How to use properly use cmake fetchcontent() to find or fetch boost

Question

What is the best way to add a dependency on Boost when using the CMake FetContent module.

In researching this issue I found this answer which seems to work fine for compiled boost libraries like thread or filesystem but does not work for header only libraries like asio.

For reference here is the CMakeLists.txt file that I've tested:

cmake_minimum_required(VERSION 3.24)
project(p)

set(BOOST_INCLUDE_LIBRARIES thread filesystem system)
set(BOOST_ENABLE_CMAKE ON)

include(FetchContent)
FetchContent_Declare(
  Boost
  GIT_REPOSITORY https://github.com/boostorg/boost.git
  GIT_TAG boost-1.74.0
)
FetchContent_MakeAvailable(Boost)

add_executable(boost_test boost_test.cpp)
target_link_libraries(boost_test PRIVATE Boost::boost Boost::filesystem)

And the corresponding boost_test.cpp file

#include <iostream>
#include <boost/asio.hpp>

int main(int argc, char * argv[])
{
    std::cout << "hello boost" << std::endl;
}

When I attempt to compile this project in Windows I get the following:

C:\builds\junk\boost_test\build>cmake --build .
MSBuild version 17.4.0+18d5aef85 for .NET Framework
  boost_atomic.vcxproj -> C:\builds\junk\boost_test\build\_deps\boost-build\libs\atomic\Debug\libboost_atomic-vc143-mt-
  gd-x64-1_80.lib
  boost_chrono.vcxproj -> C:\builds\junk\boost_test\build\_deps\boost-build\libs\chrono\Debug\libboost_chrono-vc143-mt-
  gd-x64-1_80.lib
  boost_container.vcxproj -> C:\builds\junk\boost_test\build\_deps\boost-build\libs\container\Debug\libboost_container-
  vc143-mt-gd-x64-1_80.lib
  boost_exception.vcxproj -> C:\builds\junk\boost_test\build\_deps\boost-build\libs\exception\Debug\libboost_exception-
  vc143-mt-gd-x64-1_80.lib
  boost_date_time.vcxproj -> C:\builds\junk\boost_test\build\_deps\boost-build\libs\date_time\Debug\libboost_date_time-
  vc143-mt-gd-x64-1_80.lib
  boost_filesystem.vcxproj -> C:\builds\junk\boost_test\build\_deps\boost-build\libs\filesystem\Debug\libboost_filesyst
  em-vc143-mt-gd-x64-1_80.lib
  boost_program_options.vcxproj -> C:\builds\junk\boost_test\build\_deps\boost-build\libs\program_options\Debug\libboos
  t_program_options-vc143-mt-gd-x64-1_80.lib
  boost_test.cpp
C:\builds\junk\boost_test\boost_test.cpp(2,10): fatal  error C1083: Cannot open include file: 'boost/asio.hpp': No such
 file or directory [C:\builds\junk\boost_test\build\boost_test.vcxproj]
  boost_thread.vcxproj -> C:\builds\junk\boost_test\build\_deps\boost-build\libs\thread\Debug\libboost_thread-vc143-mt-
  gd-x64-1_80.lib

Answer 1

You should also specify header-only libraries when using FetchContent with BOOST_INCLUDE_LIBRARIES

Like this

set(BOOST_INCLUDE_LIBRARIES thread filesystem system asio)

Also there is no target Boost::boost when using FetchContent so you should specify header-only libraries as non header-only here:

target_link_libraries(boost_test PRIVATE Boost::asio Boost::filesystem)