Compile error - error: invalid use of ‘this’ at top level

[nairary]

Trying to compile code with this lib on manjaro linux with g++ 8.5.0 and astra linux with g++ 8.6.0 have same error on both, can't use higher g++

[jtv]

I think gcc 8 can work, but you'll have to set the C++ version. Those gcc versions default to a C++ version that's too told for current libpqxx versions, but you can select a newer version.

Try adding -std=c++17 to your compile versions. (Or soon you will need -std=c++20 as a minimum.)

If you're using the configure script, add CXXFLAGS='-std=c++17' to the configure command line (you can add other compiler options in there as well). If you're using CMake, I believe you need to add -DCMAKE_CXX_FLAGS='-std=c++17' to the cmake command line, with the same notes.

[nairary]

I'm already using this flag.
This is my compilation line: g++-8 -o name -std=c++17 *.cpp -lssh -pthread -lstdc++fs -lpq -lpqxx

[nairary]

That's what I get

In file included from /usr/local/include/pqxx/pqxx:17,
from PSQLConnector.h:5,
from PSQLConnector.cpp:1:
/usr/local/include/pqxx/range.hxx:143:24: error: invalid use of ‘this’ at top level
noexcept(noexcept(*this->value() == *rhs.value()))
^~~~
/usr/local/include/pqxx/range.hxx:154:24: error: invalid use of ‘this’ at top level
noexcept(noexcept(*this == rhs))
^~~~
/usr/local/include/pqxx/range.hxx:266:23: error: invalid use of ‘this’ at top level
noexcept(noexcept(this->lower_bound() == rhs.lower_bound()) and noexcept(
^~~~
/usr/local/include/pqxx/range.hxx:267:7: error: invalid use of ‘this’ at top level
this->upper_bound() == rhs.upper_bound()) and noexcept(this->empty()))
^~~~
/usr/local/include/pqxx/range.hxx:267:62: error: invalid use of ‘this’ at top level
this->upper_bound() == rhs.upper_bound()) and noexcept(this->empty()))
^~~~
/usr/local/include/pqxx/range.hxx:275:24: error: invalid use of ‘this’ at top level
noexcept(noexcept(*this == rhs))
^~~~
/usr/local/include/pqxx/range.hxx:315:25: error: invalid use of ‘this’ at top level
noexcept(noexcept((*this & other) == other))
^~~~
In file included from /usr/local/include/pqxx/pqxx:17,
from PSQLConnector.h:5,
from ssh_connector.h:4,
from ssh_connector.cpp:1:
/usr/local/include/pqxx/range.hxx:143:24: error: invalid use of ‘this’ at top level
noexcept(noexcept(*this->value() == *rhs.value()))
^~~~
/usr/local/include/pqxx/range.hxx:154:24: error: invalid use of ‘this’ at top level
noexcept(noexcept(*this == rhs))
^~~~
/usr/local/include/pqxx/range.hxx:266:23: error: invalid use of ‘this’ at top level
noexcept(noexcept(this->lower_bound() == rhs.lower_bound()) and noexcept(
^~~~
/usr/local/include/pqxx/range.hxx:267:7: error: invalid use of ‘this’ at top level
this->upper_bound() == rhs.upper_bound()) and noexcept(this->empty()))
^~~~
/usr/local/include/pqxx/range.hxx:267:62: error: invalid use of ‘this’ at top level
this->upper_bound() == rhs.upper_bound()) and noexcept(this->empty()))
^~~~
/usr/local/include/pqxx/range.hxx:275:24: error: invalid use of ‘this’ at top level
noexcept(noexcept(*this == rhs))
^~~~
/usr/local/include/pqxx/range.hxx:315:25: error: invalid use of ‘this’ at top level
noexcept(noexcept((*this & other) == other))

[nairary]

Built g++-9 from source package.
Compile with g++-9 -o name -std=c++17 *.cpp -lssh -pthread -lstdc++fs -lpq -lpqxx
Got a lot of undefined references to std::to_chars(char*, char*, float) and std::from_chars(char const*, char const*, float&, std::chars_format)

/usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): in function «long double (anonymous namespace)::from_string_arithmetic(std::basic_string_view<char, std::char_traits >)»:
/home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:289:(.text._ZN12_GLOBAL__N_122from_string_arithmeticIeEET_St17basic_string_viewIcSt11char_traitsIcEE[_ZN4pqxx8internal12float_traitsIeE11from_stringESt17basic_string_viewIcSt11char_traitsIcEE]+0x68): undefined reference to std::from_chars(char const*, char const*, long double&, std::chars_format)' /usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): in function «double (anonymous namespace)::from_string_arithmetic<double>(std::basic_string_view<char, std::char_traits<char> >)»: /home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:289:(.text._ZN12_GLOBAL__N_122from_string_arithmeticIdEET_St17basic_string_viewIcSt11char_traitsIcEE[_ZN4pqxx8internal12float_traitsIdE11from_stringESt17basic_string_viewIcSt11char_traitsIcEE]+0x6b): undefined reference to std::from_chars(char const*, char const*, double&, std::chars_format)'
/usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): in function «float (anonymous namespace)::from_string_arithmetic(std::basic_string_view<char, std::char_traits >)»:
/home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:289:(.text._ZN12_GLOBAL__N_122from_string_arithmeticIfEET_St17basic_string_viewIcSt11char_traitsIcEE[_ZN4pqxx8internal12float_traitsIfE11from_stringESt17basic_string_viewIcSt11char_traitsIcEE]+0x6a): undefined reference to std::from_chars(char const*, char const*, float&, std::chars_format)' /usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): in function «std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > pqxx::internal::to_string_float<long double>(long double)»: /home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:131:(.text._ZN4pqxx8internal15to_string_floatIeEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEET_[_ZN4pqxx8internal15to_string_floatIeEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEET_]+0x6e): undefined reference to std::to_chars(char*, char*, long double)'
/usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): в функции «std::__cxx11::basic_string<char, std::char_traits, std::allocator > pqxx::internal::to_string_float(double)»:
/home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:131:(.text.ZN4pqxx8internal15to_string_floatIdEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEET[ZN4pqxx8internal15to_string_floatIdEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEET]+0x6a): undefined reference to std::to_chars(char*, char*, double)' /usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): in function «std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > pqxx::internal::to_string_float<float>(float)»: /home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:131:(.text._ZN4pqxx8internal15to_string_floatIfEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEET_[_ZN4pqxx8internal15to_string_floatIfEENSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEET_]+0x6a): undefined reference to std::to_chars(char*, char*, float)'
/usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): in function «pqxx::internal::float_traits::into_buf(char*, char*, float const&)»:
/home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:131:(.text._ZN4pqxx8internal12float_traitsIfE8into_bufEPcS3_RKf[_ZN4pqxx8internal12float_traitsIfE8into_bufEPcS3_RKf]+0x33): undefined reference to std::to_chars(char*, char*, float)' /usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): in function «pqxx::internal::float_traits<double>::into_buf(char*, char*, double const&)»: /home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:131:(.text._ZN4pqxx8internal12float_traitsIdE8into_bufEPcS3_RKd[_ZN4pqxx8internal12float_traitsIdE8into_bufEPcS3_RKd]+0x33): undefined reference to std::to_chars(char*, char*, double)'
/usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): in function «pqxx::internal::float_traits::into_buf(char*, char*, long double const&)»:
/home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:131:(.text._ZN4pqxx8internal12float_traitsIeE8into_bufEPcS3_RKe[_ZN4pqxx8internal12float_traitsIeE8into_bufEPcS3_RKe]+0x34): undefined reference to std::to_chars(char*, char*, long double)' /usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): in function «pqxx::internal::float_traits<float>::to_buf(char*, char*, float const&)»: /home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:131:(.text._ZN4pqxx8internal12float_traitsIfE6to_bufEPcS3_RKf[_ZN4pqxx8internal12float_traitsIfE6to_bufEPcS3_RKf]+0x33): undefined reference to std::to_chars(char*, char*, float)'
/usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): in function «pqxx::internal::float_traits::to_buf(char*, char*, double const&)»:
/home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:131:(.text._ZN4pqxx8internal12float_traitsIdE6to_bufEPcS3_RKd[_ZN4pqxx8internal12float_traitsIdE6to_bufEPcS3_RKd]+0x33): undefined reference to std::to_chars(char*, char*, double)' /usr/bin/ld: /usr/local/lib/libpqxx.a(strconv.o): in function «pqxx::internal::float_traits<long double>::to_buf(char*, char*, long double const&)»: /home/aleksandr/DEV/libpqxx-7.8.1/src/strconv.cxx:131:(.text._ZN4pqxx8internal12float_traitsIeE6to_bufEPcS3_RKe[_ZN4pqxx8internal12float_traitsIeE6to_bufEPcS3_RKe]+0x34): undefined reference to std::to_chars(char*, char*, long double)'

[tt4g]

The error message "invalid use of 'this' at top level" is probably a bug in gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52869

I think the reason the error occurs when compiling by gcc 9 is that installed libpqxx is not compiled by gcc 9.
If you have built and installed libpqxx yourself, re-install it.

[nairary]

checking whether we need a link option for <filesystem> support... configure: error: There seems to be <filesystem> support, but I could not figure out now to make it work. You'll have to add set your own build options for this.
Now I'm getting this error, while trying to re-install library with
./configure CXX=gcc-9 CXXFLAGS="-lstdc++fs -std=c++17"
EDIT:
./configure CXX=gcc-9 CXXFLAGS="-std=c++17 -lstdc++fs" LDFLAGS=-L/usr/lib/gcc/x86_64-pc-linux-gnu/9.5.0/include/c++/filesystem
Trying to manually specify the library location does not help

[tt4g]

Since gcc is C compiler, C++ compiler is g++, you are trying to build C++ source code with a C compiler.
That will never work.

And -lstdc++fs option is not required for GCC 9.

[jtv]

Right - it may be possible to build C++ by calling "gcc", since gcc was originally a wrapper for various compilers, but you'd need a bunch of extra options and the simple solution is to call "g++" instead.

In addition to this, I don't think -lstdc++fs belongs in CXXFLAGS. I think it belongs in either LOADLIBES or LDFLAGS.

[jtv]

@nairary, did using g++-9 instead of gcc-9 fix it?

[nairary]

Sorry for taking so long to respond, was busy.
Yes, if configured for g++-9 , then everything will work.
Unfortunately I need to use gcc8 and in the end I decided to switch to libp with C, but thanks for the help!