error when including header-only library to my project using cmake - c++

Question

I am trying to add this header-only library to my project : https://github.com/CPPAlliance/url
My project structure :
├── build
│   ├── build.ninja
│   ├── CMakeCache.txt
│   ├── CMakeFiles
│   │   ├── 3.18.0-rc1
│   │   │   ├── CMakeCCompiler.cmake
│   │   │   ├── CMakeCXXCompiler.cmake
│   │   │   ├── CMakeDetermineCompilerABI_C.bin
│   │   │   ├── CMakeDetermineCompilerABI_CXX.bin
│   │   │   ├── CMakeSystem.cmake
│   │   │   ├── CompilerIdC
│   │   │   └── CompilerIdCXX
│   │   ├── cmake.check_cache
│   │   ├── CMakeError.log
│   │   ├── CMakeOutput.log
│   │   ├── CMakeTmp
│   │   ├── cmake.verify_globs
│   │   ├── hftbot.dir
│   │   │   ├── build.make
│   │   │   ├── cmake_clean.cmake
│   │   │   ├── CXX.includecache
│   │   │   ├── DependInfo.cmake
│   │   │   ├── depend.internal
│   │   │   ├── depend.make
│   │   │   ├── flags.make
│   │   │   ├── link.txt
│   │   │   ├── progress.make
│   │   │   └── src
│   │   ├── Makefile2
│   │   ├── Progress
│   │   │   ├── 1
│   │   │   └── count.txt
│   │   ├── progress.marks
│   │   ├── rules.ninja
│   │   ├── TargetDirectories.txt
│   │   └── VerifyGlobs.cmake
│   ├── cmake_install.cmake
│   ├── compile_commands.json
│   ├── details.json
│   ├── external
│   │   ├── json
│   │   │   ├── CMakeFiles
│   │   │   └── cmake_install.cmake
│   │   └── url
│   │   ├── CMakeFiles
│   │   └── cmake_install.cmake
│   ├── hftbot
│   ├── Makefile
│   └── src
│   ├── CMakeFiles
│   │   ├── CMakeDirectoryInformation.cmake
│   │   └── progress.marks
│   ├── cmake_install.cmake
│   └── Makefile
├── build.sh
├── CMakeLists.txt
├── configure.sh
├── details.json
├── external
│   └── urlib
│   ├── build
│   │   └── Jamfile
│   ├── cmake
│   │   ├── config.cmake.in
│   │   └── toolchains
│   ├── CMakeLists.txt
│   ├── doc
│   │   ├── images
│   │   ├── Jamfile
│   │   ├── javadoc.hpp
│   │   ├── qbk
│   │   ├── README.md
│   │   ├── tools
│   │   └── xsl
│   ├── extra
│   │   ├── include
│   │   └── test_main.cpp
│   ├── include
│   │   └── boost
│   ├── Jamfile
│   ├── LICENSE_1_0.txt
│   ├── meta
│   │   ├── explicit-failures-markup.xml
│   │   └── libraries.json
│   ├── README.md
│   ├── src
│   │   └── src.cpp
│   └── test
│   ├── CMakeLists.txt
│   ├── Jamfile
│   ├── limits
│   ├── unit
│   └── wpt
├── run.sh
└── src
├── CMakeLists.txt
├── httpClient.cpp
└── WebsocketClient.cpp
CMakeLists.txt in the root folder :
cmake_minimum_required(VERSION 3.18.0)
project(hftbot)
find_package(Boost 1.79.0 REQUIRED COMPONENTS system thread filesystem container)
find_package(Threads REQUIRED)
add_subdirectory(src)
include_directories(SYSTEM external/urlib/include)
set(URLIB_DIRECTORY "external/urlib/include")
set(URLIB_HEADERS ${URLIB_DIRECTORY}/boost/url.hpp ${URLIB_DIRECTORY}/boost/url/src.hpp)
set(SOURCES src/httpClient.cpp)
add_executable(${PROJECT_NAME} ${SOURCES} ${URLIB_HEADERS})
target_include_directories(${PROJECT_NAME} PRIVATE ${URLIB_DIRECTORY})
As you can see i used target_include_directories() to include header files into my project.
but it seems that something is wrong here.
#include <boost/url.hpp>
#include <boost/url/src.hpp>
When i try to include this one, it is showing me build error :
/usr/local/bin/cmake -S/home/user/Desktop/HFTBOT -B/home/user/Desktop/HFTBOT/build --check-build-system CMakeFiles/Makefile.cmake 0
-- Configuring done
-- Generating done
-- Build files have been written to: /home/user/Desktop/HFTBOT/build
/usr/local/bin/cmake -E cmake_progress_start /home/user/Desktop/HFTBOT/build/CMakeFiles /home/user/Desktop/HFTBOT/build//CMakeFiles/progress.marks
make -s -f CMakeFiles/Makefile2 all
Scanning dependencies of target hftbot
CMake Error: Directory Information file not found
[ 50%] Building CXX object CMakeFiles/hftbot.dir/src/httpClient.cpp.o
/home/user/Desktop/HFTBOT/src/httpClient.cpp:11:10: fatal error: boost/url/src.hpp: No such file or directory
11 | #include "boost/url/src.hpp"
| ^~~~~~~~~~~~~~~~~~~
compilation terminated.
make[2]: *** [CMakeFiles/hftbot.dir/build.make:83: CMakeFiles/hftbot.dir/src/httpClient.cpp.o] Error 1
make[1]: *** [CMakeFiles/Makefile2:116: CMakeFiles/hftbot.dir/all] Error 2
make: *** [Makefile:104: all] Error 2
I got a feeling that is it because of the location of executable that produce this error ?

Answer 1

Since your source is not in the project root but in src/ you might have to specify the relative path using ../external/url/include. A more typical approach in CMake is to use absolute paths:
set(URLIB_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/external/urlib/include")
I created a self-contained example with instructions to build here: https://github.com/sehe/BoostURLAsSubmodule/tree/main
BoostURLAsSubmodule
Steps to build:
git clone --recurse-submodules https://github.com/sehe/BoostURLAsSubmodule
cd BoostURLAsSubmodule/
cmake -B build .
make -C build/
If you need, override BOOST_ROOT:
BOOST_ROOT=~/custom/boost_1_79_0/ cmake -B build .