CMake on Windows - missing linker symbols

[stalek71]

When I use work.exec_prepared1 method on linux it can be build without any problems. When I build the same project on Windows (using CMake with Microsoft Visual C++ 2019) it complains about missing symbols like below:

 error LNK2019: unresolved external symbol "public: static char * __cdecl pqxx::string_traits<signed char>::into_buf(char *,char *,signed char const &)"
 error LNK2019: unresolved external symbol "public: static unsigned __int64 __cdecl pqxx::string_traits<signed char>::size_buffer(signed char const &)"

Is it possible to fix it without waiting for a new version (by providing some template specializations)?

I tried to add something like below, but it didn't work. The message related to it is below the def...

template
unsigned __int64 __cdecl pqxx::string_traits<signed char>::size_buffer(signed char const &) noexcept;

pqxx/strconv.hxx(194): warning C4661: 'size_t pqxx::string_traits<signed char>::size_buffer(const TYPE &) noexcept': no suitable definition provided for explicit template instantiation request

[jtv]

There really isn't supposed to be a pqxx::string_traits<signed char>. The reason is that a signed char can reasonably mean either "a very small integer" or "a single-byte character." (Same for char and unsigned char by the way.)

So the real question is: what code is looking for that specialisation? Is it possible that you were passing an unsigned char parameter to the prepared statement?

[jtv]

Ahem. I meant: is it possible that you were passing a signed char to the prepared statement? Perhaps some standard type that one compiler typedefs to signed char but the other compiler treats as a separate type, or typedefs to a different one?

[stalek71]

This is a code fragment that causes the issue. The interesting fact is when I use inline value it needs five symbols instead of 2 (like in case of std::string var)...

int PostgresStorage::CreateSerie(const std::string &name, int8_t pointType) const
{
    // Start transaction
    pqxx::work work(*connPtr_);
    // auto CREATE_SERIE_STMT = "create_serie"; <- It's const char*
    auto row = work.exec_prepared1(CREATE_SERIE_STMT, name, pointType);
    //auto row = work.exec_prepared1(CREATE_SERIE_STMT, (unsigned char*)"", pointType);
    work.commit();

    return row[0].as<int>();
}

For uchar case it shows such symbols:

[build] TimeSeriesStorage.lib(PostgresStorage.cpp.obj) : error LNK2019: unresolved external symbol "public: static bool __cdecl pqxx::nullness<unsigned char *,void>::is_null(unsigned char * const &)" (?is_null@?$nullness@PEAEX@pqxx@@SA_NAEBQEAE@Z) referenced in function "bool __cdecl pqxx::is_null<unsigned char *>(unsigned char * const &)" (??$is_null@PEAE@pqxx@@YA_NAEBQEAE@Z)
[build] TimeSeriesStorage.lib(PostgresStorage.cpp.obj) : error LNK2019: unresolved external symbol "public: static char * __cdecl pqxx::string_traits<unsigned char *>::into_buf(char *,char *,unsigned char * const &)" (?into_buf@?$string_traits@PEAE@pqxx@@SAPEADPEAD0AEBQEAE@Z) referenced in function "class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > __cdecl pqxx::to_string<unsigned char *>(unsigned char * const &)" (??$to_string@PEAE@pqxx@@YA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AEBQEAE@Z)
[build] TimeSeriesStorage.lib(PostgresStorage.cpp.obj) : error LNK2019: unresolved external symbol "public: static unsigned __int64 __cdecl pqxx::string_traits<unsigned char *>::size_buffer(unsigned char * const &)" (?size_buffer@?$string_traits@PEAE@pqxx@@SA_KAEBQEAE@Z) referenced in function "unsigned __int64 __cdecl pqxx::size_buffer<unsigned char *>(unsigned char * const &)" (??$size_buffer@PEAE@pqxx@@YA_KAEBQEAE@Z)
[build] TimeSeriesStorage.lib(PostgresStorage.cpp.obj) : error LNK2019: unresolved external symbol "public: static char * __cdecl pqxx::string_traits<signed char>::into_buf(char *,char *,signed char const &)" (?into_buf@?$string_traits@C@pqxx@@SAPEADPEAD0AEBC@Z) referenced in function "class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > __cdecl pqxx::to_string<signed char>(signed char const &)" (??$to_string@C@pqxx@@YA?AV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@AEBC@Z)
[build] TimeSeriesStorage.lib(PostgresStorage.cpp.obj) : error LNK2019: unresolved external symbol "public: static unsigned __int64 __cdecl pqxx::string_traits<signed char>::size_buffer(signed char const &)" (?size_buffer@?$string_traits@C@pqxx@@SA_KAEBC@Z) referenced in function "unsigned __int64 __cdecl pqxx::size_buffer<signed char>(signed char const &)" (??$size_buffer@C@pqxx@@YA_KAEBC@Z)
[build] tests\Storage\TimeSeries\TimeSeriesStorageTests.exe : fatal error LNK1120: 5 unresolved externals

