Conan + CMake + C++ : Linking against Boost.Log static library fails – Ubuntu

I am trying to set up a basic Boost.Logging demo project, with Conan and CMake.

I’m using Conan 1.53.0 and CMake 3.22.1, with gcc-11.3.0, on Ubuntu 22.04.1.

First, I use Conan to bring in Boost 1.81, thus my conanfile.txt:

[requires]
boost/1.81.0

[options]
boost:shared=False

[generators]
CMakeDeps
CMakeToolchain

I am using the Conan "toolchain" developer flow, as recommended by the docs. That is why I’m using CMakeToolchain, and that requires CMakeDeps.

For my CMakeLists.txt I have the following:

cmake_minimum_required(VERSION 3.22)
project(log_demo)

set(CMAKE_CXX_STANDARD 17)

set(Boost_USE_STATIC_LIBS ON)
find_package(Boost 1.81.0 COMPONENTS log_setup log REQUIRED)

add_executable(log_demo log_demo.cpp)
target_link_libraries(log_demo PRIVATE Boost::log_setup Boost::log)

Note that I have selected static libs, which matches with the [options] / boost:shared=False selection in conanfile.txt.

Finally, my actual code, log_demo.cpp, is trivial:

#include <boost/log/core.hpp>
#include <boost/log/trivial.hpp>
#include <boost/log/expressions.hpp>

int main()
{
    BOOST_LOG_TRIVIAL(debug) << "This is debug";
    return 0;
}

I invoke Conan to get Boost with:

$ mkdir build && cd build
$ conan install ..
Configuration:
[settings]
arch=x86_64
arch_build=x86_64
build_type=Release
compiler=gcc
compiler.libcxx=libstdc++11
compiler.version=11
os=Linux
os_build=Linux
[options]
[build_requires]
[env]

conanfile.txt: Installing package
Requirements
    boost/1.81.0 from 'conancenter' - Cache
    bzip2/1.0.8 from 'conancenter' - Cache
    libbacktrace/cci.20210118 from 'conancenter' - Cache
    zlib/1.2.13 from 'conancenter' - Cache
Packages
    boost/1.81.0:dc8aedd23a0f0a773a5fcdcfe1ae3e89c4205978 - Cache
    bzip2/1.0.8:c32092bf4d4bb47cf962af898e02823f499b017e - Cache
    libbacktrace/cci.20210118:dfbe50feef7f3c6223a476cd5aeadb687084a646 - Cache
    zlib/1.2.13:dfbe50feef7f3c6223a476cd5aeadb687084a646 - Cache

...

This generated, amongst other files, conan_toolchain.cmake in this build directory.

Now I can invoke CMake to configure the build:

