Re: present but cannot be compiled (Was: bug)

[Akim Demaille]

Thanks for the bug report!

Unfortunately, the problem comes from the package itself, not from
Autoconf.  The configure.ac script needs to be updated.  Please, send
all this message (which your output attached) to the bug list (or the
authors) of the package you were trying to configure.

Below two parts of the Autoconf documentation are included: 1. the
documentation of AC_CHECK_HEADER(S), and 2. what's to be done to
upgrade configure.ac.

If you have some knowledge in C compilation, then there is something
more you can do to help: find out what are the prerequisite headers on
your system.

For instance, if the error message is:

       sys/socket.h: present but cannot be compiled
       sys/socket.h: check for missing prerequisite headers?
       sys/socket.h: proceeding with the preprocessor's result

then try to compile the program sample.c:

       #include <sys/socket.h>

with `cc -c sample.c'.  It will fail.  Then try to understand what
other headers are needed.  For instance, on Darwin, one needs:

       #include <stdio.h>
       #include <stdlib.h>
       #include <sys/socket.h>
       #include <sys/socket.h>

to get a successful compilation.  Then, send this additional
information to the package maintainers, together with a description of
your machine.

Thanks!

----------------------------------------------------------------------

Generic Header Checks
---------------------

   These macros are used to find system header files not covered by the
"particular" test macros.  If you need to check the contents of a header
as well as find out whether it is present, you have to write your own
test for it (*note Writing Tests::).

 - Macro: AC_CHECK_HEADER (HEADER-FILE, [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
     If the system header file HEADER-FILE is compilable, execute shell
     commands ACTION-IF-FOUND, otherwise execute ACTION-IF-NOT-FOUND.
     If you just want to define a symbol if the header file is
     available, consider using `AC_CHECK_HEADERS' instead.

     For compatibility issues with older versions of Autoconf, please
     read below.

 - Macro: AC_CHECK_HEADERS (HEADER-FILE..., [ACTION-IF-FOUND],
          [ACTION-IF-NOT-FOUND], [INCLUDES = `default-includes'])
     For each given system header file HEADER-FILE in the
     whitespace-separated argument list that exists, define
     `HAVE_HEADER-FILE' (in all capitals).  If ACTION-IF-FOUND is
     given, it is additional shell code to execute when one of the
     header files is found.  You can give it a value of `break' to
     break out of the loop on the first match.  If ACTION-IF-NOT-FOUND
     is given, it is executed when one of the header files is not found.

     For compatibility issues with older versions of Autoconf, please
     read below.

   Previous versions of Autoconf merely checked whether the header was
accepted by the preprocessor.  This was changed because the old test was
inappropriate for typical uses.  Headers are typically used to compile,
not merely to preprocess, and the old behavior sometimes accepted
headers that clashed at compile-time.  If you need to check whether a
header is preprocessable, you can use `AC_PREPROC_IFELSE' (*note
Running the Preprocessor::).

   This scheme, which improves the robustness of the test, also requires
that you make sure that headers that must be included before the
HEADER-FILE be part of the INCLUDES, (*note Default Includes::).  If
looking for `bar.h', which requires that `foo.h' be included before if
it exists, we suggest the following scheme:


AC_CHECK_HEADERS([foo.h])
AC_CHECK_HEADERS([bar.h], [], [],
[#if HAVE_FOO_H
# include <foo.h>
# endif
])

----------------------------------------------------------------------

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

   See *Note Particular Headers::, for a list of headers with their
prerequisite.

----------------------------------------------------------------------

Portability of Headers
----------------------

   This section tries to collect knowledge about common headers, and the
problems they cause.  By definition, this list will always require
additions.  Please help us keeping it as complete as possible.

`inttypes.h' vs. `stdint.h'
     Paul Eggert notes that: ISO C 1999 says that `inttypes.h' includes
     `stdint.h', so there's no need to include `stdint.h' separately in
     a standard environment.  Many implementations have `inttypes.h'
     but not `stdint.h' (e.g., Solaris 7), but I don't know of any
     implementation that has `stdint.h' but not `inttypes.h'.  Nor do I
     know of any free software that includes `stdint.h'; `stdint.h'
     seems to be a creation of the committee.

`net/if.h'
     On Darwin, this file requires that `sys/socket.h' be included
     beforehand.  One should run:

          AC_CHECK_HEADERS([sys/socket.h])
          AC_CHECK_HEADERS([net/if.h], [], [],
          [#include <stdio.h>
          #if STDC_HEADERS
          # include <stdlib.h>
          # include <stddef.h>
          #else
          # if HAVE_STDLIB_H
          #  include <stdlib.h>
          # endif
          #endif
          #if HAVE_SYS_SOCKET_H
          # include <sys/socket.h>
          #endif
          ])

`stdlib.h'
     On many systems (e.g., Darwin), `stdio.h' is a prerequisite.

