How to write a QList into a binary file?

How can I write a QList into a binary file since the QDataStream.operator<<() and QDataStream.operator>>() have no corresponding overload in which I can pass in a QList.

In the application I am writing, there is a Patient class which I have a QList of and I want to read it from a binary file at startup and manipulate it throughout the execution, then at the end, write it back into the same file.

Any advice?

it depends which type you use in template.

Thanks for replying, the QList is of type Patient which is a class I defined, and I am getting an error when trying to write the list to a binary file, here is some code:

Code:

---

class Patient
{
public:
	Patient();
private:
	QString firstName;
	QString lastName;
};
 
int main()
{
	QList<Patient> patientList;
	QFile qFile("Patient_List.bin");
	if (qFile.open(QIODevice::ReadOnly))
	{
		QDataStream in(&qFile);
		in >> patientList;	//error here
	}
}

---

implement your own QDataStrem:: operator << & >> for this type and everything should work.

You mean something like this:

Code:

---

QDataStream& QDataStream::operator>>(Patient patient)
{
	*this >> patient.firstName;
	*this >> patient.lastName;
 
    return *this;
}
 
QDataStream& QDataStream::operator<<(Patient patient)
{
	*this << patient.firstName;
	*this << patient.lastName;
 
    return *this;
}

---

almost, I would use these signatures. :)

Code:

---

QDataStream &operator<<(QDataStream &in, const Patient &patient)
{
...
}
 
QDataStream &operator>>(QDataStream &in, Patient &patient)
{
...
}

---

Please bear with me :),
I defined those in the patient.cpp file:

Code:

---

QDataStream& QDataStream::operator<<(QDataStream &in, const Patient &patient)
{
	in << patient.firstName;
	in << patient.lastName;
 
    return in;
}
 
QDataStream& QDataStream::operator>>(QDataStream &out, Patient &patient)
{
	out >> patient.firstName;
	out >> patient.lastName;
 
    return out;
}

---

but I got these errors at the opening curly brace of operator<<:

Code:

---

Multiple markers at this line
	- non-inline function 'QDataStream& QDataStream::operator<<(QDataStream&, const 
	 Patient&)' is defined after prior declaration as dllimport: attribute ignored
	- prototype for `QDataStream& QDataStream::operator<<(QDataStream&, const Patient&)' 
	 does not match any in class `QDataStream'
	- `QDataStream& QDataStream::operator<<(QDataStream&, const Patient&)' must take 
	 exactly one argument

---

and these errors at the opening curly brace of operator>>:

Code:

---

Multiple markers at this line
	- `QDataStream& QDataStream::operator>>(QDataStream&, Patient&)' must take 
	 exactly one argument
	- prototype for `QDataStream& QDataStream::operator>>(QDataStream&, Patient&)' 
	 does not match any in class `QDataStream'

---

what's wrong? :(

Here:

Code:

---

//spirit's code:
QDataStream &operator<<(QDataStream &in, const Patient &patient)
 
 
//Your code:
QDataStream& QDataStream::operator<<(QDataStream &in, const Patient &patient)
             ^^^^^^^^^^^^^

---

try this example
h - file

Code:

---

class Foo
{
public:
	Foo(int number = 0, const QString &name = QString()) 
		: m_number(number), m_name(name)
	{}
 
	void setNumber(int number) { m_number = number; }
	int number() const { return m_number; }
 
	void setName(const QString &name) { m_name = name; }
	QString name() const { return m_name; }
 
private:
	int m_number;
	QString m_name;
};
 
QDataStream &operator<<(QDataStream &out, const Foo &foo);
QDataStream &operator>>(QDataStream &in, Foo &foo);

---

cpp-file

Code:

---

QFile file("test.txt");
if (!file.open(QIODevice::WriteOnly))
	return;
 
QDataStream out(&file);
QList<Foo> res;
for (int i = 0; i < 11; ++i) {
	Foo f(i, tr("name%1").arg(i));
	res << f;
}
out << res;
file.close();
 
if (!file.open(QIODevice::ReadOnly))
	return;
 
QDataStream in(&file);	
res.clear();
in >> res;
 
for (int i = 0; i < res.size(); ++i) {
	const Foo f = res.at(i);
	qDebug() << f.number() << " " << f.name();
}

---

Thank you JhonJames and spirit, writing and reading the List are working!

