Boost.Log with CMake causing undefined reference error

Question

I am trying to use the new Boost.Log library in a project I am working on. The project is built with CMake. I am receiving link errors claiming that the linker has come across undefined references to Boost.Log

Linking CXX executable main
CMakeFiles/main.dir/main.cpp.o: In function `main':
main.cpp:(.text+0x30): undefined reference to `boost::log::v2s_mt_posix::trivial::logger::get()'

I have a simple hello world test that fails with these errors. If I am linking against the Boost.Log libraries what would cause it to generate an undefined reference error?

main.cpp:

#include <boost/log/trivial.hpp>
int main(int argc, char* const argv[]) {
  BOOST_LOG_TRIVIAL(info) << "Hello World";
}

CMakeLists.txt:

CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
FIND_PACKAGE(Boost 1.54 COMPONENTS log REQUIRED)
FIND_PACKAGE(Threads)
INCLUDE_DIRECTORIES(${Boost_INCLUDE_DIR})
ADD_EXECUTABLE(main main.cpp)
TARGET_LINK_LIBRARIES(main ${Boost_LOG_LIBRARY} ${CMAKE_THREAD_LIBS_INIT})

Edit: verbose output from cmake and make

cmake:

-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:476 ] _boost_TEST_VERSIONS = 1.56.0;1.56;1.55.0;1.55;1.54.0;1.54
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:478 ] Boost_USE_MULTITHREADED = TRUE
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:480 ] Boost_USE_STATIC_LIBS = 
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:482 ] Boost_USE_STATIC_RUNTIME = 
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:484 ] Boost_ADDITIONAL_VERSIONS = 
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:486 ] Boost_NO_SYSTEM_PATHS = 
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:538 ] Declared as CMake or Environmental Variables:
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:540 ]   BOOST_ROOT = 
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:542 ]   BOOST_INCLUDEDIR = 
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:544 ]   BOOST_LIBRARYDIR = 
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:546 ] _boost_TEST_VERSIONS = 1.56.0;1.56;1.55.0;1.55;1.54.0;1.54
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:639 ] location of version.hpp: /usr/include/boost/version.hpp
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:663 ] version.hpp reveals boost 1.54.0
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:739 ] guessed _boost_COMPILER = -gcc48
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:749 ] _boost_MULTITHREADED = -mt
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:792 ] _boost_RELEASE_ABI_TAG = -
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:794 ] _boost_DEBUG_ABI_TAG = -d
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:842 ] _boost_LIBRARY_SEARCH_DIRS = /usr/lib64;NO_DEFAULT_PATH
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:930 ] Searching for LOG_LIBRARY_RELEASE: boost_log-gcc48-mt-1_54;boost_log-gcc48-mt;boost_log-mt-1_54;boost_log-mt;boost_log
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:966 ] Searching for LOG_LIBRARY_DEBUG: boost_log-gcc48-mt-d-1_54;boost_log-gcc48-mt-d;boost_log-mt-d-1_54;boost_log-mt-d;boost_log-mt;boost_log
-- [ /usr/share/cmake-2.8/Modules/FindBoost.cmake:1017 ] Boost_FOUND = 1
-- Boost version: 1.54.0
-- Found the following Boost libraries:
--   log
-- Configuring done
-- Generating done
-- Build files have been written to: /home/durrw/boost-log-test/build

make:

