# find_package

Load settings for an external project.

    find_package(<package> [version] [EXACT] [QUIET] [MODULE]
                 [REQUIRED] [[COMPONENTS] [components...]]
                 [OPTIONAL_COMPONENTS components...]
                 [NO_POLICY_SCOPE])

Finds and loads settings from an external project. `<package>_FOUND` will be set to indicate whether the package was found. When the package is found package-specific information is provided through variables and Imported Targets documented by the package itself. The `QUIET` option disables messages if the package cannot be found. The `MODULE` option disables the second signature documented below. The `REQUIRED` option stops processing with an error message if the package cannot be found.

A package-specific list of required components may be listed after the `COMPONENTS` option (or after the `REQUIRED` option if present). Additional optional components may be listed after `OPTIONAL_COMPONENTS`. Available components and their influence on whether a package is considered to be found are defined by the target package.

The `[version]` argument requests a version with which the package found should be compatible (format is `major[.minor[.patch[.tweak]]]`). The `EXACT` option requests that the version be matched exactly. If no `[version]` and/or component list is given to a recursive invocation inside a find-module, the corresponding arguments are forwarded automatically from the outer call (including the `EXACT` flag for `[version]`). Version support is currently provided only on a package-by-package basis (details below).

User code should generally look for packages using the above simple signature. The remainder of this command documentation specifies the full command signature and details of the search process. Project maintainers wishing to provide a package to be found by this command are encouraged to read on.

The command has two modes by which it searches for packages: “Module” mode and “Config” mode. Module mode is available when the command is invoked with the above reduced signature. CMake searches for a file called `Find<package>.cmake` in the `CMAKE_MODULE_PATH` followed by the CMake installation. If the file is found, it is read and processed by CMake. It is responsible for finding the package, checking the version, and producing any needed messages. Many find-modules provide limited or no support for versioning; check the module documentation. If no module is found and the `MODULE` option is not given the command proceeds to Config mode.

The complete Config mode command signature is:

    find_package(<package> [version] [EXACT] [QUIET]
                 [REQUIRED] [[COMPONENTS] [components...]]
                 [CONFIG|NO_MODULE]
                 [NO_POLICY_SCOPE]
                 [NAMES name1 [name2 ...]]
                 [CONFIGS config1 [config2 ...]]
                 [HINTS path1 [path2 ... ]]
                 [PATHS path1 [path2 ... ]]
                 [PATH_SUFFIXES suffix1 [suffix2 ...]]
                 [NO_DEFAULT_PATH]
                 [NO_CMAKE_PATH]
                 [NO_CMAKE_ENVIRONMENT_PATH]
                 [NO_SYSTEM_ENVIRONMENT_PATH]
                 [NO_CMAKE_PACKAGE_REGISTRY]
                 [NO_CMAKE_BUILDS_PATH] # Deprecated; does nothing.
                 [NO_CMAKE_SYSTEM_PATH]
                 [NO_CMAKE_SYSTEM_PACKAGE_REGISTRY]
                 [CMAKE_FIND_ROOT_PATH_BOTH |
                  ONLY_CMAKE_FIND_ROOT_PATH |
                  NO_CMAKE_FIND_ROOT_PATH])

The `CONFIG` option may be used to skip Module mode explicitly and switch to Config mode. It is synonymous to using `NO_MODULE`. Config mode is also implied by use of options not specified in the reduced signature.

Config mode attempts to locate a configuration file provided by the package to be found. A cache entry called `<package>_DIR` is created to hold the directory containing the file. By default the command searches for a package with the name `<package>`. If the `NAMES` option is given the names following it are used instead of `<package>`. The command searches for a file called `<name>Config.cmake` or `<lower-case-name>-config.cmake` for each name specified. A replacement set of possible configuration file names may be given using the `CONFIGS` option. The search procedure is specified below. Once found, the configuration file is read and processed by CMake. Since the file is provided by the package it already knows the location of package contents. The full path to the configuration file is stored in the cmake variable `<package>_CONFIG`.

