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error: undefined reference to `mysql_init'

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  • J jsulm
    4 Jan 2024, 06:56

    @micha_eleric Why don't you simply try?
    It does not matter where in the pro file you add it.

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    micha_eleric
    wrote on 4 Jan 2024, 07:03 last edited by
    #9

    @jsulm :-1: error: cannot find -lmysql: No such file or directory

    C 1 Reply Last reply 4 Jan 2024, 07:06
    0
    • M micha_eleric
      4 Jan 2024, 07:03

      @jsulm :-1: error: cannot find -lmysql: No such file or directory

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      Christian Ehrlicher
      Lifetime Qt Champion
      wrote on 4 Jan 2024, 07:06 last edited by
      #10

      @micha_eleric Then you should pass the correct path where the mysql library resides in.

      Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
      Visit the Qt Academy at https://academy.qt.io/catalog

      M 1 Reply Last reply 4 Jan 2024, 07:11
      0
      • J jsulm
        4 Jan 2024, 06:56

        @micha_eleric Why don't you simply try?
        It does not matter where in the pro file you add it.

        M Offline
        M Offline
        micha_eleric
        wrote on 4 Jan 2024, 07:08 last edited by
        #11

        @jsulm lol, even tried

        unix:LIBS += -L/usr/lib -lmysql
        

        and

        unix:LIBS += -L/usr/lib/mysql
        

        of course it did not work, nor did i think it would, but it was a guess out of complete ignorance.

        1 Reply Last reply
        0
        • C Christian Ehrlicher
          4 Jan 2024, 07:06

          @micha_eleric Then you should pass the correct path where the mysql library resides in.

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          micha_eleric
          wrote on 4 Jan 2024, 07:11 last edited by
          #12

          @Christian-Ehrlicher path has plugin, plugins, and private folders.
          i know what the header files are called, no clue what the library files are called, so dont know what to look for.

          C 1 Reply Last reply 4 Jan 2024, 07:12
          0
          • M micha_eleric
            4 Jan 2024, 07:11

            @Christian-Ehrlicher path has plugin, plugins, and private folders.
            i know what the header files are called, no clue what the library files are called, so dont know what to look for.

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            Christian Ehrlicher
            Lifetime Qt Champion
            wrote on 4 Jan 2024, 07:12 last edited by
            #13

            It must be something like libmysql.so

            Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
            Visit the Qt Academy at https://academy.qt.io/catalog

            M 3 Replies Last reply 4 Jan 2024, 07:22
            1
            • C Christian Ehrlicher
              4 Jan 2024, 07:12

              It must be something like libmysql.so

              M Offline
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              micha_eleric
              wrote on 4 Jan 2024, 07:22 last edited by
              #14

              @Christian-Ehrlicher closest i find is libmysqlclient.so

              1 Reply Last reply
              0
              • C Christian Ehrlicher
                4 Jan 2024, 07:12

                It must be something like libmysql.so

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                micha_eleric
                wrote on 4 Jan 2024, 07:41 last edited by
                #15

                @Christian-Ehrlicher said in error: undefined reference to `mysql_init':

                It must be something like libmysql.so

                when i search install libmysql.so, it give links to install libmysqlclient, which i already installed.

                C 1 Reply Last reply 4 Jan 2024, 07:47
                0
                • M micha_eleric
                  4 Jan 2024, 07:41

                  @Christian-Ehrlicher said in error: undefined reference to `mysql_init':

                  It must be something like libmysql.so

                  when i search install libmysql.so, it give links to install libmysqlclient, which i already installed.

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                  Christian Ehrlicher
                  Lifetime Qt Champion
                  wrote on 4 Jan 2024, 07:47 last edited by
                  #16

                  @micha_eleric So why don't you try it out?

                  Qt Online Installer direct download: https://download.qt.io/official_releases/online_installers/
                  Visit the Qt Academy at https://academy.qt.io/catalog

                  S M 3 Replies Last reply 4 Jan 2024, 09:19
                  0
                  • C Christian Ehrlicher
                    4 Jan 2024, 07:47

                    @micha_eleric So why don't you try it out?

                    S Offline
                    S Offline
                    SGaist
                    Lifetime Qt Champion
                    wrote on 4 Jan 2024, 09:19 last edited by
                    #17

                    Hi,

                    When you want to use a library as you do, you need to install the corresponding dev package.

