(posting to the boost-users list and to the boost.m4 maintainer) I'm using autotools with the newest boost.m4 from http://repo.or.cz/w/boost.m4.git and have the following problem: I have several boost installations, among others a 1.34.1 in /usr/include and several in my homedir in /home/staff/ps/include/boost-1_36/ /home/staff/ps/include/boost-1_37/ /home/staff/ps/include/boost-1_39/ Calling configure with --with-boost=/home/staff/ps/include/boost-1_37/ I get the following information: checking for Boost headers version >= 103300... /home/staff/ps/include/boost-1_37/include checking for Boost's header version... 1_34_1 The first check finds the correct headers, the second one uses the wrong ones. configure.log says: ==== configure:20676: checking for a sed that does not truncate output configure:20755: result: /usr/bin/sed configure:20787: checking for Boost headers version >= 103300 configure:20841: g++ -c -g -O2 -I/home/staff/ps/include/boost-1_37/include conftest.cpp >&5 configure:20847: $? = 0 configure:20876: result: /home/staff/ps/include/boost-1_37/include configure:20886: checking for Boost's header version configure:20907: result: 1_34_1 configure:20938: checking boost/scoped_ptr.hpp usability configure:20955: g++ -c -g -O2 -I/home/staff/ps/include/boost-1_37/include conftest.cpp >&5 configure:20961: $? = 0 configure:20975: result: yes configure:20979: checking boost/scoped_ptr.hpp presence configure:20994: g++ -E -I/home/staff/ps/include/boost-1_37/include conftest.cpp configure:21000: $? = 0 configure:21014: result: yes ==== So only the one check does not use the newly found CPPFLAGS. I also saw that the header check is done WITHOUT using _AC_DO_STDERR so the actual g++ call for the header check is not shown. Unfortunately I did not succeed in changing the check to use _AC_DO_STDERR so I'm writing this mail instead of sending a patch suggestion. Regards, Peter Schüller -- Peter Schüller Institute of Information Systems, Vienna University of Technology Favoritenstrasse 9-11/1843, A-1040 Vienna, Austria T: +43 (1) 58801-18470 E: ps AT kr DOT tuwien DOT ac DOT at Homepage: http://www.kr.tuwien.ac.at/staff/ps/ TU Wien DVR: 0005886