Cannot link boost libraries with CMake - c++

Question

I have a sample C++ code that uses boost (program options module) as shown below:
#include <iostream>
#include <boost/program_options/options_description.hpp>
#include <boost/program_options/parsers.hpp>
#include <boost/program_options/variables_map.hpp>
namespace po = boost::program_options;
int main(int argc, const char* argv[]){
po::options_description description("MyTool Usage");
description.add_options()
("help,h", "Display this help message")
("version,v", "Display the version number");
po::positional_options_description p;
po::variables_map vm;
po::store(po::command_line_parser(argc, argv).options(description).positional(p).run(), vm);
po::notify(vm);
if(vm.count("help")){
std::cout << description;
return 0;
}
if(vm.count("version")){
std::cout << "MyTool Version 1.0" << std::endl;
return 0;
}
return 0;
}
I tried to compile using cmake. The corresponding CMakeLists.txt file is shown below:
cmake_minimum_required(VERSION 2.6)
set(CMAKE_CXX_LINK_FLAGS "-std=c++11 -g -Wall -fsigned-char -lboost_program_options-mt")
set(BOOST_ROOT /opt/local/include/boost)
set(BOOST_LIBRARYDIR /opt/local/lib)
find_package(Boost COMPONENTS program_options system filesystem REQUIRED)
include_directories(${BOOST_INCLUDE_DIR})
link_libraries(${BOOST_LIBRARIES})
add_executable(testboostpo testboostpo_simple.cpp)
target_link_libraries(testboostpo ${Boost_LIBRARIES})
Although cmake . seems to succeed and it also detects all the boost modules I typically use (program options, system, filesystem),
$ cmake .
-- The C compiler identification is GNU 5.5.0
-- The CXX compiler identification is GNU 5.5.0
-- Checking whether C compiler has -isysroot
-- Checking whether C compiler has -isysroot - yes
-- Checking whether C compiler supports OSX deployment target flag
-- Checking whether C compiler supports OSX deployment target flag - yes
-- Check for working C compiler: /opt/local/bin/gcc-mp-5
-- Check for working C compiler: /opt/local/bin/gcc-mp-5 -- works
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Detecting C compile features
-- Detecting C compile features - done
-- Checking whether CXX compiler has -isysroot
-- Checking whether CXX compiler has -isysroot - yes
-- Checking whether CXX compiler supports OSX deployment target flag
-- Checking whether CXX compiler supports OSX deployment target flag - yes
-- Check for working CXX compiler: /opt/local/bin/g++-mp-5
-- Check for working CXX compiler: /opt/local/bin/g++-mp-5 -- works
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Boost version: 1.66.0
-- Found the following Boost libraries:
-- program_options
-- system
-- filesystem
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/params/libraries/coding_interview/every_test/boost_test
the next step make fails with the following error:
$ make
Scanning dependencies of target testboostpo
[ 50%] Building CXX object CMakeFiles/testboostpo.dir/testboostpo_simple.cpp.o
[100%] Linking CXX executable testboostpo
ld: library not found for -lboost_program_options-mt
collect2: error: ld returned 1 exit status
make[2]: *** [testboostpo] Error 1
make[1]: *** [CMakeFiles/testboostpo.dir/all] Error 2
make: *** [all] Error 2
There seems to be a problem linking boost library for program options. However, I can see that the library is installed at /opt/local/lib/libboost_program_options-mt.dylib
Alternatively, I also tried isolating the compilation but it fails as well.
$ g++ -L/opt/local/lib testboostpo_simple.cpp -lboost_program_options-mt
Undefined symbols for architecture x86_64:
"boost::program_options::to_internal(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)", referenced from:
std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > boost::program_options::to_internal<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >(std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&) in ccg8tggM.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status
$ g++ -L/opt/local/lib testboostpo_simple.cpp /opt/local/lib/libboost_program_options-mt.dylib
Undefined symbols for architecture x86_64:
"boost::program_options::to_internal(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)", referenced from:
std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > boost::program_options::to_internal<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >(std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&) in ccg8tggM.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status
I am using gcc5, boost 1.66 and cmake 3.12 (all of them installed using macports).
boost header files are in location:
/opt/local/include/boost/
and the boost library files are in location:
/opt/local/lib
Does anybody here know what might be causing the boost linking to still fail despite providing the paths? Anything else missing here or incorrectly specified?
Thanks,

Answer 1

Because you have used the CMAKE_CXX_LINK_FLAGS, and cmake will check it first instead of using your target_link_libraries, if you want to do it by yourself, you need to add -L/opt/local/lib as well, the simpler way is let cmake do it for you. The following is my example:
cmake_minimum_required(VERSION 2.6)
project(server CXX)
set(CXX_FLAGS
-g
-Wall
)
# set(Boost_NO_SYSTEM_PATHS ON)
set(BOOST_ROOT /mnt/d/Code/boost)
set(BOOST_LIBRARYDIR /mnt/d/Code/boost/stage/lib)
find_package(Threads REQUIRED)
find_package(Boost 1.68.0 COMPONENTS program_options REQUIRED)
file(GLOB SRC
"*cpp*"
)
if(Boost_FOUND)
include_directories(${Boost_INCLUDE_DIRS})
message(${Boost_PROGRAM_OPTIONS_LIBRARIES})
add_executable(main ${SRC})
target_link_libraries(main Threads::Threads ${Boost_PROGRAM_OPTIONS_LIBRARIES})
endif()
Besides, if you build it separately, you should first compile the object then link, or it may turn into undefined reference. In your case, you should link at the last, the result will be different when you put the link in the front or the tail, I am sorry I don't why this happening.

Answer 2

It looks like you're trying to link a 32-bit library against a 64-bit build. The hint is ld: symbol(s) not found for architecture x86_64.
Linking libraries requires that you match the exact build type. Here's some more info about the linking process.
https://www.boost.org/doc/libs/1_63_0/more/getting_started/windows.html