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Why doesn't autoconf pass the AC_CHECK_HEADER test when the .h is file clearly available?

Asked 2011-05-25T18:21:05.327
11

I am having a bear of a time getting autoconf to check for the presence of a particular header file.

Let's call the header dependency "inky.h", and let's say that inky is a library that was installed (seperately) with the prefix set to "/usr/local". This put "inky.h" in /usr/local/inky/inky.h and libinky.so in /usr/local/lib.

Now, I'm trying to verify the presence of inky.h in my applications configure.ac as follows:

dnl # Setup temp LDFLAGS and look for inky library/header
LDFLAGS_SAVE=${LDFLAGS};
CPPFLAGS_SAVE=${CPPFLAGS};

dnl # Look for inky on the user specified inky install path
LDFLAGS ="-L${inky_library_path}";
CPPFLAGS="-I${inky_include_path}/inky";

AC_MSG_NOTICE([Looking for inky.h using: ${CPPFLAGS}]);

dnl # This check finds inky.h just fine.  This check was only used for debugging
AC_CHECK_FILE(
   [${inky_include_path}/inky/inky.h],
   [AC_MSG_NOTICE([Found inky.h])],
   [AC_MSG_NOTICE([Didn't find inky.h])]
   )

dnl # Look for the inky header file.  If it isn't found, terminate.
AC_CHECK_HEADER(inky.h,
    [],
    [AC_MSG_ERROR([Couldn't find or include inky.h])]
    )

This produces the following output from ./configure (after an autoreconf -vfi):

configure: Looking for inky.y in fetk include path: -I/usr/local/include/inky.y
checking for /usr/local/include/inky/inky.h... yes
configure: Found inky.h
checking inky.h usability... no
checking inky.h presence... yes
configure: WARNING: inky.h: present but cannot be compiled
configure: WARNING: inky.h:     check for missing prerequisite headers?
configure: WARNING: inky.h: see the Autoconf documentation
configure: WARNING: inky.h:     section "Present But Cannot Be Compiled"
configure: WARNING: inky.h: proceeding with the compiler's result
checking for inky.h... no
configure: error: Couldn't find or include inky.h

Now, this appears to be the case because inky.h includes 2 other headers, so I add them in on the fourth

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2 Answers

10

I found what the issue was. The library that I am working with is a C library, but the "inky" library that I am linking against is a C++ library. So, the language (AC_LANG) was set to C early in the configure.ac script. While performing checks for "inky", I needed to change the language to C++ so that Autoconf used the C++ compiler instead of the C compiler. This was done rather easily by using:

AC_LANG_PUSH([C++])
dnl # Do the checks for inky
AC_LANG_POP([C++])

This solved both the problem that I asked about in this thread, and on that I hand't posted yet wherein I couldn't get the AC_CHECK_LIB macro to work.

Thank you everyone for your input.

answered 2011-05-25T19:33:29.860
3

The details about why this test is failing are in config.log. My guess is though, that:

  • Since you're not adding the path found with AC_CHECK_FILE to CPPFLAGS or INCLUDES or whatever autoconf is using these days.
  • AC_CHECK_HEADER does not find the header using preprocessor compilation (for another reason than the header being missing in CPPFLAGS includes).
answered 2011-05-25T18:37:42.117

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