$ cmake -DCMAKE_TOOLCHAIN_FILE=conan_toolchain.cmake -DCMAKE_BUILD_TYPE=Debug ..
-- Using Conan toolchain: /home/david/cpp/log_demo/build/conan_toolchain.cmake
-- The C compiler identification is GNU 11.3.0
-- The CXX compiler identification is GNU 11.3.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/bin/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Conan: Component target declared 'Boost::diagnostic_definitions'
-- Conan: Component target declared 'Boost::disable_autolinking'
-- Conan: Component target declared 'Boost::dynamic_linking'
-- Conan: Component target declared 'Boost::headers'
-- Conan: Component target declared 'Boost::boost'
-- Conan: Component target declared 'boost::_libboost'
-- Conan: Component target declared 'Boost::atomic'
-- Conan: Component target declared 'Boost::container'
-- Conan: Component target declared 'Boost::context'
-- Conan: Component target declared 'Boost::date_time'
-- Conan: Component target declared 'Boost::exception'
-- Conan: Component target declared 'Boost::math'
-- Conan: Component target declared 'Boost::math_c99'
-- Conan: Component target declared 'Boost::math_c99f'
-- Conan: Component target declared 'Boost::math_c99l'
-- Conan: Component target declared 'Boost::math_tr1'
-- Conan: Component target declared 'Boost::math_tr1f'
-- Conan: Component target declared 'Boost::math_tr1l'
-- Conan: Component target declared 'Boost::program_options'
-- Conan: Component target declared 'Boost::regex'
-- Conan: Component target declared 'Boost::serialization'
-- Conan: Component target declared 'Boost::stacktrace'
-- Conan: Component target declared 'Boost::stacktrace_addr2line'
-- Conan: Component target declared 'Boost::stacktrace_backtrace'
-- Conan: Component target declared 'Boost::stacktrace_basic'
-- Conan: Component target declared 'Boost::stacktrace_noop'
-- Conan: Component target declared 'Boost::system'
-- Conan: Component target declared 'Boost::test'
-- Conan: Component target declared 'Boost::test_exec_monitor'
-- Conan: Component target declared 'Boost::url'
-- Conan: Component target declared 'Boost::wserialization'
-- Conan: Component target declared 'Boost::chrono'
-- Conan: Component target declared 'Boost::coroutine'
-- Conan: Component target declared 'Boost::filesystem'
-- Conan: Component target declared 'Boost::json'
-- Conan: Component target declared 'Boost::nowide'
-- Conan: Component target declared 'Boost::prg_exec_monitor'
-- Conan: Component target declared 'Boost::random'
-- Conan: Component target declared 'Boost::thread'
-- Conan: Component target declared 'Boost::timer'
-- Conan: Component target declared 'Boost::type_erasure'
-- Conan: Component target declared 'Boost::unit_test_framework'
-- Conan: Component target declared 'Boost::wave'
-- Conan: Component target declared 'Boost::contract'
-- Conan: Component target declared 'Boost::fiber'
-- Conan: Component target declared 'Boost::fiber_numa'
-- Conan: Component target declared 'Boost::graph'
-- Conan: Component target declared 'Boost::iostreams'
-- Conan: Component target declared 'Boost::locale'
-- Conan: Component target declared 'Boost::log'
-- Conan: Component target declared 'Boost::log_setup'
-- Conan: Target declared 'boost::boost'
-- Conan: Target declared 'BZip2::BZip2'
-- Conan: Including build module from '/home/david/.conan/data/bzip2/1.0.8/_/_/package/c32092bf4d4bb47cf962af898e02823f499b017e/lib/cmake/conan-official-bzip2-variables.cmake'
-- Conan: Target declared 'ZLIB::ZLIB'
-- Conan: Target declared 'libbacktrace::libbacktrace'
-- Configuring done
-- Generating done
-- Build files have been written to: /home/david/cpp/log_demo/build

And where things go wrong is with linking against Boost.Log:

