undefined reference to `check(std::string const&)' while linking

Question

I have some "simple" code in C++ to connect to a MySQL database (which is localhost, btw).

#include <stdlib.h>
#include <iostream>
#include "mysql/include/mysql/jdbc.h"


using namespace sql;


int main() {

  std::cout << "Test"<< std::endl;

  try {
   sql::Driver *myDriver;
   sql::Connection *myConn;
   sql::Statement *myStmt;
   sql::ResultSet *myRes;

   myDriver = sql::mysql::get_mysql_driver_instance();
   myConn = myDriver ->connect("tcp://127.0.0.1", "root", "");
   myConn->setSchema("root");

   myStmt = myConn->createStatement();
   myRes = myStmt->executeQuery("SELECT 'Hello World' AS _message");

   while (myRes->next()) {
     std::cout << myRes->getString("_message") << std::endl;
   }
   delete myRes;
   delete myStmt;
   delete myConn;

 } catch (sql::SQLException &e) {
   std::cout << "Filed connect to Database" << std::endl;
   std::cout << "Error: " << e.what() << std::endl;
   std::cout << "Error code: " << e.getErrorCode() << std::endl;
 }
}

The file jdbc.h is just a lot of different #include for header files.

I use 2 commands to compile: g++ -c -Wall -I/usr/include/cppconn connect.cpp -o connect.o and g++ -lm -L/usr/lib/x86_64-linux-gnu -lmysqlcppconn connect.o -o connect

Which produced this linking error:

/usr/bin/ld: connect.o: in function "check_lib()':
connect.cpp:(.text+0x2c): undefined reference to `check(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)"
/usr/bin/ld: connect.cpp:(.text+0x77): undefined reference to "check(std::map<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::less<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > >, std::allocator<std::pair<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > > const&)"
/usr/bin/ld: connect.o: in function `sql::mysql::get_driver_instance_by_name(char const*)':
connect.cpp:(.text+0xfa): undefined reference to   "sql::mysql::_get_driver_instance_by_name(char const*)"
collect2: error: ld returned 1 exit status

Which I kinda resolved using this answer: https://stackoverflow.com/a/33395489/14814564 , essentially by putting #define _GLIBCXX_USE_CXX11_ABI 0 at the top of the file, which after compilation, produces this linking error:

/usr/bin/ld: connect.o: in function "check_lib()':
connect.cpp:(.text+0x2c): undefined reference to "check(std::string const&)'
/usr/bin/ld: connect.cpp:(.text+0x77): undefined reference to "check(std::map<std::string, std::string, std::less<std::string>, std::allocator<std::pair<std::string const, std::string> > > const&)'
/usr/bin/ld: connect.o: in function `sql::mysql::get_driver_instance_by_name(char const*)':
connect.cpp:(.text+0xfa): undefined reference to "sql::mysql::_get_driver_instance_by_name(char const*)'
collect2: error: ld returned 1 exit status

Why does this linking error keep popping up and how do I resolve it?

You're not linking something, that needs to be linked against. This error is avoidable by using cmake's find_package and link_libraries for example. I strongly recommend to not command line your compiling/linking manually (at least for projects which consist of more than 1 source file or use more than zero 3rd party libraries). — nada, Aug 11 '21 at 08:46
@nada I will check cmake out. Yeah, I don't always compile through my terminal, I just did for now because I wanna have a taste of how the program is compiled. Why did you recommend I use those functions exactly? — Kostas M, Aug 11 '21 at 09:01
Because if you wanna use MySQL in your C++ project with CMake you would simply do `find_package(MySQL)` and `target_link_library(your_project_name ${MYSQL_LIBRARY})`. It's as easy as that. — nada, Aug 11 '21 at 09:18
Are you sure `-lmysqlcppconn` locates at the path `/usr/lib/x86_64-linux-gnu` ?? — nhatnq, Aug 11 '21 at 09:47
Tbh @nhatnq, I don't know. I just found the commands online, from a Youtube tutorial and copied them. Do you know of any ways to check that `-lmysqlcppconn` is in the path `/usr/lib/x86_64-linux-gun/`?? — Kostas M, Aug 11 '21 at 10:34
@KostasM That's why it does not always work well when you try something You need to get better. The linker will try to find the `libmysqlcppconn.so` in the library search path specified by `-L` as well as in the standard paths — nhatnq, Aug 11 '21 at 10:43
@nhatnq Sorry for the late response. I just checked the `usr/lib/x86_64-linux-gnu` path, and there are a `libmysqlconn.so` as well as a `libmysqlconn.so.7`, a `libmysqlconn.so.7.1.1.12` and a `libmysqlconn.a` library. Do you think I should link another library? Or do you reckon the linking error is somewhere else? — Kostas M, Aug 12 '21 at 08:45
Are you suggesting I change the file name in the folder or change the linking command? didn't quite catch that, unfortunately — Kostas M, Aug 12 '21 at 09:54

undefined reference to `check(std::string const&)' while linking

0 Answers0