[stalek71]

I tried to build it on Arch linux (Manjaro) also and it fails as well.
I have no baseline set for vcpkg so it uses the latest version of libpqxx (7.6)

[build] Starting build
[proc] Executing command: /usr/bin/cmake --build /home/alek/Projects/mesh.saas/out/build/linux-base
[build] [1/3] Linking CXX executable tests/Storage/TimeSeries/TimeSeriesStorageTests
[build] FAILED: tests/Storage/TimeSeries/TimeSeriesStorageTests 
[build] : && /usr/bin/g++ -g  tests/Storage/TimeSeries/CMakeFiles/TimeSeriesStorageTests.dir/Source/main.cpp.o tests/Storage/TimeSeries/CMakeFiles/TimeSeriesStorageTests.dir/Source/TimeSeriesStorageTests.cpp.o -o tests/Storage/TimeSeries/TimeSeriesStorageTests  src/Libraries/Common/libCommon.a  src/Libraries/Storage/TimeSeries/libTimeSeriesStorage.a  vcpkg_installed/x64-linux/debug/lib/libgtestd.a  vcpkg_installed/x64-linux/debug/lib/libgmockd.a  vcpkg_installed/x64-linux/debug/lib/libpqxx-7.6.a  vcpkg_installed/x64-linux/debug/lib/libpq.a  vcpkg_installed/x64-linux/debug/lib/libpq.a  vcpkg_installed/x64-linux/debug/lib/libpgport.a  vcpkg_installed/x64-linux/debug/lib/libpgcommon.a  vcpkg_installed/x64-linux/debug/lib/libssl.a  vcpkg_installed/x64-linux/debug/lib/libcrypto.a  -ldl  vcpkg_installed/x64-linux/debug/lib/libgtestd.a  -lpthread && :
[build] /usr/bin/ld: src/Libraries/Storage/TimeSeries/libTimeSeriesStorage.a(PostgresStorage.cpp.o): in function `std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > pqxx::to_string<signed char>(signed char const&)':
[build] /home/alek/Projects/mesh.saas/out/build/linux-base/vcpkg_installed/x64-linux/include/pqxx/internal/conversions.hxx:1100: undefined reference to `pqxx::string_traits<signed char>::into_buf(char*, char*, signed char const&)'
[build] /usr/bin/ld: src/Libraries/Storage/TimeSeries/libTimeSeriesStorage.a(PostgresStorage.cpp.o): in function `unsigned long pqxx::size_buffer<signed char>(signed char const&)':
[build] /home/alek/Projects/mesh.saas/out/build/linux-base/vcpkg_installed/x64-linux/include/pqxx/strconv.hxx:370: undefined reference to `pqxx::string_traits<signed char>::size_buffer(signed char const&)'
[build] collect2: error: ld returned 1 exit status
[build] [2/3] Linking CXX executable src/Services/CalculationSvc/CalculationSvc
[build] [3/3] Linking CXX executable src/Services/Storage/TimeSeriesStorageSvc/TimeSeriesStorageSvc
[build] ninja: build stopped: subcommand failed.
[build] Build finished with exit code 1

vcpkg config has no any special deps:

{
  "name": "mesh",
  "version-string": "0.0.1",
  "dependencies": [
    "gtest",
    "grpc",
    "protobuf",
    "openssl",
    "libpq",
    "libpqxx"
  ],
  "overrides": [
  ]
}

I was building it using g++ in version 11.1.0. Build options are like below (tested also with 17 and exts):

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

[jtv]

So yes, standard type that gets typedef'ed to signed char. In this case, int8_t. Try widening pointType to, say, short:

auto row = work.exec_prepared1(CREATE_SERIE_STMT, name, short(pointType));

[stalek71]

I was able to build it on Linux as well as on Windows also. I will check docker image yet (two stage build based on alpine/musl), but it should be ok also... Thanks for the hint!
Btw: why it doesn't work with signed char as a param?

[jtv]

Good question! The problem with signed/unsigned char is that it's open to two very different interpretations: "a character" or "a small integer." That ambiguity is, I think, trouble waiting to happen. When you convert it to a string, should it come out as text, or as a number? Bear in mind that for various reasons, existing codebases sometimes use signed char or unsigned char for bytes in a string.

If you'd asked me 20 years ago whether signed char should come out as text or as a number, I would probably have said "it makes a bit more sense to treat it as text." But I wasn't certain enough to build that choice into libpqxx. And today I'm glad, because int8_t is clearly an integer, and your compiler implements it as a signed char.

It's probably worth building in a trick to make this situation produce a more helpful error message.

[stalek71]

Yes, it's a bit problematic. Probably some trait should be added to spec yet as char type is treated as num here instead of "character based data class":
https://en.cppreference.com/w/cpp/types/is_integral

[jtv]

In any case... did the short(...) help?

[stalek71]

Yes, thanks. It resolved the issue.

[jtv]

I'll merge a fix for a better error message, and that will automatically close this ticket. Thanks for reporting.