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)> _______________________________________________ Autoconf mailing list Autoconf@xxxxxxx http://lists.gnu.org/mailman/listinfo/autoconf