Ways to check for symbols

[Robert Lowe]

Hi!

After hunting for a bit, I came across several ways to check the
presence of a symbol in a header file.  I was interested in
INADDR_NONE, so I tried the following methods:

1) AC_CHECK_DECL: I had to experiment a bit with AC_CHECK_DECL --
   the vagueness in the existing documentation is outlined here:

http://lists.gnu.org/archive/html/bug-autoconf/2003-01/msg00006.html

  I landed on:

  AC_CHECK_DECL([INADDR_NONE], , , [#include <netinet/in.h>])


2) AC_CHECK_HEADER:

AC_CHECK_HEADER([netinet/in.h],
    AC_DEFINE(HAVE_NETINET_IN_H, 1,
              [Define to 1 if you have the <netinet/in.h> header file.])
    AC_MSG_CHECKING([for INADDR_NONE in netinet/in.h])
    AC_TRY_LINK([
                 #include <stdio.h>
                 #include <netinet/in.h>
                ], [ printf( "%xu", INADDR_NONE ); ],
                   [AC_MSG_RESULT(found) ],
                   [AC_MSG_RESULT(not found)
                    AC_DEFINE(NEED_INADDR_NONE, 1,
                     [Define to 1 if INADDR_NONE not present])])
    )

Then it occurred to me that I might be trying to pound in a thumb tack
with a sledgehammer, and that:

#ifndef INADDR_NONE
#define INADDR_NONE 0xffffffffU
#endif

...would do just fine.

So, just what are the merits, and possible pitfalls of any of these
approaches??

<Disclaimer>Still an autotools newbie!</Disclaimer>

--
Robert

A mind once stretched by a new idea never regains its original
dimension.  <Oliver Wendell Holmes Jr. (1841 - 1935)>