Referencing external files in Eclipse: virtually linked files vs build settings in Project Properties?

Question

There is information on the web as well as here on the topic related to the using external file resources in CDT Eclipse: C/C++ and H files located somewhere else in the files system. All the described methods run along two methods:

1. creation within the project space the virtual linked files which point to the locations of the actual files without copying them
2. adding the location of the external referenced resource in the Project->Properties->C/C++ general->Paths and Symbols and related Project->Properties-> C/C++ Build (link folders and includes)

I am not sure if the 1st method is always enough without adding the 2nd, but seems the 2nd builds well without the 1st.

My question is about a comparison of the two. Are those methods intended to be used similarly or each one is preferred in some cases?

Is each method self sufficient without applying the other?

This forum thread https://www.eclipse.org/forums/index.php/t/1087314/ suggests that for the include files the 1st method might not even be sufficient as the Build Settings should still be updated (2nd method) to include the linked H files...then may be the 1st method is irrelevant?

Answer 1

You would typically use the first method if you want to edit the externally-located files as part of your work on the project, and the second method if they're just dependencies that you use without modifying.

On a technical level, the difference is that with the first method the files will be part of the project model, and so will e.g. show up as candidates in Open Resource, while with the second method they wouldn't. Another difference is that with the first method, the files are indexed independently, while with the second method the files are only indexed by virtue of being included by files in your project (so e.g. .cpp files in those directories typically wouldn't be indexed with the second method at all).

Update: answers to questions from the comment

Is the 1st method sufficient enough in all cases without updating Paths and Symbols Property ?

No, if there are header files located in the linked directory that are included by files in your project using include paths that are not relative to the current directory (so not just #include "foo.h" in the same directory, #include "../foo.h" in a child directory, etc., but #include <bar/foo.h> in some other directory), you still want to specify those include paths in Paths and Symbols.

CDT's indexer does have an "Allow heuristic resolution of includes" option (specified in Preferences -> C/C++ -> Indexer) that may allow you to avoid adding the paths to Paths and Symbols, but note that (1) this affects the indexer only, not the build (which may be fine if you're using your own makefiles for the build), and (2) as it's heuristic, it's not perfect, e.g. if you have headers with the same name in different directories it can get confused. For best accurracy, I recommend unchecking "Allow heuristic resolution of includes", and always specifying include paths explicitly.

Also can the 2nd method be sufficient in itself if referenced files to be used AS IS without modification?

I don't see why not.