header guards from different files might be the same?

[dirk-thomas]

cpplint uses a specific pattern for the header guards of a file. It looks to me that this pattern can lead to the same PP variable for different headers (with different names and paths).

Let me describe a simple scenario with two files:

• include/foo_bar/baz.h
• include/foo/bar_baz.h

Following cpplint rules both of them would end up using the header guard variable FOO_BAR_BAZ_H_.

Am I missing something or is this really the case? If it is, wouldn't it be better to change the rule to make these two result in different variables? E.g. a path separator could be transformed into a double underscore which would result in two different variables:

• FOO_BAR__BAZ_H_
• FOO__BAR_BAZ_H_

[chen3feng]

Then, how about:
foo__bar.h
foo/bar.h

[dirk-thomas]

There are only two options:

• either choose a separator which can not occur in a file name or
• choose a sequence (like double underscore) which is a) uncommon in file names and b) should be discourage to use in http://google.github.io/styleguide/cppguide.html#File_Names

Since I don't see which character would be allowed in a preprocessor name which isn't in a filename I suggested a double underscore. But any sequence would be subject to a potential collision if it is allowed in a filename.