Include all source file for build - c++

Question

I have C++ project in my Visual Studio. Additionally I placed directory with source files in it in order to use them like library in my main project.
Everything works fine while code browsing. I can define includes of library headers and navigate to functions.
I got problem during project build. I got a lot of linking errors which tells that system can't link to functions from library.
Error LNK2019 unresolved external symbol lv_task_create referenced in function monitor_init testLVGL C:\cpp_test\testLVGL\monitor.obj 1
Error LNK2019 unresolved external symbol lv_tick_inc referenced in function "int __cdecl tick_thread(void *)" (?tick_thread##YAHPEAX#Z) testLVGL C:\cpp_test\testLVGL\testLVGL.obj 1
Error LNK2019 unresolved external symbol lv_task_handler referenced in function SDL_main testLVGL C:\cpp_test\testLVGL\testLVGL.obj 1
Looks like Visual C++ is even not trying to build library.
How to tell Visual C++ to include all library files located in subdirectory in order to build and link to project?

Answer 1

Visual Studio does not include all the files in a directory on its own. You need to explicitly include them (you dont have to do this if you add a file within the Solution Explorer or within Visual Studio). Else it wont be listed to the compiler.
To include them, go to the solution explorer and select "Show all files". This will show you all the files in the directory. Then you can see the unlisted files marked with a red icon. Right click it and hit "Include in project" and the red icon will disappear. After this, the file will be listed as one of the project's file.