cmake - Header files of shared library not found

Question

I am making a custom library that I want to be installable for users. However, when I try to use my own library in a cmake executable, I get a build error saying that the library headers were not found.

The library CMakeLists.txt:

cmake_minimum_required(VERSION 3.16) project(mylibrary) include(GNUInstallDirs) set(CMAKE_CXX_STANDARD 14) # Register a library - This will created lib[xxx].so add_library(mylibrary SHARED src/library.cpp) configure_file(mylibrary.pc.in mylibrary.pc @ONLY) # List the /include directory target_include_directories(mylibrary PUBLIC $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include> $<INSTALL_INTERFACE:include>) install(TARGETS mylibrary EXPORT mylibraryConfig LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}) export(TARGETS mylibrary FILE "${CMAKE_CURRENT_BINARY_DIR}/mylibraryConfig.cmake") install(EXPORT mylibraryConfig DESTINATION "${CMAKE_INSTALL_LIBDIR}/mylibrary/cmake" NAMESPACE mylibraryConfig::) install( DIRECTORY include DESTINATION ${CMAKE_INSTALL_PREFIX}) install(FILES ${CMAKE_BINARY_DIR}/mylibrary.pc DESTINATION ${CMAKE_INSTALL_DATAROOTDIR}/pkgconfig)

Which I successfully build and install with:

$ cmake .. -DCMAKE_INSTALL_PREFIX=~/libraries/local # Use non-standard destination $ make && make install

The executableCMakeLists.txt:

cmake_minimum_required(VERSION 3.16) project(myexecutable) set(CMAKE_CXX_STANDARD 14) find_package(mylibrary REQUIRED) add_executable(myexecutable src/main.cpp) target_link_libraries(myexecutable PUBLIC mylibrary) target_include_directories(myexecutable PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include)

I can prepare cmake for this project:

$ cmake .. -DCMAKE_PREFIX_PATH=~/libraries/local # Use non-standard location

However, building it fails:

$ make fatal error: mylibrary/library.h: No such file or directory 2 | #include <mylibrary/library.h>

To my understanding the location of the library (binaries and headers) is embedded in the installed package. And through find_package() that information retrieved, so why isn't it working here?

Similar questions:

I largely based my library cmake on: How to create a shared library with cmake?
Same problem but I am already using target_include_directories: Cmake Linking Shared Library: "No such file or directory" when include a header file from library

As far as I know find_package() may not succeed and not even report any message about that: https://stackoverflow.com/questions/2711654.... — bloody
– bloody, Commented Jan 6, 2021 at 16:06
If I run cmake .. (without the DCMAKE_PREFIX_PATH) for the program, I get a neat error like "cannot find package mylibrary". So I'm inclined to think that part works. — Roberto
– Roberto, Commented Jan 6, 2021 at 16:58
As you namespaced your shared library target in the config file you need to reference it with the full name when using find_package, i.e. use mylibraryConfig::mylibrary in the target_link_libraries command. — vre
– vre, Commented Jan 6, 2021 at 23:02
Yup, that's it! I just removed the NAMESPACE bit. If you post this as an answer I'll accept it. Or I'll post it myself later. — Roberto
– Roberto, Commented Jan 7, 2021 at 7:09

Roberto · Accepted Answer · 2021-01-07 09:52:04Z

When a shared library target is namespaced in the config file you need to reference it with the full name in the downstream packages when using find_package, i.e. you need to use

target_link_libraries(myexecutable PUBLIC mylibraryConfig::mylibrary)

Alternatively, remove the namespace from the install by replacing

install(EXPORT mylibraryConfig DESTINATION "${CMAKE_INSTALL_LIBDIR}/mylibrary/cmake" NAMESPACE mylibraryConfig::)

...with:

install(EXPORT mylibraryConfig DESTINATION "${CMAKE_INSTALL_LIBDIR}/mylibrary/cmake")

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