Unresolved external symbols with git submodules - c++

Question

I have a solution with 2 projects:
A static library (Almond)
A project that uses that static library (Sandbox)
I'm watching and following The Cherno's Game Engine Series except that I'm using C++20 modules. He added spdlog through git submodule add. I did the same thing. Then I added the $(SolutionDir)Almond\vendor\spdlog\include to Additional Include Directories in the Almond project.
The library builds fine (with a bunch of macro redefinition warnings from sal.h). When I try to build Sandbox I don't get any warnings just these errors:
Severity Code Description Project File Line Suppression State
Error LNK1120 4 unresolved externals Sandbox C:\source\Almond\bin\Debug-x64\Sandbox\Sandbox.exe 1
Error LNK2019 unresolved external symbol __imp_MapViewOfFileNuma2 referenced in function MapViewOfFile2 Sandbox C:\source\Almond\Sandbox\Almond.lib(stdout_color_sinks.h_D07BG2BYL2KQ67JA.obj) 1
Error LNK2001 unresolved external symbol __imp_MapViewOfFileNuma2 Sandbox C:\source\Almond\Sandbox\Almond.lib(spdlog.h_UEKL7NPFP4GR8605.obj) 1
Error LNK2001 unresolved external symbol "private: static class std::shared_ptr<class spdlog::logger> Almond::Log::s_CoreLogger" (?s_CoreLogger#Log#Almond##0V?$shared_ptr#Vlogger#spdlog###std##A::<!Log>) Sandbox C:\source\Almond\Sandbox\Almond.lib(Log.ixx.obj) 1
Error LNK2001 unresolved external symbol "private: static class std::shared_ptr<class spdlog::logger> Almond::Log::s_ClientLogger" (?s_ClientLogger#Log#Almond##0V?$shared_ptr#Vlogger#spdlog###std##A::<!Log>) Sandbox C:\source\Almond\Sandbox\Almond.lib(Log.ixx.obj) 1
Error LNK2001 unresolved external symbol "char const * const spdlog::details::os::default_eol" (?default_eol#os#details#spdlog##3QEBDEB) Sandbox C:\source\Almond\Sandbox\Almond.lib(Log.ixx.obj) 1
Relevant Code
Log.ixx (Almond):
export module Log;
import <memory>;
import <spdlog/spdlog.h>;
import <spdlog/sinks/stdout_color_sinks.h>;
export namespace Almond {
class Log {
private:
static std::shared_ptr<spdlog::logger> s_CoreLogger;
static std::shared_ptr<spdlog::logger> s_ClientLogger;
public:
static void Init() {
spdlog::set_pattern("%^[%T] %n: %v%$");
// Create multithreaded loggers
s_CoreLogger = spdlog::stdout_color_mt("ALMOND", spdlog::color_mode::always);
s_CoreLogger->set_level(spdlog::level::trace);
s_ClientLogger = spdlog::stdout_color_mt("APP", spdlog::color_mode::always);
s_ClientLogger->set_level(spdlog::level::trace);
}
inline static std::shared_ptr<spdlog::logger>& GetCoreLogger() { return s_CoreLogger; }
inline static std::shared_ptr<spdlog::logger>& GetClientLogger() { return s_ClientLogger; }
};
}
EntryPoint.ixx (Almond):
export module EntryPoint;
import Application;
import Log;
#ifdef ALMOND_PLATFORM_WINDOWS
export int main(int argc, char** argv) {
Almond::Log::Init();
auto app = Almond::CreateApplication();
app->Run();
delete app;
}
#endif
Main.cpp (Sandbox):
import Almond;
class Sandbox : public Almond::Application {
public:
Sandbox() {}
~Sandbox() {}
};
Almond::Application* Almond::CreateApplication() {
return new Sandbox();
}

Answer 1

A project that uses that static library
Is this project compiled as a shared (DLL) or static (.lib) library?
I assume you link your executable with the "A project that uses that static library". If so, you need to enable symbol visibility from that project.
I don't use VS, but CMake can handle that quite elegantly with GenerateExportHeader. You need to include __decl(dllexport) and __decl(dllimport) to your classes or make all symbol visibility public.
Windows makes all symbols private by default, while UNIX variants make them public by default.