/usr/bin/cmake -H/home/durrw/boost-log-test -B/home/durrw/boost-log-test/build --check-build-system CMakeFiles/Makefile.cmake 0
/usr/bin/cmake -E cmake_progress_start /home/durrw/boost-log-test/build/CMakeFiles /home/durrw/boost-log-test/build/CMakeFiles/progress.marks
make -f CMakeFiles/Makefile2 all
make[1]: Entering directory `/home/durrw/boost-log-test/build'
make -f CMakeFiles/main.dir/build.make CMakeFiles/main.dir/depend
make[2]: Entering directory `/home/durrw/boost-log-test/build'
cd /home/durrw/boost-log-test/build && /usr/bin/cmake -E cmake_depends "Unix Makefiles" /home/durrw/boost-log-test /home/durrw/boost-log-test /home/durrw/boost-log-test/build /home/durrw/boost-log-test/build /home/durrw/boost-log-test/build/CMakeFiles/main.dir/DependInfo.cmake --color=
make[2]: Leaving directory `/home/durrw/boost-log-test/build'
make -f CMakeFiles/main.dir/build.make CMakeFiles/main.dir/build
make[2]: Entering directory `/home/durrw/boost-log-test/build'
Linking CXX executable main
/usr/bin/cmake -E cmake_link_script CMakeFiles/main.dir/link.txt --verbose=1
/usr/bin/c++       CMakeFiles/main.dir/main.cpp.o  -o main -rdynamic -lboost_log -lpthread 
CMakeFiles/main.dir/main.cpp.o: In function `main':
main.cpp:(.text+0x39): undefined reference to `boost::log::v2s_mt_posix::trivial::logger::get()'

Solution 1

It looks like it boils down to linking to the shared version of Boost.Log.

There is a bit of detail on the issue in the docs for Boost.Log Your error message mentions the namespace boost::log::v2s_mt_posix and from the docs, this implies the linker is expecting to link to a static version of Boost.Log.

If you want to link to the shared version, it seems you need to define BOOST_LOG_DYN_LINK or BOOST_ALL_DYN_LINK, i.e. in your CMakeLists.txt add:

ADD_DEFINITIONS(-DBOOST_LOG_DYN_LINK)

If you want to link to the static version of Boost.Log, instead you need to add a CMake variable before calling FIND_PACKAGE(Boost ...):

SET(Boost_USE_STATIC_LIBS ON)
FIND_PACKAGE(Boost 1.54 COMPONENTS log REQUIRED)

For further variables which affect how CMake finds Boost, see the docs for FindBoost.

Solution 2

For CMake 3.15 (and some earlier versions) the following appears to be sufficient to build Boost.Log with CMake without the original linker error:

cmake_minimum_required(VERSION 3.15)
project(boost_log_tutorial)

SET(Boost_USE_STATIC_LIBS ON)           # link statically
#ADD_DEFINITIONS(-DBOOST_LOG_DYN_LINK)  # or, link dynamically

find_package(Boost 1.69.0 COMPONENTS log REQUIRED)

add_executable(boost_log_tutorial main.cpp)
target_link_libraries(boost_log_tutorial Boost::log_setup Boost::log)

The key things seem to be linking against Boost:log_setup and Boost::log, and specifying either static or dynamic linking with SET(Boost_USE_STATIC_LIBS ON) or ADD_DEFINITIONS(-DBOOST_LOG_DYN_LINK).

Comments

[Fraser]

If you run cmake . -DBoost_DEBUG=1 and also make VERBOSE=1 you'll get a lot more info about what CMake is doing and what the actual linker command is. Feel free to add the output of these to your question to get more help.

[Bill D]

The debug output was useful, but still doesn't seem to help as it is linking against boost_log

[Fraser]

According to the docs for FindBoost, it looks like either variable is now valid. Also, if that was wrong, wouldn't it result in a compiler error rather than a linker one?

[RobertJMaynard]

Boost_INCLUDE_DIR support was added in CMake 2.8.11, and really can't be used unless you enforce a CMake version check.

[Fraser]

Ah - OK. Still, there'd be a compiler problem with the C++ #include call if that was wrong wouldn't there?

[Bill D]

Needed to add ADD_DEFINITIONS(-DBOOST_LOG_DYN_LINK) to my CMakeLists.txt files. Also I am new to CMake and didn't realize that things are not carried over to CMakeLists.txt files in subfolders. Thought I could add it to the CMakeLists.txt file in the root folder and have it applied to all subfolders. However, I discovered this is not how CMake works.