AC_CHECK_FILES on /dev/stdin

[David Fang]

Hi,
        I naively tried to use AC_CHECK_FILE(S) on /dev/stdin /dev/stdout
and /dev/stderr to detect their presence, but the test result is 'no' for
these 'files'.  The result is 'yes', however, for /dev/null.
        Is there a more appropriate test for the presence of these special
files?  or do I need to roll my own macro-test using something like
"test -f"?  (Or am I checking for something that should/need
not be checked?)  Suggestions?
        Thanks!

David