QSqlDatabase: QMYSQL driver not loaded / Build MySQL Plugin

[Peter Van Grieken]

(answering myself :-) )

i open the mysql.pro in qtcreator (Coming from windows... I like an ide a lot more than the command line... sorry :-) ) and I added folowing line to this file:

LIBS += -L/home/petervg/Qt5.5.1/5.5/gcc_64/lib

I did this because I knew libQt5Sql.so.5 was located in /home/petervg/Qt5.5.1/5.5/gcc_64/lib.

What I do need to look into, is WHY this works? In /etc/environment I added:

• "PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/home/petervg/Qt5.5.1/Tools/QtCreator/bin/:/home/petervg/Qt5.5.1/5.5/gcc_64/lib:/home/petervg/Qt5.5.1/Tools/QtCreator/lib/qtcreator:/usr/lib"/x86_64-linux-gnu"

and in /home/petervg/.profile I added:

• LIBRARY_PATH="/home/petervg/Qt5.5.1/5.5/gcc_64/lib:/home/petervg/Qt5.5.1/5.5/gcc_64/plugins:/usr/lib/x86_64-linux-gnu:$LIBRARY_PATH"
  LD_LIBRARY_PATH="/home/petervg/Qt5.5.1/5.5/gcc_64/lib:/home/petervg/Qt5.5.1/5.5/gcc_64/plugins:/usr/lib/x86_64-linux-gnu:$LD_LIBRARY_PATH"
  export LIBRARY_PATH
  export LD_LIBRARY_PATH

Neither of these solutions worked.

But my problem us finally solved, so up to the next one... If anybody could shed some light as to why adding the line in the .PRO file worked, but not when adding the path to the environment variables... I'll be glad to know...

Tnx!

[SGaist]

Hi,

The most simple way to ensure you're using the right qmake is to call it with the full path to the executable. One other problem comes from the fact that you also have Qt Creator's stuff in your PATH. Don't do it, Qt Creator comes with it's own build of Qt so that it's a complete autonomous application.

The LIBS += -L/path/ tells the linker where to look for libraries.

[Peter Van Grieken]

Thanks!

I'll take a good look at the PATH variable.

[SGaist]

Leave it clean, that way you ensure that you're not mixing things on your system while building the driver.

[RalfSchaefer]

Hi,

i'm facing a similiar sort of problem, not completely solvable by the steps above.
I recompiled the QMYSQL-plugin and it's linked to the correct mysql-libraries.
After doing ldd /opt/Qt/5.5/gcc_64/plugins/sqldrivers/libqsqlmysql.so I got this:

ldd /opt/Qt/5.5/gcc_64/plugins/sqldrivers/libqsqlmysql.so 
       linux-vdso.so.1 (0x00007fffd7d83000)
       libmysqlclient.so.18 => /usr/lib64/libmysqlclient.so.18 (0x00007f9eb8607000)
        libz.so.1 => /lib64/libz.so.1 (0x00007f9eb83f0000)
        libcrypt.so.1 => /lib64/libcrypt.so.1 (0x00007f9eb81b5000)
        libnsl.so.1 => /lib64/libnsl.so.1 (0x00007f9eb7f9d000)
        libssl.so.1.0.0 => /lib64/libssl.so.1.0.0 (0x00007f9eb7d34000)
        libcrypto.so.1.0.0 => /lib64/libcrypto.so.1.0.0 (0x00007f9eb7941000)
        libQt5Sql.so.5 => /opt/Qt/5.5/gcc_64/lib/libQt5Sql.so.5 (0x00007f9eb7701000)
        libQt5Core.so.5 => /opt/Qt/5.5/gcc_64/lib/libQt5Core.so.5 (0x00007f9eb6fba000)
        libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f9eb6d9d000)
        libstdc++.so.6 => /usr/lib64/libstdc++.so.6 (0x00007f9eb6a1b000)
        libm.so.6 => /lib64/libm.so.6 (0x00007f9eb6719000)
        libgcc_s.so.1 => /lib64/libgcc_s.so.1 (0x00007f9eb6502000)
        libc.so.6 => /lib64/libc.so.6 (0x00007f9eb615b000)
        libdl.so.2 => /lib64/libdl.so.2 (0x00007f9eb5f56000)
        libicui18n.so.54 => /opt/Qt/5.5/gcc_64/lib/libicui18n.so.54 (0x00007f9eb5ae8000)
        libicuuc.so.54 => /opt/Qt/5.5/gcc_64/lib/libicuuc.so.54 (0x00007f9eb5739000)
        libicudata.so.54 => /opt/Qt/5.5/gcc_64/lib/libicudata.so.54 (0x00007f9eb3d0f000)
        libgthread-2.0.so.0 => /usr/lib64/libgthread-2.0.so.0 (0x00007f9eb3b0d000)
        librt.so.1 => /lib64/librt.so.1 (0x00007f9eb3904000)
        libglib-2.0.so.0 => /usr/lib64/libglib-2.0.so.0 (0x00007f9eb35f5000)
        /lib64/ld-linux-x86-64.so.2 (0x000055fc1f3d8000)
        libpcre.so.1 => /usr/lib64/libpcre.so.1 (0x00007f9eb338e000)

So, erverything looks fine here.