All configuration files which have been considered by CMake while searching for an installation of the package with an appropriate version are stored in the cmake variable `<package>_CONSIDERED_CONFIGS`, the associated versions in `<package>_CONSIDERED_VERSIONS`.

If the package configuration file cannot be found CMake will generate an error describing the problem unless the `QUIET` argument is specified. If `REQUIRED` is specified and the package is not found a fatal error is generated and the configure step stops executing. If `<package>_DIR` has been set to a directory not containing a configuration file CMake will ignore it and search from scratch.

When the `[version]` argument is given Config mode will only find a version of the package that claims compatibility with the requested version (format is `major[.minor[.patch[.tweak]]]`). If the `EXACT` option is given only a version of the package claiming an exact match of the requested version may be found. CMake does not establish any convention for the meaning of version numbers. Package version numbers are checked by “version” files provided by the packages themselves. For a candidate package configuration file `<config-file>.cmake` the corresponding version file is located next to it and named either `<config-file>-version.cmake` or `<config-file>Version.cmake`. If no such version file is available then the configuration file is assumed to not be compatible with any requested version. A basic version file containing generic version matching code can be created using the `CMakePackageConfigHelpers` module. When a version file is found it is loaded to check the requested version number. The version file is loaded in a nested scope in which the following variables have been defined:

`PACKAGE_FIND_NAME`
  the `<package>` name
`PACKAGE_FIND_VERSION`
  full requested version string
`PACKAGE_FIND_VERSION_MAJOR`
  major version if requested, else 0
`PACKAGE_FIND_VERSION_MINOR`
  minor version if requested, else 0
`PACKAGE_FIND_VERSION_PATCH`
  patch version if requested, else 0
`PACKAGE_FIND_VERSION_TWEAK`
  tweak version if requested, else 0
`PACKAGE_FIND_VERSION_COUNT`
  number of version components, 0 to 4

The version file checks whether it satisfies the requested version and sets these variables:

`PACKAGE_VERSION`
  full provided version string
`PACKAGE_VERSION_EXACT`
  true if version is exact match
`PACKAGE_VERSION_COMPATIBLE`
  true if version is compatible
`PACKAGE_VERSION_UNSUITABLE`
  true if unsuitable as any version

These variables are checked by the `find_package` command to determine whether the configuration file provides an acceptable version. They are not available after the find_package call returns. If the version is acceptable the following variables are set:

`<package>_VERSION`
  full provided version string
`<package>_VERSION_MAJOR`
  major version if provided, else 0
`<package>_VERSION_MINOR`
  minor version if provided, else 0
`<package>_VERSION_PATCH`
  patch version if provided, else 0
`<package>_VERSION_TWEAK`
  tweak version if provided, else 0
`<package>_VERSION_COUNT`
  number of version components, 0 to 4

and the corresponding package configuration file is loaded. When multiple package configuration files are available whose version files claim compatibility with the version requested it is unspecified which one is chosen: unless the variable `CMAKE_FIND_PACKAGE_SORT_ORDER` is set no attempt is made to choose a highest or closest version number.

To control the order in which `find_package` checks for compatibiliy use the two variables `CMAKE_FIND_PACKAGE_SORT_ORDER` and `CMAKE_FIND_PACKAGE_SORT_DIRECTION`. For instance in order to select the highest version one can set:

    SET(CMAKE_FIND_PACKAGE_SORT_ORDER NATURAL)
    SET(CMAKE_FIND_PACKAGE_SORT_DIRECTION DEC)

before calling `find_package`.

Config mode provides an elaborate interface and search procedure. Much of the interface is provided for completeness and for use internally by find-modules loaded by Module mode. Most user code should simply call:

    find_package(<package> [major[.minor]] [EXACT] [REQUIRED|QUIET])

in order to find a package. Package maintainers providing CMake package configuration files are encouraged to name and install them such that the procedure outlined below will find them without requiring use of additional options.

