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# find_library

A short-hand signature is:

    find_library (<VAR> name1 [path1 path2 ...])

The general signature is:

    find_library (
              <VAR>
              name | NAMES name1 [name2 ...] [NAMES_PER_DIR]
              [HINTS path1 [path2 ... ENV var]]
              [PATHS path1 [path2 ... ENV var]]
              [PATH_SUFFIXES suffix1 [suffix2 ...]]
              [DOC "cache documentation string"]
              [NO_DEFAULT_PATH]
              [NO_CMAKE_ENVIRONMENT_PATH]
              [NO_CMAKE_PATH]
              [NO_SYSTEM_ENVIRONMENT_PATH]
              [NO_CMAKE_SYSTEM_PATH]
              [CMAKE_FIND_ROOT_PATH_BOTH |
               ONLY_CMAKE_FIND_ROOT_PATH |
               NO_CMAKE_FIND_ROOT_PATH]
             )

This command is used to find a library. A cache entry named by `<VAR>` is created to store the result of this command. If the library is found the result is stored in the variable and the search will not be repeated unless the variable is cleared. If nothing is found, the result will be `<VAR>-NOTFOUND`, and the search will be attempted again the next time find_library is invoked with the same variable. The name of the library that is searched for is specified by the names listed after the NAMES argument. Additional search locations can be specified after the PATHS argument. If ENV var is found in the HINTS or PATHS section the environment variable var will be read and converted from a system environment variable to a cmake style list of paths. For example ENV PATH would be a way to list the system path variable. The argument after DOC will be used for the documentation string in the cache. PATH_SUFFIXES specifies additional subdirectories to check below each search path.

If NO_DEFAULT_PATH is specified, then no additional paths are added to the search. If NO_DEFAULT_PATH is not specified, the search process is as follows:

1. Search paths specified in cmake-specific cache variables. These are intended to be used on the command line with a -DVAR=value. This can be skipped if NO_CMAKE_PATH is passed.
   - <prefix>/lib/<arch> if CMAKE_LIBRARY_ARCHITECTURE is set, and <prefix>/lib for each <prefix> in CMAKE_PREFIX_PATH
   - CMAKE_LIBRARY_PATH
   - CMAKE_FRAMEWORK_PATH
2. Search paths specified in cmake-specific environment variables. These are intended to be set in the user’s shell configuration. This can be skipped if NO_CMAKE_ENVIRONMENT_PATH is passed.
   - <prefix>/lib/<arch> if CMAKE_LIBRARY_ARCHITECTURE is set, and <prefix>/lib for each <prefix> in CMAKE_PREFIX_PATH
   - CMAKE_LIBRARY_PATH
   - CMAKE_FRAMEWORK_PATH
3. Search the 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 an argument.
   - PATH and LIB
5. Search cmake variables defined in the Platform files for the current system. This can be skipped if NO_CMAKE_SYSTEM_PATH is passed.
   - <prefix>/lib/<arch> if CMAKE_LIBRARY_ARCHITECTURE is set, and <prefix>/lib for each <prefix> in CMAKE_SYSTEM_PREFIX_PATH
   - CMAKE_SYSTEM_LIBRARY_PATH
   - CMAKE_SYSTEM_FRAMEWORK_PATH
6. Search the paths specified by the PATHS option or in the short-hand version of the command. These are typically hard-coded guesses.

On Darwin or systems supporting OS X Frameworks, the cmake variable CMAKE_FIND_FRAMEWORK can be set to empty or one of the following:

- FIRST: Try to find frameworks before standard libraries or headers. This is the default on Darwin.
- LAST: Try to find frameworks after standard libraries or headers.
- ONLY: Only try to find frameworks.
- NEVER: Never try to find frameworks.

On Darwin or systems supporting OS X Application Bundles, the cmake variable CMAKE_FIND_APPBUNDLE can be set to empty or one of the following:

- FIRST: Try to find application bundles before standard programs. This is the default on Darwin.
- LAST: Try to find application bundles after standard programs.
- ONLY: Only try to find application bundles.
- NEVER: Never try to find application bundles.

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_LIBRARY`. This behavior can be manually overridden on a per-call basis. By using CMAKE_FIND_ROOT_PATH_BOTH the search order will be as described above. If NO_CMAKE_FIND_ROOT_PATH is used then `CMAKE_FIND_ROOT_PATH` will not be used. If ONLY_CMAKE_FIND_ROOT_PATH is used then only the re-rooted directories and directories below `CMAKE_STAGING_PREFIX` will be searched.

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_library (<VAR> NAMES name PATHS paths... NO_DEFAULT_PATH)
    find_library (<VAR> NAMES name)

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

When more than one value is given to the NAMES option this command by default will consider one name at a time and search every directory for it. The NAMES_PER_DIR option tells this command to consider one directory at a time and search for all names in it.

If the library found is a framework, then VAR will be set to the full path to the framework <fullPath>/A.framework. When a full path to a framework is used as a library, CMake will use a -framework A, and a -F<fullPath> to link the framework to the target.

If the global property FIND_LIBRARY_USE_LIB64_PATHS is set all search paths will be tested as normal, with “64/” appended, and with all matches of “lib/” replaced with “lib64/”. This property is automatically set for the platforms that are known to need it if at least one of the languages supported by the PROJECT command is enabled.

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