When I try to connect to the database, it still doesn't work. It seems, QSqlDatabase loads the plugin without problems, setting dabase specific stuff fails.

My code-snippet, containing additional debug-stuff:

    QPluginLoader loader;
    loader.setFileName("/opt/Qt/5.5/gcc_64/plugins/sqldrivers/libqsqlmysql.so");
    qDebug() << "PluginLoader worked =" << loader.load();
    qDebug() << "Plugin Loader error=" << loader.errorString();

    QStringList driverlist =QSqlDatabase::drivers();
    qDebug() << "Databases: ";
    for (int i = 0; i < driverlist.size(); ++i)
    {
        qDebug() << driverlist.at(i);
    }

    if (!db_opened)
    {
            db = new QSqlDatabase();
            qDebug() << "Step 1 - Database:    is valid=" << db->isValid();
            db->addDatabase("QMYSQL3","cooptimedb");
            qDebug() << "Step 2 - Database:    is valid=" << db->isValid();

            db->setHostName("localhost");
            db->setDatabaseName("cooptime");
            db->setUserName("cooptime");
            db->setPassword("...");
            db->setPort(3306);

            qDebug() << "Database\n========\nHostname: " << db->hostName() << "\nDatabasename: " << db->databaseName() << "\nUsername: " << db->userName() << "\nPassword: " << db->password()  << "\nPort: " << db->port();


            if (! db->open())
            {
                qDebug() << "db errorcode=" <<  db->lastError().nativeErrorCode();
                qDebug() << "db errormessage=" << db->lastError() .text();
            }

The output of the code above is:

PluginLoader worked = true
Plugin Loader error= "Unknown error"
Databases: 
"QSQLITE"
"QMYSQL"
"QMYSQL3"
"QPSQL"
"QPSQL7"
Step 1 - Database:    is valid= false
Step 2 - Database:    is valid= false
Database
========
Hostname:  "" 
Databasename:  "" 
Username:  "" 
Password:  "" 
Port:  -1
db errorcode= ""
db errormessage= "Driver not loaded Driver not loaded"

So it seems, the driver still doesn't load.

Any help would be very appreciated. Thanks in advance.

[SGaist]

Hi and welcome to devnet,

Your code is wrong, you are creating an invalid QSqlDatabase object on the heap and then you call a static function on it.

Please take a look at QSqlDatabase's detailed documentation. There's an example there on how to do the setup and connection.

[RalfSchaefer]

@SGaist Thanks for your help!! That's it. Now all works fine for me!

[fikou1335]

Hi SGaist,

I have a new problem with QMysql, everything worked fine since today, actually when I executede this line

    DB = QSqlDatabase::addDatabase( "QMYSQL");

I have this error

libgcc_s.so.1 must be installed for pthread_cancel to work

I don't know why,

the plugin is correctly compiled without error, and using the ldd he found the libgcc_s.so.1

Can you help me please!

[SGaist]

Hi and welcome to devnet,

Which architecture are on ?

[fikou1335]

Hi and thanks for your quick response

I m working on Ubuntu 64bits
i got this

Precision-M4600:/usr/local/Trolltech/Qt-4.8.6/plugins/sqldrivers$ ldd libqsqlmysql.so 	linux-vdso.so.1 =>  (0x00007ffceb314000)
	libmysqlclient.so.18 => /usr/lib/x86_64-linux-gnu/libmysqlclient.so.18 (0x00007f7a884c6000)
	libQtSql.so.4 => /usr/local/Trolltech/Qt-4.8.6/lib/libQtSql.so.4 (0x00007f7a88285000)
	libQtCore.so.4 => /usr/local/Trolltech/Qt-4.8.6/lib/libQtCore.so.4 (0x00007f7a87d91000)
	libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f7a87a7f000)
	libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f7a87868000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f7a874a3000)
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f7a8728a000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f7a87086000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f7a86e68000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f7a86b62000)
	librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f7a8695a000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f7a88c10000)

and this

Precision-M4600:/usr/lib/x86_64-linux-gnu$ ldd libmysqlclient.so.18
	linux-vdso.so.1 =>  (0x00007ffe50bc0000)
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007fe8f4940000)
	libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007fe8f473c000)
	libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007fe8f451e000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007fe8f4218000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fe8f3e53000)
	/lib64/ld-linux-x86-64.so.2 (0x00007fe8f5091000)

If I comment the addBase line in my code everything works fine without connecting to the Database of course.
when I try to list the drivers using

QStringList driverlist =QSqlDatabase::drivers();

I got this

Databases: QSQLITE QMYSQL3 QMYSQL

Everything works fine Monday, I checked the database, I could write on it fine,, but yesterday, it crash my application
hope it can help!

