Facing problems in my first time handling CMake, Third party(header only) libraries

Question

I want to use the following library https://github.com/gmeuli/caterpillar

It's documentation says that it's a header-only library, and that I should "directly integrate it into my source files with #include <caterpillar/caterpillar.h>." It also depends on a few other libraries, one of which I need to use directly as well.

So far I have done the following:

1. create cmake project to make an 'executable' (with the vscode extension)
2. created a 'lib' folder, inside which I did

git clone https://github.com/gmeuli/caterpillar

3. Then, I did include_directories(lib) in my cmake file.
4. But #include <caterpillar/caterpillar.h> doesn't quite work in my singular main.cpp file.

I played around with various CMake functions, and it either gave the error "No such file or directory" regarding caterpillar/caterpillar.h itself, or it gave "cannot open source file... dependent of caterpillar/caterpillar.h" depending on how I messed with the cmake file.

For reference:

cat ~/project/main.cpp

#include <caterpillar/caterpillar.hpp>
#include <lorina/lorina.hpp> //how do I include this ? it's in the lib folder of caterpillar itself, or do I need to have a copy of it in my lib folder too

int main()
{
    // stuff in lorina:: namespace
    // stuff in caterpillar:: namespace
    return 0;
}

cat ~/project/CMakeLists.txt

include_directories(lib)
//... rest is stuff like CXX standard, etc etc

tree ~/project

main.cpp
lib/
    caterpillar/
build/
    cmake generated stuff
CMakeLists.txt

Answer 1

Firstly, modern cmake recommends target_include_directories() instead of old include_directories() for better scope management.

Actually <caterpillar/caterpillar.hpp> is not in $PROJECT_SOURCE_DIR/lib directory. That's why your code not works.

CMakeLists example:

cmake_minimum_required(VERSION 3.22)
project(myproject)

set(CMAKE_CXX_STANDARD 17)

add_executable(my_project main.cpp)

target_include_directories(my_project PRIVATE ${PROJECT_SOURCE_DIR}/lib/caterpillar/include)

# project_src_dir/lib/catepillar/include/ is the directory where you find the headers like <catepillar/catepillar.hpp>

target_include_directories(my_project PRIVATE ${PROJECT_SOURCE_DIR}/lib/caterpillar/lib/lorina)

caterpillar's document describes how to include their headers in a traditional style, assuming the readers could understand this and decide where to put the headers themselves. (which means you don't need the whole git repo but only the "include" dir.)

---

For this specific problem, the library has provided a detailed CMakeLists.txt for users to include:

cmake_minimum_required(VERSION 3.22)
project(my_project)

set(CMAKE_CXX_STANDARD 17)

add_subdirectory(lib/caterpillar)
# this works because "project_src_dir/lib/catepillar/CMakeLists.txt" exists.

add_executable(my_project main.cpp)
target_link_libraries(my_project PRIVATE caterpillar)
# you need to tell cmake to add all catepillar settings into your project