Re: bug while compiling kvirc CVS - told me to report it to you. :)

[Akim Demaille]

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 address@hidden ##
     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 received the below error:
################################################################################
### Initializing libtool
################################################################################
checking for ld used by GCC... /usr/i386-slackware-linux/bin/ld
checking if the linker (/usr/i386-slackware-linux/bin/ld) is GNU ld... yes
checking for /usr/i386-slackware-linux/bin/ld option to reload object files... 
-r
checking for BSD-compatible nm... /usr/bin/nm -B
checking for a sed that does not truncate output...
checking whether ln -s works... yes
checking how to recognise dependant libraries... pass_all
checking dlfcn.h usability... yes
checking dlfcn.h presence... no
configure: WARNING: dlfcn.h: accepted by the compiler, rejected by the 
preprocessor!
configure: WARNING: dlfcn.h: proceeding with the preprocessor's result
configure: WARNING:     ## ------------------------------------ ##
configure: WARNING:     ## Report this to address@hidden ##
configure: WARNING:     ## ------------------------------------ ##
checking for dlfcn.h... no
checking how to run the C++ preprocessor... g++ -E



System: Slackware 9.0.0
gcc 3.2.2
autoconf (GNU Autoconf) 2.57
automake (GNU automake) 1.7.3

Hope this helps!

Kevin