How to include external library in your lib? - c++

Question

I am writing a library which itself uses a header-only 3rd-party library.
Currently, even if I build it as a static library, the client code still needs to add that 3rd-party library as well, as it is declared in my library's header file.
What can I do so that everything that's used by my code, ends up in the static library and the client code doesn't have to include what I have included in the header file?
There was a similar question, but the answer doesn't seem to work for me as I am building the static library with all of its dependencies (i.e. the include paths are configured and builds are successful).
To give you a better view, this is how my Core.h looks like:
#ifndef CORE_H
#define CORE_H
#include <iostream>
#include <string>
#include <vector>
#include <functional>
#include <pybind11/pybind11.h>
#include <pybind11/embed.h>
#include <pybind11/stl.h>
#include <pybind11/functional.h>
#include <pybind11/numpy.h>
namespace py = pybind11;
using namespace py::literals;
typedef void(*CallbackFn)(bool, std::string, py::array_t<uint8_t>&);
typedef std::function<void(std::string)> LogFunction;
class Core
{
private:
py::scoped_interpreter guard{};
py::object cls;
py::object obj;
py::object startFunc;
py::object stopFunc;
py::object setCpuAffinityFunc;
py::object addCallbackFunc;
py::object removeCallbackFunc;
py::object getCallbacksFunc;
py::dict kwargs;
py::list callbackList;
public:
Core();
Core(bool showFeed);
...
As you can see, the issue here is the Pybind11 header-only library which is used in my code. Unfortunately, since these #include statements are included in my header file, the client code also needs to add pybind11 to their project in order for their project to build.
Is there any other way, other than converting all the py::* to void* and then including the header files in the Core.cpp file?

Answer 1

I found a solution for you. Consider your case: Client uses a library which uses a third library.
This can be assimilated by the following solution:
Client : .exe project is the client who know only Core project
Core : .lib project uses ThirdParty (Header_lib project) and can be used by Client project
Header_lib project is the ThirdParty lib
Solution configuration:
- Client Project depend from Core project:
-Core project depend from Header_Lib project:
In code:
Client create an instance cc of CCore object.
cc call useCoreParty function.
useCoreParty function uses ThirdParty
When i export core.lib:
DUMPBIN /SYMBOLS "G:\Core.lib" | findstr "useThirdParty"
I get:
This means that thirdparty part is included in your core.lib. Therefore, the client does not need to include thirdpaty's libs

Answer 2

I ended up using forward declaration, but not for the Pybind11 classes.
This is what I ended up doing :
//header file
#ifndef CORE_H
#define CORE_H
#include <iostream>
#include <string>
#include <vector>
#include <functional>
struct Wapper;
class Core
{
private:
Wapper* cls;
Wapper* obj;
Wapper* startFunc;
Wapper* stopFunc;
...
public:
Core();
...
};
and in the implementation file :
#include <pybind11/pybind11.h>
...
namespace py = pybind11;
using namespace py::literals;
struct Wrapper
{
py::object obj;
};
py::scoped_interpreter guard{};
Core::Core()
{
this->cls = new PyWrapper();
this->obj = new PyWrapper();
...
auto serviceUtilsModule = py::module::import("Module");
this->cls->obj = serviceUtilsModule.attr("SomeClass");
...
this->obj->obj = this->cls->obj(**kwargs);
...
}
This hides the pybind11 dependency from the client code and achieves what I was after!
Basically I forward declared a new type, made a pointer out of it and defined it inside the core.cpp. and since I defined in core.cpp I have many choices one of which was to add a py::object inside it and use that instead.
Side note:
I noticed the client project had to include Python's include and library folders or otherwise, it will complain about not finding Pybind11! This is truly bizarre! but since the client code will be running in an environment that must have a python package installed, its not an issue!
However, I'd also like to know why this is happening !