be empty.

If you are using the Makefile generator, you can create your own build type like this:
SET(CMAKE_BUILD_TYPE distribution)
SET(CMAKE_CXX_FLAGS_DISTRIBUTION "-O3")
SET(CMAKE_C_FLAGS_DISTRIBUTION "-O3")

Note that CMAKE_BUILD_TYPE is not initialized with a readable value at configuration time. This is because the user is free to select a build type at build time. Use CMAKE_CFG_INTDIR if you need a variable that evaluates to the correct build time directory.

CMAKE_CONFIGURATION_TYPES
When using a multi-configuration generator, such as the one for Visual Studio, this variable contains a list of the available configurations.
CMAKE_C_COMPILER
the compiler used for C files. Normally it is detected and set during the CMake run, but you can override it at configuration time. Note! It can not be changed after the first cmake or ccmake run. Although the gui allows to enter an alternative, it will be ignored in the next 'configure' run. Use for example:
CC=gcc-3.3 CXX=g++-3.3 cmake
to set the compiler. (You can also set CMAKE_C_COMPILER_INIT, before any PROJECT() or ENABLE_LANGUAGE() command.) Any other way (like writing make CC=gcc-3.3 CXX=g++-3.3) will not work. When using distcc or similar tools, you need to write:
CC="distcc gcc-3.3" CXX="distcc g++-3.3" cmake
However, this will empty all your CMAKE_..._FLAGS_... above.
CMAKE_C_FLAGS
the compiler flags for compiling C sources. Note you can also specify switches with ADD_COMPILE_OPTIONS().
CMAKE_C_FLAGS_<CONFIG>
compiler flags for a specific build configuration. Replace "<CONFIG>" in the name with a specific build configuration name.
CMAKE_C_OUTPUT_EXTENSION
what C object files end in. Typically .o or .obj.
CMAKE_CFG_INTDIR
meta-variable! Please note that this is an important variable, since on multi-configuration generators it will be generated into dynamically switched content based on the configuration that the user currently selected within the generated build environment. Indicates the name of the current configuration (~ directory) for the project. May be used for any purpose which needs per-configuration-dynamic switching of strings, not just OutputDir configuration. For multi-configuration generators (e.g. MSVC) the resulting strings are typically some of "Debug", "Release", "RelWithDebInfo", or "MinSizeRel". For other compiler generators (single-configuration ones) it is typically ".", as they don't use MSVC-style configuration directories.
CMAKE_CXX_COMPILER
the compiler used for C++ files. Normally it is detected and set during the CMake run, but you can override it at configuration time. Note! It can not be changed after the first cmake or ccmake run. See CMAKE_C_COMPILER above.
CMAKE_CXX_FLAGS
the compiler flags for compiling C++ sources. Note you can also specify switches with ADD_COMPILE_OPTIONS().
CMAKE_CXX_FLAGS_<CONFIG>
compiler flags for a specific configuration for C++ sources. Replace "<CONFIG>" in the name with a specific build configuration name.
CMAKE_SHARED_LINKER_FLAGS
additional compiler flags for building shared libraries, e.g.:

set(CMAKE_SHARED_LINKER_FLAGS "-Wl,--no-undefined")
On Unix systems, this will make linker report any unresolved symbols from object files (which is quite typical when you compile many targets in CMake projects, but do not bother with linking target dependencies in proper order). On mac, the flag is -Wl,-undefined-error.

Prefixes, Suffixes (Postfixes), and Extensions

CMAKE_EXECUTABLE_SUFFIX
Suffix of executables on the target platform.
CMAKE_FIND_LIBRARY_PREFIXES
List of possible library prefixes used by find_library(). "lib" on UNIX systems.
CMAKE_FIND_LIBRARY_SUFFIXES
List of possible library suffixes used by find_library(). ".a;.so" on UNIX systems. Note that it's possible to use this to control whether find_package() modules find shared or static libraries.
CMAKE_<SHARED|STATIC>_LIBRARY_PREFIX
Prefix for shared or static libraries on this platform. Read-only.
CMAKE_<SHARED|STATIC>_LIBRARY_SUFFIX
Suffix for shared or static libraries on this platform. Read-only.
CMAKE_<config>_POSTFIX
Adds a custom "postfix" to static and shared libraries when in a certain build type. Example: Setting CMAKE_BUILD_TYPE=DEBUG and CMAKE_DEBUG_POSTFIX="_d" would turn mylib.lib into mylib_d.lib.

Build rules

Build rules are defined in CMakeCInformation.cmake and CMakeCXXInformation.cmake. Essentially, they're a template for the command CMake uses to invoke the compiler or linker to do different tasks.

Rules for C++ sources:

CMAKE_CXX_CREATE_SHARED_LIBRARY
CMAKE_CXX_CREATE_SHARED_MODULE
CMAKE_CXX_CREATE_STATIC_LIBRARY
CMAKE_CXX_COMPILE_OBJECT
CMAKE_CXX_LINK_EXECUTABLE

and the equivalents for C sources:

CMAKE_C_CREATE_SHARED_LIBRARY
CMAKE_C_CREATE_SHARED_MODULE
CMAKE_C_CREATE_STATIC_LIBRARY
CMAKE_C_COMPILE_OBJECT
CMAKE_C_LINK_EXECUTABLE

You can override the variables manually, e.g. replacing some flags in the linker command, but you can't change the value of the variables in sharp braces. Usually you don't have to change these rules, only in rare cases. You should only do this if you know what you are doing and there is no other way.

Expansion Rules

From examining the source code the following style names exist:

ASSEMBLY_SOURCE
FLAGS
LANGUAGE_COMPILE_FLAGS
LINK_FLAGS
LINK_LIBRARIES
OBJECT
OBJECTS
OBJECTS_QUOTED
OBJECT_DIR
PREPROCESSED_SOURCE
SOURCE
TARGET
TARGET_BASE
TARGET_IMPLIB
TARGET_INSTALLNAME_DIR
TARGET_PDB
TARGET_QUOTED
TARGET_SONAME
TARGET_VERSION_MAJOR
TARGET_VERSION_MINOR

Please note you can set these properties globally using SET or LIST, or for a single target using SET_TARGET_PROPERTIES.

Variables not listed here

CMake has many more variables than are listed above. Documenting all of them is an ongoing project. We need everyone's help with this. If you know of a CMake variable that is not listed here, please edit the wiki and add it. Don't worry about whether you have a precise description for it. This is a wiki, and other people can provide a better description as time goes on.

How does one find out about additional variables? The CMake mailing list is probably the best resource. Some things can be learned from inspecting the CMake source code. Many - but not all of them - are also listed by this Dashboard script for extracting variables. The output of this script is rather raw, but it is a good starting point for finding more variables.

When a CMake dashboard is run, a "SystemInformation test" is usually run as well. Among other things, it lists the names and values of all of the CMake variables that are in use when the test is run. The script looks at the SystemInformation test output, and uses regular expressions to find the start and end of the "AllVariables.txt" section. It prints the results out in the form of XML.

Logging code

This code may be placed in a CMakelists.txt file to create status messages that log a number of the variables documented above. It is not a complete list, however. The variables are not auto-generated from the wiki, it is just sample code. Add whatever variables you are interested in.

  1. Sample code for logging useful variables.



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