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"]
          [REQUIRED]
          [NO_DEFAULT_PATH]
          [NO_PACKAGE_ROOT_PATH]
          [NO_CMAKE_PATH]
          [NO_CMAKE_ENVIRONMENT_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. The REQUIRED option stops processing with an error message if nothing is found, otherwise the search will be attempted again the next time find_library is invoked with the same variable.

Options include:

NAMES

Specify one or more possible names for the library.

When using this to specify names with and without a version suffix, we recommend specifying the unversioned name first so that locally-built packages can be found before those provided by distributions.

HINTS, PATHS

Specify directories to search in addition to the default locations. The ENV var sub-option reads paths from a system environment variable.

PATH_SUFFIXES

Specify additional subdirectories to check below each directory location otherwise considered.

DOC

Specify the documentation string for the <VAR> cache entry.

REQUIRED

Stop processing with an error message if nothing is found.

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. If called from within a find module or any other script loaded by a call to find_package(<PackageName>), search prefixes unique to the current package being found. Specifically, look in the <PackageName>_ROOT CMake variable and the <PackageName>_ROOT environment variable. The package root variables are maintained as a stack, so if called from nested find modules or config packages, root paths from the parent’s find module or config package will be searched after paths from the current module or package. In other words, the search order would be <CurrentPackage>_ROOT, ENV{<CurrentPackage>_ROOT}, <ParentPackage>_ROOT, ENV{<ParentPackage>_ROOT}, etc. This can be skipped if NO_PACKAGE_ROOT_PATH is passed or by setting the CMAKE_FIND_USE_PACKAGE_ROOT_PATH to FALSE. See policy CMP0074.

   • <prefix>/lib/<arch> if CMAKE_LIBRARY_ARCHITECTURE is set, and <prefix>/lib for each <prefix> in the <PackageName>_ROOT CMake variable and the <PackageName>_ROOT environment variable if called from within a find module loaded by find_package(<PackageName>)

2. 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 semicolon-separated lists. This can be skipped if NO_CMAKE_PATH is passed or by setting the CMAKE_FIND_USE_CMAKE_PATH to FALSE.

   • <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 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 or by setting the CMAKE_FIND_USE_CMAKE_ENVIRONMENT_PATH to FALSE.

   • <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
4. 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.

5. Search the standard system environment variables. This can be skipped if NO_SYSTEM_ENVIRONMENT_PATH is passed or by setting the CMAKE_FIND_USE_SYSTEM_ENVIRONMENT_PATH to FALSE.

   • The directories in PATH and INCLUDE.
   • On Windows hosts: <prefix>/lib/<arch> if CMAKE_LIBRARY_ARCHITECTURE is set, and <prefix>/lib for each <prefix>/[s]bin in PATH, and <entry>/lib for other entries in PATH.

6. Search cmake variables defined in the Platform files for the current system. This can be skipped if NO_CMAKE_SYSTEM_PATH is passed or by setting the CMAKE_FIND_USE_CMAKE_SYSTEM_PATH to FALSE.

   • <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

   The platform paths that these variables contain are locations that typically include installed software. An example being /usr/local for UNIX based platforms.

7. Search the paths specified by the PATHS option or in the short-hand version of the command. These are typically hard-coded guesses.

On macOS the CMAKE_FIND_FRAMEWORK and CMAKE_FIND_APPBUNDLE variables determine the order of preference between Apple-style and unix-style package components.

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 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_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.

Each library name given to the NAMES option is first considered as a library file name and then considered with platform-specific prefixes (e.g. lib) and suffixes (e.g. .so). Therefore one may specify library file names such as libfoo.a directly. This can be used to locate static libraries on UNIX-like systems.

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 CMAKE_FIND_LIBRARY_CUSTOM_LIB_SUFFIX variable is set all search paths will be tested as normal, with the suffix appended, and with all matches of lib/ replaced with lib${CMAKE_FIND_LIBRARY_CUSTOM_LIB_SUFFIX}/. This variable overrides the FIND_LIBRARY_USE_LIB32_PATHS, FIND_LIBRARY_USE_LIBX32_PATHS, and FIND_LIBRARY_USE_LIB64_PATHS global properties.

If the FIND_LIBRARY_USE_LIB32_PATHS global property is set all search paths will be tested as normal, with 32/ appended, and with all matches of lib/ replaced with lib32/. 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.

If the FIND_LIBRARY_USE_LIBX32_PATHS global property is set all search paths will be tested as normal, with x32/ appended, and with all matches of lib/ replaced with libx32/. 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.

If the FIND_LIBRARY_USE_LIB64_PATHS global property 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.