                    Interested in AI ? www.idiap.ch
                    Please read the Qt Code of Conduct - https://forum.qt.io/topic/113070/qt-code-of-conduct

                    M 1 Reply Last reply 4 Jan 2024, 21:14
                    0
                    • M micha_eleric
                      4 Jan 2024, 05:05

                      trying to understand how to use database, search for database gave mysql, search for mysql example gave https://www.codeguru.com/database/database-programming-with-c-c/

                      finally got mysql libraries installed.

                      .pro

                      QT += core gui
                      QT += sql
                      
                      greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
                      
                      CONFIG += c++11
                      
                      # You can make your code fail to compile if it uses deprecated APIs.
                      # In order to do so, uncomment the following line.
                      #DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0
                      INCLUDEPATH += /usr/include/mysql/
                      
                      SOURCES += \
                      CBankAccount.cpp \
                      CBankTransaction.cpp \
                      main.cpp \
                      CMainWindow.cpp
                      
                      HEADERS += \
                      CBankAccount.h \
                      CBankTransaction.h \
                      CMainQindow.h
                      
                      FORMS += \
                      database.ui
                      
                      # Default rules for deployment.
                      qnx: target.path = /tmp/$${TARGET}/bin
                      else: unix:!android: target.path = /opt/$${TARGET}/bin
                      !isEmpty(target.path): INSTALLS += target
                      

                      CBankTransaction.h

                      #ifndef CBANKTRANSACTION_H
                      #define CBANKTRANSACTION_H
                      
                      #include "CBankAccount.h"
                      #include <string>
                      
                      class CBankTransaction
                      {
                      private:
                         MYSQL* db_conn;
                      
                      public:
                          CBankTransaction(const std::string HOST, const std::string USER,
                                           const std::string PASSWORD, const std::string DATABASE);
                      };
                      
                      #endif // CBANKTRANSACTION_H
                      

                      CBankTransaction.cpp

                      #include "CBankTransaction.h"
                      
                      CBankTransaction::CBankTransaction(const std::string HOST, const std::string USER,
                                                         const std::string PASSWORD,
                                                         const std::string DATABASE)
                      {
                          db_conn = mysql_init(NULL);
                          db_conn = mysql_real_connect(db_conn, HOST.c_str(), USER.c_str(),
                                                       PASSWORD.c_str(), DATABASE.c_str(), 0, NULL, 0);
                      }
                      

                      error

                      error: undefined reference to `mysql_init'
                      undefined reference to `mysql_real_connect'
                      

                      what i have tried:
                      added "QT += sql", no change.
                      removed "#include <mysql.h>" from "CBankTransaction.h", because
                      "CBankAccount.h" already had it, no change.

                      someone said to a similar question, "The error is telling you that you haven't added the MySQL libs to your link-line.", but i have no clue about linker in qt creator. modify pro file, make file is auto generated, linker file? linker options?

                      from general undefined reference search, function not defined was an option, but mysql is a library, so function should be defined. i can find the .h file, but dont know what file the compiler is linking.

                      error is in the constructor. am i missing something in my code?
                      is it possible that library is not properly installed?

                      J Offline
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                      JonB
                      wrote on 4 Jan 2024, 09:20 last edited by JonB 1 Apr 2024, 09:58
                      #18

                      @micha_eleric
                      I wonder if you should take a step back and question why you are even trying to do this? You have chosen to pick example code from 2016, and one that has nothing to do with Qt. It uses direct, "low level" libraries to interact with MYSQL. But Qt provides a whole set of "higher level" classes, QSql..., which are integrated with Qt (e.g. can be used for models for Qt's views) and preferable in a host of ways.

                      Why don't you abandon that example's approach and just use the Qt way? My understanding is that if you are Windows you may have to(?) compile the MySQL libraries, but if you are Linux like I am your distro (e.g. Ubuntu) will offer a pre-compiled set of libraries for MySQL. My system does not have any libmysql.so files, the only stuff is libmysqlclient.... That is the route I would follow.

                      M 1 Reply Last reply 4 Jan 2024, 21:49
                      2
                      • C Christian Ehrlicher
                        4 Jan 2024, 07:47

                        @micha_eleric So why don't you try it out?