CMake constructs a set of possible installation prefixes for the package. Under each prefix several directories are searched for a configuration file. The tables below show the directories searched. Each entry is meant for installation trees following Windows (W), UNIX (U), or Apple (A) conventions:

    <prefix>/                                                       (W)
    <prefix>/(cmake|CMake)/                                         (W)
    <prefix>/<name>*/                                               (W)
    <prefix>/<name>*/(cmake|CMake)/                                 (W)
    <prefix>/(lib/<arch>|lib|share)/cmake/<name>*/                  (U)
    <prefix>/(lib/<arch>|lib|share)/<name>*/                        (U)
    <prefix>/(lib/<arch>|lib|share)/<name>*/(cmake|CMake)/          (U)
    <prefix>/<name>*/(lib/<arch>|lib|share)/cmake/<name>*/          (W/U)
    <prefix>/<name>*/(lib/<arch>|lib|share)/<name>*/                (W/U)
    <prefix>/<name>*/(lib/<arch>|lib|share)/<name>*/(cmake|CMake)/  (W/U)

On systems supporting OS X Frameworks and Application Bundles the following directories are searched for frameworks or bundles containing a configuration file:

    <prefix>/<name>.framework/Resources/                    (A)
    <prefix>/<name>.framework/Resources/CMake/              (A)
    <prefix>/<name>.framework/Versions/*/Resources/         (A)
    <prefix>/<name>.framework/Versions/*/Resources/CMake/   (A)
    <prefix>/<name>.app/Contents/Resources/                 (A)
    <prefix>/<name>.app/Contents/Resources/CMake/           (A)

In all cases the `<name>` is treated as case-insensitive and corresponds to any of the names specified (`<package>` or names given by `NAMES`). Paths with `lib/<arch>` are enabled if the `CMAKE_LIBRARY_ARCHITECTURE` variable is set. If `PATH_SUFFIXES` is specified the suffixes are appended to each (W) or (U) directory entry one-by-one.

This set of directories is intended to work in cooperation with projects that provide configuration files in their installation trees. Directories above marked with (W) are intended for installations on Windows where the prefix may point at the top of an application’s installation directory. Those marked with (U) are intended for installations on UNIX platforms where the prefix is shared by multiple packages. This is merely a convention, so all (W) and (U) directories are still searched on all platforms. Directories marked with (A) are intended for installations on Apple platforms. The `CMAKE_FIND_FRAMEWORK` and `CMAKE_FIND_APPBUNDLE` variables determine the order of preference.

The set of installation prefixes is constructed using the following steps. If `NO_DEFAULT_PATH` is specified all `NO_*` options are enabled.

1. Search paths specified in cmake-specific cache variables. These are intended to be used on the command line with a `-DVAR=value`. The values are interpreted as ;-lists. This can be skipped if `NO_CMAKE_PATH` is passed:

       CMAKE_PREFIX_PATH
       CMAKE_FRAMEWORK_PATH
       CMAKE_APPBUNDLE_PATH

2. Search paths specified in cmake-specific environment variables. These are intended to be set in the user’s shell configuration, and therefore use the host’s native path separator (`;` on Windows and `:` on UNIX). This can be skipped if `NO_CMAKE_ENVIRONMENT_PATH` is passed:

       <package>_DIR
       CMAKE_PREFIX_PATH
       CMAKE_FRAMEWORK_PATH
       CMAKE_APPBUNDLE_PATH

3. Search paths specified by the `HINTS` option. These should be paths computed by system introspection, such as a hint provided by the location of another item already found. Hard-coded guesses should be specified with the `PATHS` option.

4. Search the standard system environment variables. This can be skipped if `NO_SYSTEM_ENVIRONMENT_PATH` is passed. Path entries ending in `/bin` or `/sbin` are automatically converted to their parent directories:

       PATH

5. Search paths stored in the CMake User Package Registry. This can be skipped if `NO_CMAKE_PACKAGE_REGISTRY` is passed or by setting the `CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY` to `TRUE`. See the `cmake-packages(7)` manual for details on the user package registry.