$ cmake --build .
[ 50%] Building CXX object CMakeFiles/log_demo.dir/log_demo.cpp.o
[100%] Linking CXX executable log_demo
/usr/bin/ld: CMakeFiles/log_demo.dir/log_demo.cpp.o: in function `main':
/home/david/cpp/log_demo/log_demo.cpp:7: undefined reference to `boost::log::v2s_mt_posix::trivial::logger::get()'
/usr/bin/ld: /home/david/cpp/log_demo/log_demo.cpp:7: undefined reference to `boost::log::v2s_mt_posix::trivial::logger::get()'
/usr/bin/ld: CMakeFiles/log_demo.dir/log_demo.cpp.o: in function `boost::log::v2s_mt_posix::record::reset()':
/usr/include/boost/log/core/record.hpp:157: undefined reference to `boost::log::v2s_mt_posix::record_view::public_data::destroy(boost::log::v2s_mt_posix::record_view::public_data const*)'
/usr/bin/ld: CMakeFiles/log_demo.dir/log_demo.cpp.o: in function `boost::log::v2s_mt_posix::record boost::log::v2s_mt_posix::sources::basic_composite_logger<char, boost::log::v2s_mt_posix::sources::severity_logger_mt<boost::log::v2s_mt_posix::trivial::severity_level>, boost::log::v2s_mt_posix::sources::multi_thread_model<boost::log::v2s_mt_posix::aux::light_rw_mutex>, boost::log::v2s_mt_posix::sources::features<boost::log::v2s_mt_posix::sources::severity<boost::log::v2s_mt_posix::trivial::severity_level> > >::open_record<boost::parameter::aux::tagged_argument_list_of_1<boost::parameter::aux::tagged_argument<boost::log::v2s_mt_posix::keywords::tag::severity, boost::log::v2s_mt_posix::trivial::severity_level const> > >(boost::parameter::aux::tagged_argument_list_of_1<boost::parameter::aux::tagged_argument<boost::log::v2s_mt_posix::keywords::tag::severity, boost::log::v2s_mt_posix::trivial::severity_level const> > const&)':
/usr/include/boost/log/sources/basic_logger.hpp:463: undefined reference to `boost::log::v2s_mt_posix::core::get_logging_enabled() const'
/usr/bin/ld: CMakeFiles/log_demo.dir/log_demo.cpp.o: in function `boost::log::v2s_mt_posix::aux::record_pump<boost::log::v2s_mt_posix::sources::severity_logger_mt<boost::log::v2s_mt_posix::trivial::severity_level> >::record_pump(boost::log::v2s_mt_posix::sources::severity_logger_mt<boost::log::v2s_mt_posix::trivial::severity_level>&, boost::log::v2s_mt_posix::record&)':
/usr/include/boost/log/sources/record_ostream.hpp:508: undefined reference to `boost::log::v2s_mt_posix::aux::stream_provider<char>::allocate_compound(boost::log::v2s_mt_posix::record&)'
/usr/bin/ld: CMakeFiles/log_demo.dir/log_demo.cpp.o: in function `boost::log::v2s_mt_posix::aux::record_pump<boost::log::v2s_mt_posix::sources::severity_logger_mt<boost::log::v2s_mt_posix::trivial::severity_level> >::auto_release::~auto_release()':
/usr/include/boost/log/sources/record_ostream.hpp:493: undefined reference to `boost::log::v2s_mt_posix::aux::stream_provider<char>::release_compound(boost::log::v2s_mt_posix::aux::stream_provider<char>::stream_compound*)'
/usr/bin/ld: CMakeFiles/log_demo.dir/log_demo.cpp.o: in function `boost::log::v2s_mt_posix::sources::aux::severity_level<boost::log::v2s_mt_posix::trivial::severity_level>::set_value(boost::log::v2s_mt_posix::trivial::severity_level)':
/usr/include/boost/log/sources/severity_feature.hpp:137: undefined reference to `boost::log::v2s_mt_posix::sources::aux::get_severity_level()'
/usr/bin/ld: CMakeFiles/log_demo.dir/log_demo.cpp.o: in function `boost::log::v2s_mt_posix::record boost::log::v2s_mt_posix::sources::basic_logger<char, boost::log::v2s_mt_posix::sources::severity_logger_mt<boost::log::v2s_mt_posix::trivial::severity_level>, boost::log::v2s_mt_posix::sources::multi_thread_model<boost::log::v2s_mt_posix::aux::light_rw_mutex> >::open_record_unlocked<boost::parameter::aux::tagged_argument_list_of_1<boost::parameter::aux::tagged_argument<boost::log::v2s_mt_posix::keywords::tag::severity, boost::log::v2s_mt_posix::trivial::severity_level const> > >(boost::parameter::aux::tagged_argument_list_of_1<boost::parameter::aux::tagged_argument<boost::log::v2s_mt_posix::keywords::tag::severity, boost::log::v2s_mt_posix::trivial::severity_level const> > const&)':
/usr/include/boost/log/sources/basic_logger.hpp:263: undefined reference to `boost::log::v2s_mt_posix::core::open_record(boost::log::v2s_mt_posix::attribute_set const&)'
/usr/bin/ld: CMakeFiles/log_demo.dir/log_demo.cpp.o: in function `boost::log::v2s_mt_posix::core::push_record(boost::log::v2s_mt_posix::record&&)':
/usr/include/boost/log/core/core.hpp:308: undefined reference to `boost::log::v2s_mt_posix::core::push_record_move(boost::log::v2s_mt_posix::record&)'
collect2: error: ld returned 1 exit status
gmake[2]: *** [CMakeFiles/log_demo.dir/build.make:97: log_demo] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:83: CMakeFiles/log_demo.dir/all] Error 2
gmake: *** [Makefile:91: all] Error 2

This linker error – undefined reference to 'boost::log::v2s_mt_posix::trivial::logger::get()' – occurs for a lot of people, it seems. There are many suggested workarounds and hacks, but none of my attempts to find one that works have been successful. Apparently this error relates to an attempt to link against the static libraries of Boost, which is actually what I want.

I tried the -v option for CMake, to see what the linker command is:

$ cmake --build . -v
...
[ 50%] Linking CXX executable log_demo
/usr/bin/cmake -E cmake_link_script CMakeFiles/log_demo.dir/link.txt --verbose=1
/usr/bin/c++ -m64 -g -m64 CMakeFiles/log_demo.dir/log_demo.cpp.o -o log_demo 
...

I see no mention of any Boost libraries on that c++ command line – that seems wrong to me. Why isn’t there a -lboost_log and -lboost_log_setup present?

This must be the fourth time in ten years I’ve tried to set up Boost.Log, each time it’s different (due to Conan changes, or CMake changes), so I’m hoping I’m missing something really obvious here…