Re: AC_CHECK_HEADER question

[Zack Weinberg]

On Sun, Mar 17, 2013 at 5:35 PM, Jan van Dijk <address@hidden> wrote:
>
> That is a bit disappointing, though: it generates a lot of extra work for the
> configure.ac author, only to find out what autoconf already knows: where it
> could find a particular header file. It will also make the scripts less
> robust.

Thing is, Autoconf *doesn't* know where the header is.  When you do

AC_CHECK_HEADER([superlu/slu_util.h])

that gets translated to something along the lines of

printf '#include <%s>\n' 'superlu/slu_util.h' > conftest.c
if $CC $CFLAGS $CPPFLAGS -c -o conftest.o conftest.c >>config.log 2>&1
then
  action-if-found
else
  action-if-not-found
fi

So it's the *C compiler* that searches for the header file, and it
doesn't tell the configure script where it found it.

You could do something like this instead:

superlu_found=no
for sludir in '' 'superlu/' #...
do
  AC_CHECK_HEADER([${sludir}slu_util.h],
    [AC_DEFINE_UNQUOTED([SLU_SLU_UTIL_H], ["\"${sludir}slu_util.h\""],
      [Define to the proper way to include slu_util.h])
     AC_DEFINE_UNQUOTED([SLU_SLU_OTHER_H], ["\"${sludir}slu_other.h\""],
      [Define to the proper way to include slu_other.h])
     # ... all other slu headers that may be required ...
     superlu_found=yes
     break])
done
if test $superlu_found = no; then
  AC_MSG_FAILURE([unable to find superlu headers])
fi

You then write things like

#include SLU_SLU_UTIL_H

in your code.  Unfortunately, you need to define one of these macros
for _every_ SLU header you need.  You might think it was possible to
write a macro that would let you do

#include SLUHDR(slu_util.h)

but it isn't (because you cannot token-paste a letter with a /).


zw