6. Search cmake variables defined in the Platform files for the current system. This can be skipped if `NO_CMAKE_SYSTEM_PATH` is passed:

       CMAKE_SYSTEM_PREFIX_PATH
       CMAKE_SYSTEM_FRAMEWORK_PATH
       CMAKE_SYSTEM_APPBUNDLE_PATH

7. Search paths stored in the CMake System Package Registry. This can be skipped if `NO_CMAKE_SYSTEM_PACKAGE_REGISTRY` is passed or by setting the `CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY` to `TRUE`. See the `cmake-packages(7)` manual for details on the system package registry.

8. Search paths specified by the `PATHS` option. These are typically hard-coded guesses.

The CMake variable `CMAKE_FIND_ROOT_PATH` specifies one or more directories to be prepended to all other search directories. This effectively “re-roots” the entire search under given locations. Paths which are descendants of the `CMAKE_STAGING_PREFIX` are excluded from this re-rooting, because that variable is always a path on the host system. By default the `CMAKE_FIND_ROOT_PATH` is empty.

The `CMAKE_SYSROOT` variable can also be used to specify exactly one directory to use as a prefix. Setting `CMAKE_SYSROOT` also has other effects. See the documentation for that variable for more.

These variables are especially useful when cross-compiling to point to the root directory of the target environment and CMake will search there too. By default at first the directories listed in `CMAKE_FIND_ROOT_PATH` are searched, then the `CMAKE_SYSROOT` directory is searched, and then the non-rooted directories will be searched. The default behavior can be adjusted by setting `CMAKE_FIND_ROOT_PATH_MODE_PACKAGE`. This behavior can be manually overridden on a per-call basis using options:

`CMAKE_FIND_ROOT_PATH_BOTH`
  Search in the order described above.
`NO_CMAKE_FIND_ROOT_PATH`
  Do not use the `CMAKE_FIND_ROOT_PATH` variable.
`ONLY_CMAKE_FIND_ROOT_PATH`
  Search only the re-rooted directories and directories below `CMAKE_STAGING_PREFIX`.

The default search order is designed to be most-specific to least-specific for common use cases. Projects may override the order by simply calling the command multiple times and using the `NO_*` options:

    find_package (<package> PATHS paths... NO_DEFAULT_PATH)
    find_package (<package>)

Once one of the calls succeeds the result variable will be set and stored in the cache so that no call will search again.

Every non-REQUIRED `find_package` call can be disabled by setting the `CMAKE_DISABLE_FIND_PACKAGE_<PackageName>` variable to `TRUE`.

When loading a find module or package configuration file `find_package` defines variables to provide information about the call arguments (and restores their original state before returning):

`CMAKE_FIND_PACKAGE_NAME`
  the `<package>` name which is searched for
`<package>_FIND_REQUIRED`
  true if `REQUIRED` option was given
`<package>_FIND_QUIETLY`
  true if `QUIET` option was given
`<package>_FIND_VERSION`
  full requested version string
`<package>_FIND_VERSION_MAJOR`
  major version if requested, else 0
`<package>_FIND_VERSION_MINOR`
  minor version if requested, else 0
`<package>_FIND_VERSION_PATCH`
  patch version if requested, else 0
`<package>_FIND_VERSION_TWEAK`
  tweak version if requested, else 0
`<package>_FIND_VERSION_COUNT`
  number of version components, 0 to 4
`<package>_FIND_VERSION_EXACT`
  true if `EXACT` option was given
`<package>_FIND_COMPONENTS`
  list of requested components
`<package>_FIND_REQUIRED_<c>`
  true if component `<c>` is required, false if component `<c>` is optional

In Module mode the loaded find module is responsible to honor the request detailed by these variables; see the find module for details. In Config mode `find_package` handles `REQUIRED`, `QUIET`, and `[version]` options automatically but leaves it to the package configuration file to handle components in a way that makes sense for the package. The package configuration file may set `<package>_FOUND` to false to tell `find_package` that component requirements are not satisfied.

See the `cmake_policy()` command documentation for discussion of the `NO_POLICY_SCOPE` option.