You didn't write anything about your platform, but a wild guess: bitness-mismatch; e.g., trying to link a 32-bit object file with a 64-bit library.

Also, you're running nm on the wrong files to check for symbols. If you're linking statically, you should run nm on the .a files, not on the .so files.

From: Boost-users <boost-users-bounces@lists.boost.org> on behalf of Jyoti Sharma via Boost-users <boost-users@lists.boost.org>
Sent: Friday, September 15, 2017 12:10:25 PM
To: boost-users@lists.boost.org
Cc: Jyoti Sharma
Subject: [Boost-users] Linker error when using Boot regex on AIX

I am using boost_1_61_0. In my code I have:

#include <boost/regex.hpp>
static boost::regex testxp("[");

I have these libraries:
   libboost_regex.a libboost_regex.so

I can see these libraries have symbols:
   LIBRARY: Shared object libboost_regex.so: 136 symbols imported.
   LIBRARY: Shared object libboost_system.so: 7 symbols imported.

To build my program I have added these linking options:
   -Wl,-bnoquiet -Wl,-Bstatic -lboost_regex -lboost_system -Wl,-Bdynamic

But I get this error during linking:
   ld: 0711-317 ERROR: Undefined symbol: .boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::do_assign(char const*, char const*, unsigned int)

But that symbol is there:
machine:/home> nm libboost_regex.so nm libboost_regex.so |grep do_assign
._ZN5boost11basic_regexIcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEE9do_assignEPKcS7_j T   268508592
machine:/home> c++filt ._ZN5boost11basic_regexIcNS_12regex_traitsIcNS_16cpp_regex_traitsIcEEEEE9do_assignEPKcS7_j
.boost::basic_regex<char, boost::regex_traits<char, boost::cpp_regex_traits<char> > >::do_assign(char const*, char const*, unsigned int)