object inicialization with constructor in QT, no matching function to call - c++

Question

I'm using Mysql 5.6 with Qt5 and creating a class to encapsulate a database connection.
When I try to create an object in the main with dbConnect conn = new dbConnect("localhost", "test1","test","user"); I get and error telling me I need a conversion from dbConnect* to a non-scalar type.
Reading other posts I've seen this could be due to the type of inicialization I'm trying because it's not a good practice in C++ and should be something like dbConnect conn("localhost", "test1","test","user"); but, changing it like that, instead of getting the conversion error I get now a no matching function for call to QSqlDatabase::setHosTname(std::string&) and same with the other methods needed for connecting such as setDatabaseName, setUserName and setPassword
Could it be because of the std::string I'm using?
Or how should I create the object?
This is m y header db.h:
#ifndef DB
#define DB
#include <QSqlDatabase>
#include <string>
class dbConnect:QSqlDatabase
{
public:
dbConnect(std::string host, std::string name,std::string user, std::string pass);
bool createConnection(std::string host, std::string name,std::string user, std::string pass);
private:
QSqlDatabase dbObject;
};
#endif // DB_
Next here it is its implementation db.cpp:
#include<QSqlDatabase>
#include <QMessageBox>
#include <QSqlError>
class dbConnect:QSqlDatabase
{
private:
QSqlDatabase dbObject;
public:
dbConnect(std::string host, std::string name,std::string user, std::string pass)
{
if(createConnection(host, name, user, pass))
{
QMessageBox::information(0,"Connection Status","Connection established with database");
}
else
{
QMessageBox::critical(0,QObject::tr("Error connecting to database"),dbObject.lastError().text());
}
}
bool createConnection(std::string host, std::string name,std::string user, std::string pass)
{
dbObject = QSqlDatabase::addDatabase("QMYSQL");
dbObject.setHostName(host);
dbObject.setDatabaseName(name);
dbObject.setUserName(user);
dbObject.setPassword(pass);
if(!dbObject.open())
{
return false;
}
else
{
return true;
}
}
};
UPDATE
Took #gengisdave and #R Sahu solutions and now I'm trying to create an object in the main. If I try dbConnect conn(); it works fine even if the constructor takes for paremeter but, if I trye dbConnect conn("localhost","test1","test","user"); compiler gives me an error of undefined reference to dbConnect::dbConnect(std::string,std::string,std::string,std::string).

Answer 1

When you use:
dbConnect conn = new dbConnect("localhost", "test1","test","user");
the RHS is of type dbConnect* while the LHS is of type dbConnect. That is not correct. The compiler cannot take a pointer and assign it to an object.
You can use:
dbConnect* connPtr = new dbConnect("localhost", "test1","test","user");
or
dbConnect conn("localhost", "test1","test","user");
Other problems
bool createConnection(std::string host, std::string name,std::string user, std::string pass)
{
dbObject = QSqlDatabase::addDatabase("QMYSQL");
dbObject.setHostName(host);
dbObject.setDatabaseName(name);
dbObject.setUserName(user);
dbObject.setPassword(pass);
if(!dbObject.open())
{
return false;
}
else
{
return true;
}
}
is not right. You probably need:
bool createConnection(std::string host, std::string name,std::string user, std::string pass)
{
// Since this class is derived from QSqlDatabase,
// you can use:
this->addDatabase("QMYSQL");
this->setHostName(QString::fromStdString(host));
this->setDatabaseName(QString::fromStdString(name));
this->setUserName(QString::fromStdString(user));
this->setPassword(QString::fromStdString(pass));
if(!this->open())
{
return false;
}
else
{
return true;
}
}
Also, remove the member variable
QSqlDatabase dbObject;
You don't need it since the class is already derived from QSqlDatabase. You'll need to use that only if you don't derive from QSqlDatabase

Answer 2

QSQlDatabase::setHostName requires a parameter of type QString, while you provide a std::string; the same with the next 3 lines
you can change that lines to
this->setHostName(QString::fromStdString(host));
this->setDatabaseName(QString::fromStdString(name));
this->setUserName(QString::fromStdString(user));
this->setPassword(QString::fromStdString(pass));
EDIT: it works fine
main.cpp
#include <QApplication>
#include "db.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
dbConnect connection("localhost", "test1", "test", "user");
dbConnect *conn = new dbConnect("localhost", "test1", "test", "user");
}
db.cpp
#include <QSqlDatabase>
#include <QMessageBox>
#include <QSqlError>
#include "db.h"
dbConnect::dbConnect(std::string host, std::string name,std::string user, std::string pass)
{
if ( createConnection(host, name, user, pass) )
QMessageBox::information(0, "Connection Status", "Connection established with database");
else
QMessageBox::critical(0,QObject::tr("Error connecting to database"),dbObject.lastError().text());
}
bool dbConnect::createConnection(std::string host, std::string name,std::string user, std::string pass)
{
this->dbObject = QSqlDatabase::addDatabase("QMYSQL");
this->dbObject.setHostName(QString("localhost"));
this->dbObject.setDatabaseName(QString("test.txt"));
this->dbObject.setUserName(QString("test"));
this->dbObject.setPassword(QString("test"));
return this->dbObject.open();
}
db.h
#ifndef DB_H
#define DB_H
#include <QSqlDatabase>
#include <string>
class dbConnect:QSqlDatabase
{
public:
dbConnect(std::string host, std::string name,std::string user, std::string pass);
bool createConnection(std::string host, std::string name,std::string user, std::string pass);
private:
QSqlDatabase dbObject;
};
#endif
compiled with: gcc db.cpp main.cpp -I/usr/include/qt5/QtSql -I/usr/include/qt5/QtWidgets -I/usr/include/qt5 -fPIC -o main -lstdc++ -lQt5Sql -lQt5Core -lQt5Widgets