`sys/socket.h'
     On Darwin, `stdlib.h' is a prerequisite.
Hi!
While running ./configure of libtool-1.5 on Darwin 6.5 I got

<snip>
configure: WARNING: mach-o/dyld.h: present but cannot be compiled
configure: WARNING: mach-o/dyld.h: check for missing prerequisite headers?
configure: WARNING: mach-o/dyld.h: proceeding with the preprocessor's result
configure: WARNING:     ## ------------------------------------ ##
configure: WARNING:     ## Report this to address@hidden ##
configure: WARNING:     ## ------------------------------------ ##
</snip>.

Still make worked fine.

Thanks for your work btw.

Bye, Robert




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checking whether we are using the GNU C compiler... yes
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yes
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yes
checking how to hardcode library paths into programs... immediate
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directory
darwin6.5 dyld
checking for dlopen in -ldl... (cached) yes
checking whether a program can dlopen itself... (cached) yes
checking whether a statically linked program can dlopen itself... (cached)
yes
configure: creating ./config.status
config.status: creating Makefile
config.status: creating doc/Makefile
config.status: creating tests/Makefile
config.status: executing depfiles commands
configure: configuring in libltdl
configure: running /bin/sh './configure' --prefix=/usr/local
--enable-ltdl-install --cache-file=/dev/null --srcdir=.
checking for a BSD-compatible install... /usr/bin/install -c
checking whether build environment is sane... yes
checking for gawk... no
checking for mawk... no
checking for nawk... no
checking for awk... awk
checking whether make sets $(MAKE)... yes
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 style of include used by make... GNU
checking dependency style of gcc... none
checking for an ANSI C-conforming const... yes
checking for inline... inline
checking build system type... powerpc-apple-darwin6.5
checking host system type... powerpc-apple-darwin6.5
checking for a sed that does not truncate output... /usr/bin/sed
checking for egrep... grep -E
checking for ld used by gcc... /usr/bin/ld
checking if the linker (/usr/bin/ld) is GNU ld... no
checking for /usr/bin/ld option to reload object files... -r
checking for BSD-compatible nm... /usr/bin/nm -p
checking whether ln -s works... yes
checking how to recognise dependent libraries... pass_all
checking how to run the C preprocessor... gcc -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
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checking for stdint.h... yes
checking for unistd.h... yes
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checking for dlfcn.h... yes
checking for g++... g++
checking whether we are using the GNU C++ compiler... yes
checking whether g++ accepts -g... yes
checking dependency style of g++... none
checking how to run the C++ preprocessor... g++ -E
checking for g77... g77
checking whether we are using the GNU Fortran 77 compiler... yes
checking whether g77 accepts -g... yes
checking the maximum length of command line arguments... 16384
checking command to parse /usr/bin/nm -p output from gcc object... ok
checking for objdir... .libs
checking for ar... ar
checking for ranlib... ranlib
checking for strip... strip
checking if gcc static flag  works... yes
checking if gcc supports -fno-rtti -fno-exceptions... yes
checking for gcc option to produce PIC... -fno-common
checking if gcc PIC flag -fno-common works... yes
checking if gcc supports -c -o file.o... yes
checking whether the gcc linker (/usr/bin/ld) supports shared libraries...
yes
checking how to hardcode library paths into programs... immediate
checking whether stripping libraries is possible... yes
checking dynamic linker characteristics... darwin6.5 dyld
checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... yes
configure: creating libtool
appending configuration tag "CXX" to libtool
checking for ld used by g++... /usr/bin/ld
checking if the linker (/usr/bin/ld) is GNU ld... no
checking whether the g++ linker (/usr/bin/ld) supports shared libraries...
yes
checking for g++ option to produce PIC... -fno-common
checking if g++ PIC flag -fno-common works... yes
checking if g++ supports -c -o file.o... yes
checking whether the g++ linker (/usr/bin/ld) supports shared libraries...
yes
checking how to hardcode library paths into programs... immediate
checking whether stripping libraries is possible... yes
checking dynamic linker characteristics... darwin6.5 dyld
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checking if libtool supports shared libraries... yes
checking whether to build shared libraries... yes
checking whether to build static libraries... yes
checking for g77 option to produce PIC... -fno-common
checking if g77 PIC flag -fno-common works... yes
checking if g77 supports -c -o file.o... yes
checking whether the g77 linker (/usr/bin/ld) supports shared libraries...
yes
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checking mach-o/dyld.h presence... yes
configure: WARNING: mach-o/dyld.h: present but cannot be compiled
configure: WARNING: mach-o/dyld.h: check for missing prerequisite headers?
configure: WARNING: mach-o/dyld.h: proceeding with the preprocessor's result
configure: WARNING:     ## ------------------------------------ ##
configure: WARNING:     ## Report this to address@hidden ##
configure: WARNING:     ## ------------------------------------ ##
checking for mach-o/dyld.h... yes
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configure: creating ./config.status
config.status: creating Makefile
config.status: creating config.h
config.status: executing depfiles commands