Unresolved externals

[MarkoSan]

Hello again!

Once I want to compile I get following errors:

File cdatabaseconnection.h:

#ifndef CDATABASECONNECTION_H
#define CDATABASECONNECTION_H
 
// qt headers
#include <QObject>
#include <QSqlDatabase>
 
// c++ stl headers
#include <memory>
 
class CDatabaseConnection : public QSqlDatabase
{
        //Q_OBJECT
 
public:
        //CDatabaseConnection(QObject *parent);
        static std::auto_ptr<CDatabaseConnection>& Instance(QObject *parent);
        ~CDatabaseConnection();
 
private:
        static std::auto_ptr<CDatabaseConnection> m_pInstance;
};
 
//typedef std::auto_ptr<CDatabaseConnection> pdbType;
 
#endif // CDATABASECONNECTION_H

#ifndef CDATABASECONNECTION_H
#define CDATABASECONNECTION_H

// qt headers
#include <QObject>
#include <QSqlDatabase>

// c++ stl headers
#include <memory>

class CDatabaseConnection : public QSqlDatabase
{
        //Q_OBJECT

public:
        //CDatabaseConnection(QObject *parent);
        static std::auto_ptr<CDatabaseConnection>& Instance(QObject *parent);
        ~CDatabaseConnection();
 
private:
        static std::auto_ptr<CDatabaseConnection> m_pInstance;
};

//typedef std::auto_ptr<CDatabaseConnection> pdbType;

#endif // CDATABASECONNECTION_H

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File cdatabaseconnection.cpp:

#include "cdatabaseconnection.h"
 
/*
CDatabaseConnection::CDatabaseConnection(QObject *parent)
        : QSqlDatabase()
{
}
*/
 
CDatabaseConnection::~CDatabaseConnection()
{
}
 
std::auto_ptr<CDatabaseConnection>& CDatabaseConnection::Instance(QObject *parent)
{
        return m_pInstance;
}

#include "cdatabaseconnection.h"

/*
CDatabaseConnection::CDatabaseConnection(QObject *parent)
        : QSqlDatabase()
{
}
*/

CDatabaseConnection::~CDatabaseConnection()
{
}

std::auto_ptr<CDatabaseConnection>& CDatabaseConnection::Instance(QObject *parent)
{
        return m_pInstance;
}

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After compilation, I get linker errors:

Error 1 error LNK2001: unresolved external symbol "private: static class std::auto_ptr<class CDatabaseConnection> CDatabaseConnection::m_pInstance" (?m_pInstance@CDatabaseConnection@@0V?$auto_ptr@VC DatabaseConnection@@@std@@A) cdatabaseconnection.obj
Error 2 fatal error LNK1120: 1 unresolved externals C:\Documents and Settings\markofr.NESRAMNIK\Desktop\QBlagajna\Debug \QKlient.exe

Can someone help me please?

[jpn]

Add

std::auto_ptr<CDatabaseConnection> CDatabaseConnection::m_pInstance = 0;

std::auto_ptr<CDatabaseConnection> CDatabaseConnection::m_pInstance = 0;

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in cdatabaseconnection.cpp.

[MarkoSan]

Add

std::auto_ptr<CDatabaseConnection> CDatabaseConnection::m_pInstance = 0;

std::auto_ptr<CDatabaseConnection> CDatabaseConnection::m_pInstance = 0;

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in cdatabaseconnection.cpp.

Where should I put it, can I put it in main.cpp so I can initialize database at app beginning?

[jpn]

Where should I put it, can I put it in main.cpp so I can initialize database at app beginning?

An initialization of a static member is needed outside the class, in the global scope. I would strongly advise to put the definition (initialization) into cdatabaseconnection.cpp. That's where it belongs, doesn't it? You can access the pointer and initialize the actual connection anywhere you want by just including the header.