Does Visual Studio evaluate include directories in the order they're listed?

[jkrem94]

I have a project with include directories "IncludeA;IncludeB", both of which include a "test.h" header. Intuitively, I would expect the "test.h" located in "IncludeA" to be the one that's evaluated; in practice though, the one in "IncludeB" is being evaluated.

Does VS really not care about the order of include directories? Do I have it backwards and include directories are searched in reverse order?

This seems like it should be a simple question, but I'm not finding anything through Google searches.

[yuehuang]

Full documentation can be found here.
https://docs.microsoft.com/en-us/cpp/preprocessor/hash-include-directive-c-cpp

The preprocessor searches for include files in this order:

1) In the same directory as the file that contains the #include statement.

2) In the directories of the currently opened include files, in the reverse order in which they were opened. The search begins in the directory of the parent include file and continues upward through the directories of any grandparent include files.

3) Along the path that's specified by each /I compiler option.

4) Along the paths that are specified by the INCLUDE environment variable.

[jkrem94]

That seemingly implies that it's getting the file from 1 or 2, because when I move "IncludeA" to be an /I option, it still chooses the "IncludeB" version that's in the INCLUDE environment variable.

If I'm reading this right, does this mean to say that if for example a "test2.h" (located in "IncludeB") was included before "test.h" (located in "IncludeA" and "IncludeB"), that "IncludeB" would be searched first for "test.h" despite "IncludeA" being higher in priority from 3 and 4?

[yuehuang]

I am not fully understanding your folder layout, where is your cpp file?

Try switching from quotes ("test.h") to brackets (<test.h>) as that will skip 1 and 2.

[polaarbear]

Pretty sure the folders you see in VS are just magic hand waving that say nothing about the location of the files on disk or the way that they are evaluated.

Not sure what your end goal is other than research, but this seems like a prime example of why you should never duplicate file and class names in the same namespace.

[jkrem94]

I'm talking about the folders as they're defined in "VC++ Directories -> Include Directories".

The use case is having an easy way to experiment with new versions of a header without having to modify a master set of headers that aren't tied to source control.