I have a similar kind of problem. I want to write a QList with custom classes to a binary file.

I want to write a

Code:

---

static QList<Server> serversList;

---

to a binary file

I my server.cpp i have the following lines of code:

Code:

---

QDataStream& operator<<(QDataStream& out, const Server& server)
{
    out << server.serverAddres;
    ...
    out << server.serverUseSsl;
    return out;
}
 
QDataStream& operator>>(QDataStream& in,Server& server)
{
    in >> server.serverAddres;
    ...
    in >> server.serverUseSsl;
    return in;
}

---

In the file serverlist.cpp i do the operation:

Code:

---

if(!serverDataFile.open(QIODevice::ReadWrite))
    {
        return;
    }
 
    outputStream = new QDataStream(&serverDataFile);
    outputStream << listofServers;

---

but when i compile i get the following error;

Code:

---

O:/projects/Post_Program/serverlist.cpp:44: error: no match for 'operator<<' in '((serverList*)this)->serverList::outputStream << serverList::listofServers'

---

I think outputStream should be a QDataStream instead of QDataStream* for your code to work...

Or (if it has to be a QDataStream*) you gotta find another to call operator<<() such as:

Code:

---

(*outputStream) << listofServers

---

Thanks that solved the problem but created a new one.
I now get the following error:

Code:

---

f:/Qt/2009.02/qt/include/QtCore/../../src/corelib/io/qdatastream.h: In function 'QDataStream& operator<<(QDataStream&, const QList<T>&) [with T = Server]':
serverlist.cpp:45: instantiated from here
f:/Qt/2009.02/qt/include/QtCore/../../src/corelib/io/qdatastream.h:252: error: no match for 'operator<<' in 's << (+l)->QList<T>::at [with T = Server](i)'

---

What are the types of server.serverAddres and server.serverUseSsl? because you might have to overload operator<<() and operator>>() on them...
As the Assistant puts it:

Quote:

---

The QDataStream class implements the serialization of C++'s basic data types, like char, short, int, char *, etc. Serialization of more complex data is accomplished by breaking up the data into primitive units.

---

Server consits of a few QString's some bool's and qint32.

Would you post the full code of the serverlist.cpp file

This is the serverlist.cpp:

Code:

---

#include <QDir>
#include <QMessageBox>
 
#include "serverlist.h"
 
QList<Server> listofServers;
 
 
serverList::serverList()
{
    settings = new Settings();
    QFile serverDataFile(settings->getappDataDir() + QDir::separator() + "servers" + QDir::separator() + "servers.dat");
    serverDataFileInfo = new QFileInfo(serverDataFile);
    QDataStream outputStream(&serverDataFile);
    QDataStream inputStream(&serverDataFile);
}
 
void serverList::saveServers()
{
    if(serverDataFileInfo->exists())
    {
        QDir newFile(serverDataFileInfo->absoluteFilePath());
        newFile.mkpath(serverDataFileInfo->absolutePath());
    }
    if(!serverDataFile.open(QIODevice::ReadWrite))
    {
        QMessageBox::critical( 0, "Post program","There was a problem reading the server settings file" );
    }
    outputStream << listofServers;
}
 
void serverList::addServer(Server newServer)
{
}

---

This is the serverlist.h:

Code:

---

#ifndef SERVERLIST_H
#define SERVERLIST_H
 
#include <QList>
#include <QFile>
#include <QFileInfo>
#include <QDataStream>
 
#include <server.h>
#include <settings.h>
 
class serverList
{
public:
    serverList();
    void saveServers();
    void addServer(Server newServer);
    void loadServers();
 
private:
    static QList<Server> listofServers;
    Settings *settings;
    QFileInfo *serverDataFileInfo;
    QFile serverDataFile;
    QDataStream outputStream;
    QDataStream inputStream;
};
 
#endif // SERVERLIST_H

---

I will post the Server class also to get the complete picture
server.cpp:

Code:

