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c++postgresqllibpqxx

Did I install pqxx wrong?

I've just installed libpqxx (postgresql for c++). I was following this tutorial: http://www.tutorialspoint.com/postgresql/postgresql_c_cpp.htm Everything is Ok less one thing. When I tried to compile the example code I saw all these errors:

/home/JakisUzytkownik/Hobby/C++/DzialaNaUbuntu.o||In function `main':|
DzialaNaUbuntu.cpp|| undefined reference to `pqxx::connection_base::is_open() const'|
DzialaNaUbuntu.cpp|| undefined reference to `pqxx::connection_base::dbname()'|
DzialaNaUbuntu.cpp|| undefined reference to `pqxx::connection_base::disconnect()'|
/home/marcwel/Hobby/C++/DzialaNaUbuntu.o||In function `pqxx::connect_direct::connect_direct(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)':|
DzialaNaUbuntu.cpp:(.text._ZN4pqxx14connect_directC2ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE[_ZN4pqxx14connect_directC5ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE]+0x1f)||undefined reference to `pqxx::connectionpolicy::connectionpolicy(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'|
DzialaNaUbuntu.cpp:(.text._ZN4pqxx14connect_directC2ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE[_ZN4pqxx14connect_directC5ERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEE]+0x24)||undefined reference to `vtable for pqxx::connect_direct'|
/home/marcwel/Hobby/C++/DzialaNaUbuntu.o||In function `pqxx::connect_direct::~connect_direct()':|
DzialaNaUbuntu.cpp:(.text._ZN4pqxx14connect_directD2Ev[_ZN4pqxx14connect_directD5Ev]+0xd)||undefined reference to `vtable for pqxx::connect_direct'|
DzialaNaUbuntu.cpp:(.text._ZN4pqxx14connect_directD2Ev[_ZN4pqxx14connect_directD5Ev]+0x20)||undefined reference to `pqxx::connectionpolicy::~connectionpolicy()'|
/home/marcwel/Hobby/C++/DzialaNaUbuntu.o||In function `pqxx::basic_connection<pqxx::connect_direct>::basic_connection(char const*)':|
DzialaNaUbuntu.cpp:(.text._ZN4pqxx16basic_connectionINS_14connect_directEEC2EPKc[_ZN4pqxx16basic_connectionINS_14connect_directEEC5EPKc]+0x38)||undefined reference to `pqxx::connection_base::connection_base(pqxx::connectionpolicy&)'|
DzialaNaUbuntu.cpp:(.text._ZN4pqxx16basic_connectionINS_14connect_directEEC2EPKc[_ZN4pqxx16basic_connectionINS_14connect_directEEC5EPKc]+0xc3)||undefined reference to `pqxx::connection_base::init()'|
/home/marcwel/Hobby/C++/DzialaNaUbuntu.o||In function `pqxx::basic_connection<pqxx::connect_direct>::~basic_connection()':|
DzialaNaUbuntu.cpp:(.text._ZN4pqxx16basic_connectionINS_14connect_directEED2Ev[_ZN4pqxx16basic_connectionINS_14connect_directEED5Ev]+0x17)||undefined reference to `pqxx::connection_base::close()'|

IDE: CodeBlocks, OS: Ubuntu

Solution

  • 'undefined reference' error means that you didn't link the compiled code to the library as the program will need to use the library to run properly. You should be able to compile the code from the tutorial by linking the code to libpqxx and libpq;

    g++ your_code.cpp -lpqxx -lpq -o your-exec

    You might need to manually supply the path to the library by adding -L to your compilation command if it wasn't installed in the default system library, like so;

    g++ your_code.cpp -L../path-to-libpqxx -lpqxx -lpq -o your-exec

    But if indeed the library was installed in the right placee, then you might have to make sure the library is uploaded by the system by issuing sudo ldconfig command before linking it to your compiled code.

    To run the code successfully you would also need to make sure your postgresql database is running with the right access right and database table, but that's no longer a programming or compiling problem but administrative issue.

    Hope that helps.