C include paths: Safe to use hyphen & underscore?

Question

I realise that this may be operating-system specific, but I am trying to write cross-platform GCC code. So would like to know if it really is best to avoid these, or if am forced to choose, which would be the safer bet.

Answer 1

The syntax of header names is (C11, 6.4.7 par. 1):

header-name:
       < h-char-sequence >
       " q-char-sequence "
h-char-sequence:
       h-char
       h-char-sequence h-char
h-char:
          any member of the source character set except
                       the new-line character and >
q-char-sequence:
       q-char
       q-char-sequence q-char
q-char:
          any member of the source character set except
                       the new-line character and "

Both - and _ are part of the basic source character set (5.2.1 par. 3). But the standard leaves much stuff related to #include implementation-defined.

In practice I don't see any problems in using them. I'm not aware of a file system that disallows or assigns a special meaning to them. This Wikipedia article doesn't list one either.