                        M Offline
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                        micha_eleric
                        wrote on 4 Jan 2024, 21:10 last edited by
                        #19

                        @Christian-Ehrlicher said in error: undefined reference to `mysql_init':

                        @micha_eleric So why don't you try it out?

                        i did. even different ways.

                        1 Reply Last reply
                        0
                        • S SGaist
                          4 Jan 2024, 09:19

                          Hi,

                          When you want to use a library as you do, you need to install the corresponding dev package.

                          M Offline
                          M Offline
                          micha_eleric
                          wrote on 4 Jan 2024, 21:14 last edited by
                          #20

                          @SGaist said in error: undefined reference to `mysql_init':

                          Hi,

                          When you want to use a library as you do, you need to install the corresponding dev package.

                          back tracking installs
                          [9th] sudo apt install mariadb-client-core-10.6
                          [8th] sudo apt install mysql-client-core-8.0
                          [7th] sudo apt-get install pike7.8-mysql
                          [6th] sudo apt-get install libmariadb-dev
                          [5th] sudo apt-get install libmariadb-dev-compat
                          [4th] sudo apt-get install libmariadbclient-dev [i think this is what moved mysql.h to new location, which caused previous .pro to need to be changed]
                          [3rd] sudo apt-get install libmysqlclient-dev
                          [2nd] sudo apt-get install mysql-shell
                          [1st] sudo dpkg-reconfigure libdvd-pkg

                          1 Reply Last reply
                          0
                          • C Christian Ehrlicher
                            4 Jan 2024, 07:47

                            @micha_eleric So why don't you try it out?

                            M Offline
                            M Offline
                            micha_eleric
                            wrote on 4 Jan 2024, 21:42 last edited by micha_eleric 1 May 2024, 02:34
                            #21

                            @Christian-Ehrlicher
                            [expected to need lmysql]
                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu -lmysql
                            :-1: error: cannot find -lmysql: No such file or directory

                            [maybe llibmysqlclient instead of lmysql]
                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu -llibmysqlclient
                            :-1: error: cannot find -llibmysqlclient: No such file or directory

                            [maybe l and lib are the same, as in lmath instead of libmath]
                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu -libmysqlclient
                            :-1: error: cannot find -libmysqlclient: No such file or directory

                            [did not expect it to work, but why not try and see?]
                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu
                            error: undefined reference to mysql_init' undefined reference to mysql_real_connect'

                            i will keep guessing

                            :-1: error: note to link with /usr/lib/x86_64-linux-gnu/libmysqlclient.a use -l:libmysqlclient.a or rename it to liblibmysqlclient.a
                            does not seem to be what https://doc.qt.io/qt-6/qmake-variable-reference.html#libs, says, but why not try?

                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu -l:libmysqlclient
                            :-1: error: cannot find -l:libmysqlclient: No such file or directory

                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu -liblibmysqlclient
                            :-1: error: cannot find -liblibmysqlclient: No such file or directory

                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu -l:libmysqlclient.a
                            298 errors in lib

                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu -liblibmysqlclient.a
                            :-1: error: cannot find -liblibmysqlclient.a: No such file or directory

                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu -libmysqlclient.a
                            :-1: error: cannot find -libmysqlclient.a: No such file or directory

                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu -libmysqlclient.so
                            :-1: error: cannot find -libmysqlclient.so: No such file or directory

                            unix:LIBS += -L/usr/lib -libmysqlclient
                            :-1: error: cannot find -libmysqlclient: No such file or directory

                            unix:LIBS += -L/usr/lib/ -libmysqlclient
                            :-1: error: cannot find -libmysqlclient: No such file or directory

                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu -l;libmysqlclient
                            [error, but disappears and can not copy]

                            unix:LIBS += -L/usr/lib/x86_64-linux-gnu -l libmysqlclient
                            :-1: error: cannot find -llibmysqlclient: No such file or directory

                            just to see what would happen
                            unix:LIBS += -L/usr/lib/ -llibmysqlclient
                            :-1: error: cannot find -llibmysqlclient: No such file or directory
                            :-1: error: note to link with
                            /usr/lib/gcc/x86_64-linux-gnu/11/../../../x86_64-linux-gnu/libmysqlclient.a use
                            -l:libmysqlclient.a or rename it to liblibmysqlclient.a

