I am using Dlib for face landmark detection for my academic project.
When I am running Dlib 19.2
Your project is not inheriting the include directorys. I think you set "D:\dlib-19.2\dlib-19.2" as the only include dir. Errors like "cannot open source file string" are not related to your code, they are related to your project settings.
Again, note that you should not add the dlib folder itself to your compiler's include path. Doing so will cause the build to fail because of name collisions (e.g. dlib/string.h with string.h from the standard library). Instead you should add the folder that contains the dlib folder to your include search path and then use include statements of the form #include . This will ensure that everything builds correctly.