Undefined refences when compiling example from the documentation

[ldpl]

I've build and installed version 7.9.0 and trying to compile "quick example" from https://pqxx.org/libpqxx/ with
g++ -lpq -lpqxx example.cpp gives a bunch of errors. Adding -std flags to the example or libpqxx compile doesn't help.

/usr/bin/ld: /tmp/ccW2W26H.o: in function `pqxx::internal::(anonymous namespace)::throw_for_encoding_error(char const*, char const*, unsigned long, unsigned long)':
example.cpp:(.text+0x1fd): undefined reference to `pqxx::argument_error::argument_error(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `main':
example.cpp:(.text+0x462): undefined reference to `pqxx::transaction_base::commit()'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `__static_initialization_and_destruction_0(int, int)':
example.cpp:(.text+0x600): undefined reference to `pqxx::internal::demangle_type_name[abi:cxx11](char const*)'
/usr/bin/ld: example.cpp:(.text+0x647): undefined reference to `pqxx::internal::demangle_type_name[abi:cxx11](char const*)'
/usr/bin/ld: example.cpp:(.text+0x68e): undefined reference to `pqxx::internal::demangle_type_name[abi:cxx11](char const*)'
/usr/bin/ld: example.cpp:(.text+0x6d5): undefined reference to `pqxx::internal::demangle_type_name[abi:cxx11](char const*)'
/usr/bin/ld: example.cpp:(.text+0x71c): undefined reference to `pqxx::internal::demangle_type_name[abi:cxx11](char const*)'
/usr/bin/ld: /tmp/ccW2W26H.o:example.cpp:(.text+0x763): more undefined references to `pqxx::internal::demangle_type_name[abi:cxx11](char const*)' follow
/usr/bin/ld: /tmp/ccW2W26H.o: in function `pqxx::check_version()':
example.cpp:(.text._ZN4pqxx13check_versionEv[_ZN4pqxx13check_versionEv]+0x31): undefined reference to `pqxx::internal::check_pqxx_version_7_9()'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `pqxx::string_traits<char const*>::into_buf(char*, char*, char const* const&)':
example.cpp:(.text._ZN4pqxx13string_traitsIPKcE8into_bufEPcS4_RKS2_[_ZN4pqxx13string_traitsIPKcE8into_bufEPcS4_RKS2_]+0xaa): undefined reference to `pqxx::conversion_overrun::conversion_overrun(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `pqxx::connection::connection(char const*)':
example.cpp:(.text._ZN4pqxx10connectionC2EPKc[_ZN4pqxx10connectionC5EPKc]+0x6b): undefined reference to `pqxx::connection::init(char const*)'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `pqxx::connection::~connection()':
example.cpp:(.text._ZN4pqxx10connectionD2Ev[_ZN4pqxx10connectionD5Ev]+0x18): undefined reference to `pqxx::connection::close()'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `pqxx::field::view() const &':
example.cpp:(.text._ZNKR4pqxx5field4viewEv[_ZNKR4pqxx5field4viewEv]+0x28): undefined reference to `pqxx::field::size() const'
/usr/bin/ld: example.cpp:(.text._ZNKR4pqxx5field4viewEv[_ZNKR4pqxx5field4viewEv]+0x37): undefined reference to `pqxx::field::c_str() const &'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `pqxx::transaction_base::exec1(pqxx::zview)':
example.cpp:(.text._ZN4pqxx16transaction_base5exec1ENS_5zviewE[_ZN4pqxx16transaction_base5exec1ENS_5zviewE]+0x5d): undefined reference to `pqxx::result::front() const'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `pqxx::transaction_base::exec_n(int, pqxx::zview)':
example.cpp:(.text._ZN4pqxx16transaction_base6exec_nEiNS_5zviewE[_ZN4pqxx16transaction_base6exec_nEiNS_5zviewE]+0x63): undefined reference to `pqxx::transaction_base::exec_n(int, pqxx::zview, std::basic_string_view<char, std::char_traits<char> >)'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > pqxx::internal::state_buffer_overrun<long, unsigned long>(long, unsigned long)':
example.cpp:(.text._ZN4pqxx8internal20state_buffer_overrunIlmEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEET_T0_[_ZN4pqxx8internal20state_buffer_overrunIlmEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEET_T0_]+0x3d): undefined reference to `pqxx::internal::state_buffer_overrun[abi:cxx11](int, int)'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `pqxx::transaction<(pqxx::isolation_level)0, (pqxx::write_policy)1>::transaction(pqxx::connection&)':
example.cpp:(.text._ZN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EEC2ERNS_10connectionE[_ZN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EEC5ERNS_10connectionE]+0x31): undefined reference to `pqxx::internal::basic_transaction::basic_transaction(pqxx::connection&, pqxx::zview)'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `pqxx::transaction<(pqxx::isolation_level)0, (pqxx::write_policy)1>::~transaction()':
example.cpp:(.text._ZN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EED2Ev[_ZN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EED5Ev]+0x26): undefined reference to `pqxx::transaction_base::close()'
/usr/bin/ld: example.cpp:(.text._ZN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EED2Ev[_ZN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EED5Ev]+0x32): undefined reference to `pqxx::internal::basic_transaction::~basic_transaction()'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `int pqxx::transaction_base::query_value<int>(pqxx::zview)':
example.cpp:(.text._ZN4pqxx16transaction_base11query_valueIiEET_NS_5zviewE[_ZN4pqxx16transaction_base11query_valueIiEET_NS_5zviewE]+0xca): undefined reference to `pqxx::usage_error::usage_error(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/usr/bin/ld: example.cpp:(.text._ZN4pqxx16transaction_base11query_valueIiEET_NS_5zviewE[_ZN4pqxx16transaction_base11query_valueIiEET_NS_5zviewE]+0x10d): undefined reference to `pqxx::row::operator[](int) const'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > pqxx::to_string<int>(int const&)':
example.cpp:(.text._ZN4pqxx9to_stringIiEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKT_[_ZN4pqxx9to_stringIiEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKT_]+0xa8): undefined reference to `pqxx::conversion_error::conversion_error(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/usr/bin/ld: example.cpp:(.text._ZN4pqxx9to_stringIiEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKT_[_ZN4pqxx9to_stringIiEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKT_]+0x164): undefined reference to `pqxx::internal::integral_traits<int>::into_buf(char*, char*, int const&)'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `void pqxx::internal::render_item<int>(int const&, char*&, char*)':
example.cpp:(.text._ZN4pqxx8internal11render_itemIiEEvRKT_RPcS5_[_ZN4pqxx8internal11render_itemIiEEvRKT_RPcS5_]+0x2e): undefined reference to `pqxx::internal::integral_traits<int>::into_buf(char*, char*, int const&)'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > pqxx::connection::quote<char*>(char* const&) const':
example.cpp:(.text._ZNK4pqxx10connection5quoteIPcEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKT_[_ZNK4pqxx10connection5quoteIPcEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKT_]+0x151): undefined reference to `pqxx::connection::esc_to_buf(std::basic_string_view<char, std::char_traits<char> >, char*) const'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `int pqxx::field::as<int>() const':
example.cpp:(.text._ZNK4pqxx5field2asIiEET_v[_ZNK4pqxx5field2asIiEET_v]+0x19): undefined reference to `pqxx::field::is_null() const'
/usr/bin/ld: example.cpp:(.text._ZNK4pqxx5field2asIiEET_v[_ZNK4pqxx5field2asIiEET_v]+0x2c): undefined reference to `pqxx::internal::throw_null_conversion(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > pqxx::to_string<char*>(char* const&)':
example.cpp:(.text._ZN4pqxx9to_stringIPcEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKT_[_ZN4pqxx9to_stringIPcEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKT_]+0xa8): undefined reference to `pqxx::conversion_error::conversion_error(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
/usr/bin/ld: /tmp/ccW2W26H.o: in function `int pqxx::from_string<int>(std::basic_string_view<char, std::char_traits<char> >)':
example.cpp:(.text._ZN4pqxx11from_stringIiEET_St17basic_string_viewIcSt11char_traitsIcEE[_ZN4pqxx11from_stringIiEET_St17basic_string_viewIcSt11char_traitsIcEE]+0x2c): undefined reference to `pqxx::internal::integral_traits<int>::from_string(std::basic_string_view<char, std::char_traits<char> >)'
/usr/bin/ld: /tmp/ccW2W26H.o:(.data.rel.ro._ZTVN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EEE[_ZTVN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EEE]+0x20): undefined reference to `pqxx::internal::basic_transaction::do_commit()'
/usr/bin/ld: /tmp/ccW2W26H.o:(.data.rel.ro._ZTVN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EEE[_ZTVN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EEE]+0x28): undefined reference to `pqxx::transaction_base::do_abort()'
/usr/bin/ld: /tmp/ccW2W26H.o:(.data.rel.ro._ZTIN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EEE[_ZTIN4pqxx11transactionILNS_15isolation_levelE0ELNS_12write_policyE1EEE]+0x10): undefined reference to `typeinfo for pqxx::internal::basic_transaction'
collect2: error: ld returned 1 exit status