---

#include "server.h"
//#include <QDataStream>
 
Server::Server()
{
}
 
void Server::setAddres(QString newAddres)
{
    serverAddres = newAddres;
}
 
void Server::setNickname(QString newNickname)
{
    serverNickname = newNickname;
}
 
void Server::setPort(qint32 newPort)
{
    serverPort = newPort;
}
 
void Server::setConnections(qint32 newConnections)
{
    serverConnections = newConnections;
}
 
void Server::setUsername(QString newUsername)
{
    serverUsername = newUsername;
}
 
void Server::setPassword(QString newPassword)
{
    serverPassword = newPassword;
}
 
void Server::setRequireLogin(bool newRequireLogin)
{
    serverRequireLogin = newRequireLogin;
}
 
void Server::setUseSsl(bool newUseSsl)
{
    serverUseSsl = newUseSsl;
}
 
QString Server::getAddres()
{
    return serverAddres;
}
 
QString Server::getNickname()
{
    return serverNickname;
}
 
qint32  Server::getPort()
{
    return serverPort;
}
 
qint32  Server::getConnections()
{
    return serverConnections;
}
 
QString Server::getUsername()
{
    return serverUsername;
}
 
QString Server::getPassword()
{
    return serverPassword;
}
 
bool    Server::getRequireLogin()
{
    return serverRequireLogin;
}
 
bool    Server::getUseSsl()
{
    return serverUseSsl;
}
 
 
 
QDataStream& operator<<(QDataStream& out, const Server& server)
{
    out << server.serverAddres;
    out << server.serverNickname;
    out << server.serverPort;
    out << server.serverConnections;
    out << server.serverUsername;
    out << server.serverPassword;
    out << server.serverRequireLogin;
    out << server.serverUseSsl;
    return out;
}
QDataStream& operator>>(QDataStream& in,Server& server)
{
    in >> server.serverAddres;
    in >> server.serverNickname;
    in >> server.serverPort;
    in >> server.serverConnections;
    in >> server.serverUsername;
    in >> server.serverPassword;
    in >> server.serverRequireLogin;
    in >> server.serverUseSsl;
    return in;
}

---

server.h

Code:

---

#ifndef SERVER_H
#define SERVER_H
 
#include <QString>
#include <QtGlobal>
 
 
class Server
{
public:
    Server();
 
    //Set functions
    void setAddres(QString newAddres);
    void setNickname(QString newNickname);
    void setPort(qint32 newPort);
    void setConnections(qint32 newConnections);
    void setUsername(QString newUsername);
    void setPassword(QString newPassword);
    void setRequireLogin(bool newRequireLogin);
    void setUseSsl(bool newUseSsl);
 
    //Get functions
    QString getAddres();
    QString getNickname();
    qint32  getPort();
    qint32  getConnections();
    QString getUsername();
    QString getPassword();
    bool    getRequireLogin();
    bool    getUseSsl();
 
private:
    QString serverAddres;
    QString serverNickname;
    qint32  serverPort;
    qint32  serverConnections;
    QString serverUsername;
    QString serverPassword;
    bool    serverRequireLogin;
    bool    serverUseSsl;
};
#endif // SERVER_H

---

In my case, I declared the functions operator<<() and operator>>() in the .h file and implemented them in the .cpp file, and when I tried removing the declarations from the .h file I got the very same error you got.

So, put those 2 lines in the server.h file:

Code:

---

QDataStream& operator<<(QDataStream& out, const Server& server);
QDataStream& operator>>(QDataStream& in,Server& server);

---

Thanks that worked. Now i have to look at my implementation of the reading of a file because it is complaining about a missing operator at the bool's and qint32's but they should be available according to the documentation.

Code:

---

O:/projects/Post_Program/server.cpp:107: error: no match for 'operator>>' in 'in >> server->Server::serverPort'

---

Wait a minute, aren't those members private? how are you accessing them directly?

To test it i made the public.

That error you're getting doesn't necessarily mean what you think it means, sometimes GCC errors are ambiguous.

I copied all the code as-is into a project in my PC then added the two line I told you about (the declarations) and it turend out that you should un-hint the "#include <QDataStream>" and the error will go away...

I tried it and it works. Thanks everything works now.

It's good to know that :)