CMake's find_library(): Why It Might Not Find Your Library
CMake's find_library() function is a powerful tool for locating external libraries in your project. However, it's not a magic bullet and sometimes you might find that it doesn't discover the library you're looking for.
This article explores the common reasons why find_library() might fail to find a library and provides solutions to overcome these obstacles.
Scenario: You're trying to use an external library in your project, but find_library() returns empty. You've checked your CMakeLists.txt and the library appears to be installed in the expected location, but CMake just won't find it.
Example Code:
find_library(Boost_LIBRARIES Boost)
if (Boost_LIBRARIES)
message("Boost library found!")
else()
message("Boost library NOT found!")
endif()
In this example, the code searches for the "Boost" library and prints a message indicating whether it was found. But, if you run CMake and Boost_LIBRARIES is empty, you might be wondering why.
Common Reasons and Solutions:
-
Incorrect Library Name: The most common reason for
find_library()failing is an incorrect library name. Make sure the name you pass tofind_library()matches the actual library file name. Some libraries might have different names for different platforms, so check the documentation. -
Incorrect Search Paths: CMake uses default search paths for libraries, but these paths might not include your library's installation directory. You can explicitly set search paths using the
CMAKE_LIBRARY_PATHvariable:set(CMAKE_LIBRARY_PATH "${CMAKE_LIBRARY_PATH}/path/to/your/library") find_library(Boost_LIBRARIES Boost) -
Library Installation Errors: Sometimes, even though you think the library is installed, there might be issues with its installation. Double-check your installation steps and ensure the library is correctly installed and its headers and libraries are accessible.
-
Missing Find Module: CMake relies on "Find Modules" to locate libraries. For popular libraries like Boost, find modules are usually included with CMake. However, for less common libraries, you might need to create a custom find module. You can find instructions and examples on the CMake documentation website [https://cmake.org/cmake/help/v3.16/manual/cmake-modules.7.html].
-
Case Sensitivity: On some operating systems (like Linux and macOS), library names are case-sensitive. Make sure the name you're using in
find_library()matches the case of the actual library file name.
Additional Tips:
- Verbose Output: Use
cmake -DCMAKE_VERBOSE_MAKEFILE=ON ..to enable verbose output. This will provide detailed information about the search paths and other actions CMake takes, which can be helpful in debugging. - Custom Search Paths: If your library isn't in standard locations, use the
find_path()function to locate the library's header files and then usefind_library()with the directory found byfind_path(). - Environment Variables: Some libraries rely on environment variables to configure their installation paths. Make sure the relevant environment variables are set correctly before running CMake.
Conclusion:
While find_library() is a powerful tool, it sometimes requires careful configuration to locate external libraries successfully. By understanding the common reasons for failure and applying the suggested solutions, you can avoid these issues and smoothly integrate external libraries into your CMake projects. Remember to check the library's documentation for specific installation and configuration requirements.