[fikou1335]

I have just created a new app with the main function and it works and connect fine to my database.

In my code I comment all the last code that I added this week and SURPRISE it works as well.
the problem is probably due to a third library that i started to use this week. I ll check why it cause a crach to mysql o_O

[SGaist]

What new library did you add ?

[fikou1335]

This one Dahua SDK

You can check by yourslef, they have a source example, PTZControl that works fine, but try to add

      DB = QSqlDatabase::addDatabase( "QMYSQL");   

and you should get the same error.

this sdk is used to control PTZ cams of Dahua brand.
I changed my code by creating a new app to control cameras and get the informations of position from my big application.

put this main instsead of it

#include <QtGui/QApplication>
#include "dialog.h"
#include <QTextCodec>
#include <QObject>
#include <QtSql/QSqlDatabase>
#include <QStringList>
#include <QtSql/QSqlQuery>
#include <QtSql/QSqlRecord>
#include <QVariant>
#include <iostream>



int main(int argc, char *argv[])
{
    QSqlDatabase DB;
    cout <<endl<< "try connect MYSQL "<< endl;
    try
    {
        DB = QSqlDatabase::addDatabase( "QMYSQL");
    }
    catch(...)
    {
        cout << "fatal error"<< endl;
    }
    cout << "add database"<< endl;
    DB.setDatabaseName( "intrusiondetection" );
    DB.setUserName( "root" );

    DB.setPassword( "root" );
    cout << "1"<< endl;

    DB.setHostName( "" );

    cout << "try to connect"<< endl;
    if (DB.open())
    {
        cout << "QMYSQL correctly connected "<< endl;
    }
    else
    {
        cout << "QMYSQL not connected "<< endl;
    }


    QApplication a(argc, argv);
    QTextCodec::setCodecForCStrings(QTextCodec::codecForName("UTF-8"));
    Dialog w;
    w.show();

    return a.exec();
}

tell me if you got the same error.?

[SGaist]

One thing that you should first correct: move the database initialization code after the QApplication object creation.

[fikou1335]

i already tried every configuration but doesn't work! just a question by the way:
Is the QDbus available on the Ubuntu system since they said it is Unix only library..? I try to communicate between PTZcontrol process and my application

[SGaist]

Ubuntu is a unix based OS since it's based on the Debian distribution. QDBus is available on Linux, OS X and Windows (the two later requires that you install dbus by hand)

[Hervinsen]

Thanks to your guide, it is working on Kubuntu 16 with Qt 5.8
here is my output :

• /opt/Qt5.8.0/5.8/gcc_64/plugins/sqldrivers$ ldd libqsqlmysql.so
  linux-vdso.so.1 => (0x00007ffcf0bf4000)
  libQt5Sql.so.5 => /opt/Qt5.8.0/5.8/gcc_64/plugins/sqldrivers/./../../lib/libQt5Sql.so.5 (0x00007f28a7452000)
  libQt5Core.so.5 => /opt/Qt5.8.0/5.8/gcc_64/plugins/sqldrivers/./../../lib/libQt5Core.so.5 (0x00007f28a6d32000)
  libmysqlclient.so.20 => /usr/lib/x86_64-linux-gnu/libmysqlclient.so.20 (0x00007f28a66fa000)
  libstdc++.so.6 => /usr/lib/x86_64-linux-gnu/libstdc++.so.6 (0x00007f28a6372000)
  libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f28a5fa2000)
  libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f28a5d82000)
  libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f28a5a72000)
  libgcc_s.so.1 => /lib/x86_64-linux-gnu/libgcc_s.so.1 (0x00007f28a585a000)
  libicui18n.so.56 => /opt/Qt5.8.0/5.8/gcc_64/plugins/sqldrivers/./../../lib/libicui18n.so.56 (0x00007f28a53ba000)
  libicuuc.so.56 => /opt/Qt5.8.0/5.8/gcc_64/plugins/sqldrivers/./../../lib/libicuuc.so.56 (0x00007f28a5002000)
  libicudata.so.56 => /opt/Qt5.8.0/5.8/gcc_64/plugins/sqldrivers/./../../lib/libicudata.so.56 (0x00007f28a361a000)
  libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f28a3412000)
  librt.so.1 => /lib/x86_64-linux-gnu/librt.so.1 (0x00007f28a320a000)
  libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f28a2fea000)
  libgthread-2.0.so.0 => /usr/lib/x86_64-linux-gnu/libgthread-2.0.so.0 (0x00007f28a2de2000)
  libglib-2.0.so.0 => /lib/x86_64-linux-gnu/libglib-2.0.so.0 (0x00007f28a2aca000)
  /lib64/ld-linux-x86-64.so.2 (0x0000560448d0b000)
  libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f28a285a000)

[Amit Talbot]

im using qt 5.9 on mac this piece of code worked like charm for me

brew install mysql-connector-c