Problem linking print_helper_t<nullptr_t> under Clang

[Tony Lewis <TonyELewis@…>]

I'm trying out 1.64.0 b2...

I can get the following code to compile, link and run under GCC :

#define BOOST_TEST_DYN_LINK

#include <boost/test/unit_test.hpp>

BOOST_AUTO_TEST_CASE( plv_tc ) {
        BOOST_TEST( nullptr == nullptr );
}

bool init_function() { return true; }
int main( int argc, char* argv[] ) {
        return ::boost::unit_test::unit_test_main( &init_function, argc, argv );
}

...with commands:

setenv BOOST_ROOT /opt/boost_1_64_0_b2_gcc_build
setenv LD_LIBRARY_PATH $BOOST_ROOT/lib
g++ -std=c++11 -isystem $BOOST_ROOT/include boost-test.nullptr-problem.cpp -L$BOOST_ROOT/lib -lboost_unit_test_framework-mt
./a.out

...but if I try with Clang:

setenv BOOST_ROOT /opt/boost_1_64_0_b2_clang_build
setenv LD_LIBRARY_PATH $BOOST_ROOT/lib
clang++ -std=c++11 -stdlib=libc++ -isystem $BOOST_ROOT/include boost-test.nullptr-problem.cpp -L$BOOST_ROOT/lib -lboost_unit_test_framework-mt

...I get:

/tmp/boost-test-fe7931.o: In function `std::__1::basic_ostream<char, std::__1::char_traits<char> >& boost::test_tools::tt_detail::operator<< <decltype(nullptr)>(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, boost::test_tools::tt_detail::print_helper_t<decltype(nullptr)> const&)':
boost-test.nullptr-problem.cpp:(.text._ZN5boost10test_tools9tt_detaillsIDnEERNSt3__113basic_ostreamIcNS3_11char_traitsIcEEEES8_RKNS1_14print_helper_tIT_EE[_ZN5boost10test_tools9tt_detaillsIDnEERNSt3__113basic_ostreamIcNS3_11char_traitsIcEEEES8_RKNS1_14print_helper_tIT_EE]+0x26): undefined reference to `boost::test_tools::tt_detail::print_log_value<decltype(nullptr)>::operator()(std::__1::basic_ostream<char, std::__1::char_traits<char> >&, decltype(nullptr))'
clang: error: linker command failed with exit code 1 (use -v to see invocation)

I may well just be doing something stupid - apologies if so.

I'm using Clang++ 3.8.1 and GCC 6.2.0 on Ubuntu 16.10 (Linux 4.8.0-46-generic; x86_64).

[Tony E Lewis <TonyELewis@…>]

AFAUI, what's going on is:

• I'm building my code in C++14 mode, which causes the Boost Test code to provide a specialisation of print_log_value<> for nullptr_t with a declaration (but not definition) of its operator().
• I'm linking against Boost libraries that were built without any standard specified. In GCC 7.2.0 means ~C++14 but in Clang 4.0.1 means ~C++03. So the Clang-built library I'm linking against doesn't provide any definition of print_log_value<std::nullptr_t>::operator().

I can work around this. However it may make things a bit simpler to either:

• provide an inline definition of print_log_value<std::nullptr_t>::operator() in the .hpp rather than in a separate .ipp, or failing that
• not specialise print_log_value<> for nullptr_t at all and leave it for users to do themselves if they wish.

[Raffi Enficiaud]

Thanks, I was not able to reproduce initially the issue, but with the last information I understand better what the issue is.

[Raffi Enficiaud]

In branch topic/12969-problems-nullptr. It would be good if you tell me if this fixes your issue, as it is not possible to have a unit test covering this.

[Raffi Enficiaud]

On develop

[Raffi Enficiaud]

On master

[Tony E Lewis <tonyelewis@…>]

Thanks very much for this fix.

Apologies - I didn't see the message asking for a check. Yes - that works for me.