                            unix:LIBS += -L/usr/lib -llibmysqlclient
                            :-1: error: cannot find -llibmysqlclient: No such file or directory
                            :-1: error: note to link with
                            /usr/lib/gcc/x86_64-linux-gnu/11/../../../x86_64-linux-gnu/libmysqlclient.a use
                            -l:libmysqlclient.a or rename it to liblibmysqlclient.a

                            unix:LIBS += -L/usr/ -llibmysqlclient
                            :-1: error: cannot find -llibmysqlclient: No such file or directory
                            :-1: error: note to link with
                            /usr/lib/gcc/x86_64-linux-gnu/11/../../../x86_64-linux-gnu/libmysqlclient.a use
                            -l:libmysqlclient.a or rename it to liblibmysqlclient.a

                            unix:LIBS += -L/ -llibmysqlclient
                            :-1: error: cannot find -llibmysqlclient: No such file or directory
                            :-1: error: note to link with
                            /usr/lib/gcc/x86_64-linux-gnu/11/../../../x86_64-linux-gnu/libmysqlclient.a use
                            -l:libmysqlclient.a or rename it to liblibmysqlclient.a

                            unix:LIBS += -L -llibmysqlclient
                            error: undefined reference to mysql_init' undefined reference to mysql_real_connect'

                            1 Reply Last reply
                            0
                            • J JonB
                              4 Jan 2024, 09:20

                              @micha_eleric
                              I wonder if you should take a step back and question why you are even trying to do this? You have chosen to pick example code from 2016, and one that has nothing to do with Qt. It uses direct, "low level" libraries to interact with MYSQL. But Qt provides a whole set of "higher level" classes, QSql..., which are integrated with Qt (e.g. can be used for models for Qt's views) and preferable in a host of ways.

                              Why don't you abandon that example's approach and just use the Qt way? My understanding is that if you are Windows you may have to(?) compile the MySQL libraries, but if you are Linux like I am your distro (e.g. Ubuntu) will offer a pre-compiled set of libraries for MySQL. My system does not have any libmysql.so files, the only stuff is libmysqlclient.... That is the route I would follow.

                              M Offline
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                              micha_eleric
                              wrote on 4 Jan 2024, 21:49 last edited by micha_eleric 1 Apr 2024, 21:49
                              #22

                              @JonB said in error: undefined reference to `mysql_init':

                              @micha_eleric
                              I wonder if you should take a step back and question why you are even trying to do this?

                              first example found, first example try

                              You have chosen to pick example code from 2016

                              does it matter if it is from 2016, or 1908, it showed what library is needed, and how to link libraries, which will be needed for future projects.

                              J 1 Reply Last reply 5 Jan 2024, 08:29
                              0
                              • C Christian Ehrlicher
                                4 Jan 2024, 07:12

                                It must be something like libmysql.so

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                                micha_eleric
                                wrote on 4 Jan 2024, 21:51 last edited by
                                #23

                                @Christian-Ehrlicher said in error: undefined reference to `mysql_init':

                                It must be something like libmysql.so

                                .so files that show up from mysql search
                                libmysqlclient.so
                                libmysqlclient.so.21
                                libmysqlclient.so.21.2.35
                                mysql_clear_password.so

                                1 Reply Last reply
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                                • M Offline
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                                  micha_eleric
                                  wrote on 4 Jan 2024, 22:47 last edited by
                                  #24

                                  folder /usr/lib/x86_64-linux-gnu/ has libmysqlclient.so

                                  error seems to be with how i have
                                  unix:LIBS += -L/usr/lib/x86_64-linux-gnu -llibmysqlclient

                                  J 1 Reply Last reply 5 Jan 2024, 06:19
                                  0
                                  • M micha_eleric
                                    4 Jan 2024, 22:47

                                    folder /usr/lib/x86_64-linux-gnu/ has libmysqlclient.so

                                    error seems to be with how i have
                                    unix:LIBS += -L/usr/lib/x86_64-linux-gnu -llibmysqlclient

                                    J Offline
                                    J Offline
                                    jsulm
                                    Lifetime Qt Champion
                                    wrote on 5 Jan 2024, 06:19 last edited by
                                    #25

                                    @micha_eleric said in error: undefined reference to `mysql_init':

                                    unix:LIBS += -L/usr/lib/x86_64-linux-gnu -llibmysqlclient

                                    This is wrong. If you use -l you skip the lib prefix:

                                    unix:LIBS += -L/usr/lib/x86_64-linux-gnu -lmysqlclient
                                    

                                    https://forum.qt.io/topic/113070/qt-code-of-conduct

                                    M 1 Reply Last reply 5 Jan 2024, 20:41
                                    1
                                    • M micha_eleric
                                      4 Jan 2024, 21:49

                                      @JonB said in error: undefined reference to `mysql_init':

                                      @micha_eleric
                                      I wonder if you should take a step back and question why you are even trying to do this?

