I would like to compile & link the following demo application using boost::logger
but I get the following output:
d$ rm -rf *; cmake ..;make
-- The C compiler identification is GNU 5.4.0
-- The CXX compiler identification is GNU 5.4.0
-- Check for working C compiler: /usr/bin/cc
-- Check for working C compiler: /usr/bin/cc -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Check for working CXX compiler: /usr/bin/c++
-- Check for working CXX compiler: /usr/bin/c++ -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Boost version: 1.67.0
-- Boost_LIBRARIES:
--
-- BOOST_INCLUDEDIR:
-- /path/to/env/include
-- Configuring done
-- Generating done
-- Build files have been written to: /path/to/src/tmp/logger/build
Scanning dependencies of target logger
[ 50%] Building CXX object CMakeFiles/logger.dir/logger.cpp.o
[100%] Linking CXX executable logger
CMakeFiles/logger.dir/logger.cpp.o: In function `init()':
/path/to/src/tmp/logger/logger.cpp:21: undefined reference to `boost::log::v2_mt_posix::core::get()'
/path/to/src/tmp/logger/logger.cpp:24: undefined reference to `boost::log::v2_mt_posix::core::set_filter(boost::log::v2_mt_posix::filter const&)'
CMakeFiles/logger.dir/logger.cpp.o: In function `boost::log::v2_mt_posix::attribute_name::attribute_name(char const*)':
/path/to/env/include/boost/log/attributes/attribute_name.hpp:80: undefined reference to `boost::log::v2_mt_posix::attribute_name::get_id_from_string(char const*)'
CMakeFiles/logger.dir/logger.cpp.o: In function `boost::log::v2_mt_posix::aux::light_rw_mutex::light_rw_mutex()':
/path/to/env/include/boost/log/detail/light_rw_mutex.hpp:103: undefined reference to `pthread_rwlock_init'
CMakeFiles/logger.dir/logger.cpp.o: In function `boost::log::v2_mt_posix::aux::light_rw_mutex::~light_rw_mutex()':
/path/to/env/include/boost/log/detail/light_rw_mutex.hpp:107: undefined reference to `pthread_rwlock_destroy'
CMakeFiles/logger.dir/logger.cpp.o: In function `boost::log::v2_mt_posix::aux::light_rw_mutex::lock_shared()':
/path/to/env/include/boost/log/detail/light_rw_mutex.hpp:111: undefined reference to `pthread_rwlock_rdlock'
CMakeFiles/logger.dir/logger.cpp.o: In function `boost::log::v2_mt_posix::aux::light_rw_mutex::unlock_shared()':
/path/to/env/include/boost/log/detail/light_rw_mutex.hpp:115: undefined reference to `pthread_rwlock_unlock'
CMakeFiles/logger.dir/logger.cpp.o: In function `boost::log::v2_mt_posix::aux::once_block_sentry::~once_block_sentry()':
...
...
now my CMakeLists.txt
looks like:
cmake_minimum_required(VERSION 2.6)
project(LOGGER)
set(BOOST_INCLUDEDIR "/path/to/env/include")
set(BOOST_ROOT "/path/to/env/include")
set(Boost_NO_SYSTEM_PATHS on CACHE BOOL "Do not search system for Boost")
find_package(Boost REQUIRED)
message(STATUS Boost_LIBRARIES:)
message (STATUS ${Boost_LIBRARIES})
message(STATUS BOOST_INCLUDEDIR:)
message(STATUS ${BOOST_INCLUDEDIR})
ADD_EXECUTABLE(logger logger.cpp)
target_include_directories(logger PUBLIC ${BOOST_INCLUDEDIR})
set (CMAKE_CXX_FLAGS "-g -Wall -DBOOST_LOG_DYN_LINK")
and logger.cpp
:
#include <iostream>
#include <boost/fusion/iterator/equal_to.hpp>
#include <boost/log/core.hpp>
#include <boost/log/trivial.hpp>
#include <boost/log/expressions.hpp>
#include <boost/log/utility/setup/file.hpp>
namespace logging = boost::log;
namespace src = boost::log::sources;
namespace sinks = boost::log::sinks;
namespace keywords = boost::log::keywords;
namespace expr = boost::log::expressions;
void init()
{
logging::add_file_log("sample.log");
logging::core::get()->set_filter
(
logging::trivial::severity >= logging::trivial::info
);
}
int main(void) {
init();
std::cout <<"Hello World!";
As you can see in the cmake output, ${Boost_LIBRARIES}
did not return anything, I suspect this to be the culprit even though, the compiler found the boost includes at the non-standard path.
There are a number of issues with your CMakeLists.
You haven't linked your executable against Boost, so although you will have access to the declarations of Boost functions from the headers found at ${Boost_INCLUDEDIR}
, you'll see undefined references to their definitions. Hence, you need to:
target_link_libraries(logger PRIVATE ${Boost_LIBRARIES})
This will resolve the linking issue.
Less problematically, your usage of CMAKE_CXX_FLAGS
has some issues. Using set()
for CMAKE_CXX_FLAGS
is deprecated, but the correct usage is:
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} <value>")
Because set() overwrites. However, the more modern way to do this would be:
target_compile_options(logger PRIVATE -g -Wall)
target_compile_definitions(logger PRIVATE BOOST_LOG_DYN_LINK=true)
This will ensure that these definitions are used only for this exectuable. Note that this step will require a relatively recent version of CMake.
The findBoost module exports a number of variables, one of which is ${Boost_INCLUDE_DIRS}
. This variable represents the directories in which boost files are stored. Boost also looks for a variable, ${BOOST_INCLUDEDIR}
, which is the path to the top-level directory of the boost headers. Currently, you're using the latter to represent the former, which should be corrected.
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