[jtv]

@ldpl what compile options did you use for compiling libpqxx?

[jtv]

This appears to be a duplicate of #820 and #822, but we never got to the bottom of those. :-(

In this case though, your link options seem to be in the wrong order. You did -lpq -lpqxx but the proper order is -lpqxx -lpq.

[ldpl]

I tried compiling with no options, tried with ./configure --disable-shared as in documentation, tried different combinations like ./configure --enable-shared --prefix=/usr CXXFLAGS="-std=c++17", nothing makes any difference.
Swapping -lpqxx and -lpq changes nothing as well.

[jtv]

Thanks @ldpl, that tells us a few things about what the problem isn't. Unfortunately at this point we're left with a mystery, so we'll have to go through the possibilities.

Here's a very basic one: What happens if, on the command line where you compile & link your own application, you put the -lpqxx -lpq part after the name of your source file?

So: g++ example.cpp -lpq -lpqxx

[ldpl]

So: g++ example.cpp -lpq -lpqxx

No idea why but that compiles just fine.

UPD. And so does g++ -fPIC -shared -lpq -lpqxx example.cpp
UPD2. Actually, g++ example.cpp -lpqxx -lpq compiles, not g++ example.cpp -lpq -lpqxx

[tt4g]

This may be due to gcc's behavior.
I found a detailed explanation on Stack Overflow: https://stackoverflow.com/a/409402

[jtv]

Exactly. Thanks @tt4g for looking that up.

The surprising part is that AFAIR the linking of libraries with -l used to be done in a separate stage, after any source files and object files named on the command line were linked.

[jtv]

Well, then I think we know why this happens. I'll close this ticket, and add the note to the earlier instances of the same problem.

(Unfortunately I don't think I can prevent recurrences of this problem in the future, since the documentation already shows the correct order pretty clearly. Or did I miss a spot?)

[ldpl]

What I don't understand here is why -l defaults to static linking for pqxx that depends on -l order. Or, at least, that's what I see happening here.

[jtv]

It puzzles me too, @ldpl. AFAIK the convention has always been to write the linking command line with the object file(s) before the libraries, and perhaps the compiler's behaviour has changed for usage that does not follow that convention.

An optimisation perhaps... At least in libpqxx a lot of the build time is spent linking. And to make it worse it's a single-process step where it can be hard for build systems to find other useful work to do.