                                      first example found, first example try

                                      You have chosen to pick example code from 2016

                                      does it matter if it is from 2016, or 1908, it showed what library is needed, and how to link libraries, which will be needed for future projects.

                                      J Offline
                                      J Offline
                                      JonB
                                      wrote on 5 Jan 2024, 08:29 last edited by
                                      #26

                                      @micha_eleric said in error: undefined reference to `mysql_init':

                                      does it matter if it is from 2016, or 1908, it showed what library is needed, and how to link libraries, which will be needed for future projects.

                                      Yes, it matters. I tried to advise you that I do not need any -lmysql which you are struggling with. I tried to advise that there is no need and no point using your level of library when writing code for Qt. Tried to advise you that the example you have picked and the code it uses is not the best way at all to go about thing in a Qt program, and you will end up having to do a lot of unnecessary work especially later on if you follow it for a Qt program. You wouldn't need it for future projects, and I have never seen a Qt program which attempts to use mysql_... functions.

                                      All in the spirit of friendly advice, which you are free to take or ignore,

                                      M 1 Reply Last reply 5 Jan 2024, 20:45
                                      3
                                      • J jsulm
                                        5 Jan 2024, 06:19

                                        @micha_eleric said in error: undefined reference to `mysql_init':

                                        unix:LIBS += -L/usr/lib/x86_64-linux-gnu -llibmysqlclient

                                        This is wrong. If you use -l you skip the lib prefix:

                                        unix:LIBS += -L/usr/lib/x86_64-linux-gnu -lmysqlclient
                                        
                                        M Offline
                                        M Offline
                                        micha_eleric
                                        wrote on 5 Jan 2024, 20:41 last edited by
                                        #27

                                        @jsulm thank you for the answer.
                                        two questions:

                                        1. why is part of file name dropped?
                                        2. why can std library be used without these extra steps?
                                        1 Reply Last reply
                                        0
                                        • M micha_eleric has marked this topic as solved on 5 Jan 2024, 20:41
                                        • J JonB
                                          5 Jan 2024, 08:29

                                          @micha_eleric said in error: undefined reference to `mysql_init':

                                          does it matter if it is from 2016, or 1908, it showed what library is needed, and how to link libraries, which will be needed for future projects.

                                          Yes, it matters. I tried to advise you that I do not need any -lmysql which you are struggling with. I tried to advise that there is no need and no point using your level of library when writing code for Qt. Tried to advise you that the example you have picked and the code it uses is not the best way at all to go about thing in a Qt program, and you will end up having to do a lot of unnecessary work especially later on if you follow it for a Qt program. You wouldn't need it for future projects, and I have never seen a Qt program which attempts to use mysql_... functions.

                                          All in the spirit of friendly advice, which you are free to take or ignore,

                                          M Offline
                                          M Offline
                                          micha_eleric
                                          wrote on 5 Jan 2024, 20:45 last edited by
                                          #28

                                          @JonB said in error: undefined reference to `mysql_init':

                                          @micha_eleric said in error: undefined reference to `mysql_init':

                                          does it matter if it is from 2016, or 1908, it showed what library is needed, and how to link libraries, which will be needed for future projects.

                                          Yes, it matters. I tried to advise you that I do not need any -lmysql which you are struggling with. I tried to advise that there is no need and no point using your level of library when writing code for Qt. Tried to advise you that the example you have picked and the code it uses is not the best way at all to go about thing in a Qt program, and you will end up having to do a lot of unnecessary work especially later on if you follow it for a Qt program. You wouldn't need it for future projects, and I have never seen a Qt program which attempts to use mysql_... functions.

                                          All in the spirit of friendly advice, which you are free to take or ignore,

                                          arguing high level vs. low level just encourages me to learn assembly, although i would more likely use C.

                                          C 1 Reply Last reply 5 Jan 2024, 21:01
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