On Monday 18 Mar 2013 01:05:59 Zack Weinberg wrote: > On Sun, Mar 17, 2013 at 5:35 PM, Jan van Dijk <jan@xxxxxxxxxxxxxxxxxx> 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. Dear Zack, I guess my confusion stems from the fact that autoconf claims to check for presence and usability separately. Indeed, I just found out that 'presence' rather means that the file can be preprocessed. I did: AC_CHECK_HEADER([foo.h]) where foo.h contains: #error I do not exist To my surprise, configure tells me that foo.h does not exist, before pointing out that it is usable neither. Is that a documentation glitch? Would it be possible to provide a new macro AC_WHICH_HEADER, say, which informs it user what header has been/will be picked up by the preprocessor? Perhaps it could use the compiler's dependency tracking system, as in: echo "#include <math.h>" | gcc -E -M - | head -n1 | cut -f 3 -d ' ' I have no idea if this can be expressed in a sufficiently portable way that would allow its inclusion in autoconf. > You could do something like this instead: ... Thank you very much for that insightful suggestion. With kind regards, jan van Dijk. _______________________________________________ Autoconf mailing list Autoconf@xxxxxxx https://lists.gnu.org/mailman/listinfo/autoconf
