# CMake Variables

## Variables that Provide Information

* `CMAKE_CURRENT_SOURCE_DIR`  The path to the source directory currently being processed.
* `CMAKE_CURRENT_BINARY_DIR`  The path to the binary directory currently being processed.
* `CMAKE_SOURCE_DIR`  The path to the top level of the source tree.
* `CMAKE_BINARY_DIR`  The path to the binary directory currently being processed.
  * for an in-source build, this would be the same as `CMAKE_SOURCE_DIR`
  * for an out-of-source build, this would be at `./build` folder
* `PROJECT_SOURCE_DIR`  Top level source directory for the current project.
* `PROJECT_BINARY_DIR`  Full path to build directory for project.
* `<PROJECT-NAME>_SOURCE_DIR`  Top level source directory for the named project.
* `<PROJECT-NAME>_BINARY_DIR`  Top level binary directory for the named project.
* `PROJECT_VERSION` Value given to the VERSION option of the most recent call to the `project()` command, if any.
* `CMAKE_VERSION`&#x20;
* `CMAKE_COMMAND`  The full path to the cmake executable.
* `CMAKE_GENERATOR`  The generator used to build the project.

```bash
# ~/catkin_ws/src/example_pkg
message(${CMAKE_CURRENT_SOURCE_DIR})
message(${CMAKE_SOURCE_DIR})
message(${PROJECT_SOURCE_DIR})

# ~/catkin_ws/build/example_pkg
message(${CMAKE_CURRENT_BINARY_DIR})
message(${CMAKE_BINARY_DIR})
message(${PROJECT_BINARY_DIR})
```

## Variables that Change Behavior

* `CMAKE_BUILD_TYPE`  Specifies the build type on single-configuration generators.
  * Can be set to `Debug`, `Release`, `RelWithDebInfo`, `MinSizeRel`, ...
* `CMAKE_CONFIGURATION_TYPES` Specifies the available build types on multi-config generators.
* `CMAKE_MODULE_PATH` List of directories to search for CMake modules.
  * Commands like `include()` and `find_package()` search for files in directories listed by this variable before checking the default modules that come with CMake.
* `CMAKE_INSTALL_PREFIX` Install directory used by install.
  * If “make install” is invoked or INSTALL is built, this directory is **prepended** onto all install directories.&#x20;
  * This variable defaults to `/usr/local` on UNIX and `c:/Program Files` on Windows.

#### CMAKE\_XXX\_PATH

By default it is empty, it is intended to be set by the project.

* `CMAKE_PREFIX_PATH`  Path used for searching by FIND\_XXX(), with appropriate suffixes added.
  * a.k.a. `CATKIN_DEVEL_PREFIX` in earlier CMake versions; set to `catkin_ws/devel` for example.
  * It contains the “base” directories, the FIND\_XXX() commands append appropriate subdirectories to the base directories.&#x20;
    * FIND\_PROGRAM() adds `/bin` to each of the directories in the path,&#x20;
    * FIND\_LIBRARY() appends `/lib` to each of the directories, and&#x20;
    * FIND\_FILE() and FIND\_PATH() append `/include`.&#x20;
* `CMAKE_IGNORE_PATH` Path to be ignored by FIND\_XXX() commands.
  * This is useful in cross-compiled environments where some system directories contain incompatible but possibly linkable libraries.&#x20;
* `CMAKE_INCLUDE_PATH` Path used for searching by FIND\_FILE() and FIND\_PATH().
* `CMAKE_LIBRARY_PATH` Path used for searching by FIND\_LIBRARY().
* `CMAKE_PROGRAM_PATH` Path used for searching by FIND\_PROGRAM().

#### CMAKE\_SYSTEM\_XXX\_PATH

By default it contains the standard directories for the current system. It is NOT intended to be modified by the project.

*

```
`CMAKE_SYSTEM_IGNORE_PATH`
```

* `CMAKE_SYSTEM_INCLUDE_PATH`
* `CMAKE_SYSTEM_LIBRARY_PATH`
* `CMAKE_SYSTEM_PREFIX_PATH`
* `CMAKE_SYSTEM_PROGRAM_PATH`

```bash
message("${CMAKE_BUILD_TYPE}")  # add "" to prevent error from empty variable
message("${CMAKE_CONFIGURATION_TYPES}")
message("${CMAKE_MODULE_PATH}")
message("${CMAKE_INSTALL_PREFIX}")
```

## Variables that Describe the System

* `CMAKE_HOST_SYSTEM`
* `CMAKE_SYSTEM_NAME`&#x20;
* `UNIX` or `CMAKE_HOST_UNIX`
* `WIN32` or `CMAKE_HOST_WIN32`
* `MSVC`, `MSVC_VERSION`
* `ENV`: Access environment variables.&#x20;
  * Use the syntax `$ENV{VAR}` to read environment variable VAR.&#x20;
  * See also the `set()` command to set `ENV{VAR}`.

## Variables that Control the Build

* `EXECUTABLE_OUTPUT_PATH`
* `LIBRARY_OUTPUT_PATH`
* `CMAKE_RUNTIME_OUTPUT_DIRECTORY` Where to put all the RUNTIME targets when built.
  * This variable is used to initialize the RUNTIME\_OUTPUT\_DIRECTORY property on all the targets.
  * See that target property for additional information.

## Variables for Languages

* `CMAKE_<LANG>_COMPILER` The full path to the compiler for LANG.
  * `CMAKE_CXX_COMPILER`, `CMAKE_C_COMPILER`
* `CMAKE_<LANG>_FLAGS`  Flags for all build types.
  * `CMAKE_CXX_FLAGS`, `CMAKE_C_FLAGS`
  * `CMAKE_<LANG>_FLAGS_RELEASE`  Flags for Release build type or configuration.
* `CMAKE_CXX_STANDARD` New in version 3.1. Default value for CXX\_STANDARD property of targets.
* `CMAKE_CUDA_STANDARD`New in version 3.8.
  &#x20;Default value for CUDA\_STANDARD property of targets.