I know this is a little old, but I don't know if the newer versions
of cURL have this fixed.

Ray

>To: Ray DeGennaro at Eaglerock IS <ray.degennaro_at_eriscorp.com>
>Cc: bug-autoconf_at_gnu.org
>Subject: Re: configure: WARNING: ## Report this to bug-autoconf_at_gnu.org.
> ##
>From: Akim Demaille <akim_at_epita.fr>
>Date: Fri, 28 Mar 2003 17:49:01 +0100
>User-Agent: Gnus/5.090016 (Oort Gnus v0.16) Emacs/21.2 (gnu/linux)
>Sender: Akim Demaille <akim_at_lrde.epita.fr>
>Status:
>
>
>Hi!
>
>Thanks for the report, unfortunately, it is about a problem in the
>package you were trying to configure, not from Autoconf itself.
>Please, forward this bug report to the authors of the package,
>together with the following piece of information. Thanks!
>
>Header Present But Cannot Be Compiled
>=====================================
>
> The most important guideline to bear in mind when checking for
>features is to mimic as much as possible the intended use.
>Unfortunately, old versions of `AC_CHECK_HEADER' and `AC_CHECK_HEADERS'
>failed to follow this idea, and called the preprocessor, instead of the
>compiler, to check for headers. As a result, incompatibilities between
>headers went unnoticed during configuration, and maintainers finally
>had to deal with this issue elsewhere.
>
> As of Autoconf 2.56 both checks are performed, and `configure'
>complains loudly if the compiler and the preprocessor do not agree.
>For the time being the result used is that of the preprocessor, to give
>maintainers time to adjust their `configure.ac', but in the near
>future, only the compiler will be considered.
>
> Consider the following example:
>
> $ cat number.h
> typedef int number;
> $ cat pi.h
> const number pi = 3;
> $ cat configure.ac
> AC_INIT
> AC_CHECK_HEADERS(pi.h)
> $ autoconf -Wall
> $ ./configure
> checking for gcc... gcc
> checking for C compiler default output... a.out
> checking whether the C compiler works... yes
> checking whether we are cross compiling... no
> checking for suffix of executables...
> checking for suffix of object files... o
> checking whether we are using the GNU C compiler... yes
> checking whether gcc accepts -g... yes
> checking for gcc option to accept ANSI C... none needed
> checking how to run the C preprocessor... gcc -E
> checking for egrep... grep -E
> checking for ANSI C header files... yes
> checking for sys/types.h... yes
> checking for sys/stat.h... yes
> checking for stdlib.h... yes
> checking for string.h... yes
> checking for memory.h... yes
> checking for strings.h... yes
> checking for inttypes.h... yes
> checking for stdint.h... yes
> checking for unistd.h... yes
> checking pi.h usability... no
> checking pi.h presence... yes
> configure: WARNING: pi.h: present but cannot be compiled
> configure: WARNING: pi.h: check for missing prerequisite headers?
> configure: WARNING: pi.h: proceeding with the preprocessor's result
> configure: WARNING: ## ------------------------------------ ##
> configure: WARNING: ## Report this to bug-autoconf_at_gnu.org. ##
> configure: WARNING: ## ------------------------------------ ##
> checking for pi.h... yes
>
>The proper way the handle this case is using the fourth argument (*note
>Generic Headers::):
>
> $ cat configure.ac
> AC_INIT
> AC_CHECK_HEADERS(number.h pi.h,,,
> [[#if HAVE_NUMBER_H
> # include <number.h>
> #endif
> ]])
> $ autoconf -Wall
> $ ./configure
> checking for gcc... gcc
> checking for C compiler default output... a.out
> checking whether the C compiler works... yes
> checking whether we are cross compiling... no
> checking for suffix of executables...
> checking for suffix of object files... o
> checking whether we are using the GNU C compiler... yes
> checking whether gcc accepts -g... yes
> checking for gcc option to accept ANSI C... none needed
> checking for number.h... yes
> checking for pi.h... yes
>
>
>----------------------------------------------------------------------
>
>I saw the following error message:
>checking net/if.h presence... yes
>configure: WARNING: net/if.h: present but cannot be compiled
>configure: WARNING: net/if.h: check for missing prerequisite headers?
>configure: WARNING: net/if.h: proceeding with the preprocessor's result
>configure: WARNING: ## ------------------------------------ ##
>configure: WARNING: ## Report this to bug-autoconf_at_gnu.org. ##
>configure: WARNING: ## ------------------------------------ ##
>checking for net/if.h... yes
>
>while running 'configure' for a library. Here's the results of 'uname -a':
>
>AIX imacs 1 4 0024DE2A4C00
>
>I don't know what other info you'd need.
>
>
>Ray

-- 
.=================================================================.
| =-=-=-=-=-=-= Eagle Rock Information Systems Corp =-=-=-=-=-=-= |
| -=-=-=-=-=-=- web and database business solutions -=-=-=-=-=-=- |
|   <http://www.eriscorp.com>        <mailto:info@eriscorp.com>   |
|Midwest Regional Office: 815-547-0662 (voice) 503-905-8153 (eFax)|
.=================================================================.
-------------------------------------------------------
Enterprise Linux Forum Conference & Expo, June 4-6, 2003, Santa Clara
The only event dedicated to issues related to Linux enterprise solutions
www.enterpriselinuxforum.com