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Qt-interest Archive, February 2007
Wrong encoding from MySQL

Message 1 in thread

Hello trolls,

Recently I got a problem of getting data from MySQL (5.0.16) table, that 
in Windows-1251 encoding. I'm using Qt 4.2.2 and VS2005. As I'm trying 
to get the values from DB, i got either ??? or characters of another 
encoding.

Hope on your help!

Below is the code of my program:

QtSQL::QtSQL(QWidget *parent, Qt::WFlags flags)
	: QMainWindow(parent, flags)
{
	ui.setupUi(this);

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

	db.setUserName("root");
	db.setPassword("root");
	db.setHostName("localhost");
	db.setDatabaseName("test");

	bool opened = db.open();
	if (!opened) QMessageBox::information(this, "title", "problem", 
QMessageBox::Ok);

	QSqlQuery q("SET NAMES cp1251;");

}

void QtSQL::on_btn_2_clicked()
{
	QSqlQuery q("SELECT * FROM `encoding` WHERE ID = 10;");
	q.next();

	QSqlRecord rec = q.record();

	// it works fine if I uncomment the following lines, but I believe it 
should not be done this way! :)
	//QByteArray encodedString = rec.value("Text").toByteArray();
	//QTextCodec *codec = QTextCodec::codecForName("Windows-1251");
	//QString string = codec->toUnicode(encodedString);
	
	QString string = rec.value("Text").toString();

QTextCodec::setCodecForCStrings(QTextCodec::codecForName("windows-1251"));	

	ui.txt->setText(string);
}

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Message 2 in thread

Hi,

> Recently I got a problem of getting data from MySQL (5.0.16) table, that 
> in Windows-1251 encoding. I'm using Qt 4.2.2 and VS2005. As I'm trying 
> to get the values from DB, i got either ??? or characters of another 
> encoding.

I'm not really a specialist, but whatever the internal MySQL encoding, 
you shouldn't have to worry about it with recent MySQL versions. From 
the Qt 4.2 MySQL driver source file:
	bool QMYSQLDriver::open(...)
	{
	[...]
	#if MYSQL_VERSION_ID >= 50007
	    // force the communication to be utf8
	    mysql_set_character_set(d->mysql, "utf8");
	#endif

Since you have MySQL 5.0.16, Qt should be able to retrieve strings 
without further decoding, whatever the internal encoding of the database.

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Message 3 in thread

Hello everyone,

I am reading a classic article: A Byte of Python, which says
a Python class has two types of fields - class variables and object 
variables.

class Person:
    population = 0 # class variable
    def __init__(self, name):
        self.name = name # object variable
        Person.population += 1

“Class variables are shared in the sense that they are accessed by all 
objects (instances) of that class. There is only copy of the class 
variable and when any one object makes a change to a class variable, the 
change is reflected in all the other instances as well.”

“Object variables are owned by each individual object/instance of the 
class. In this case, each object has its own copy of the field i.e. they 
are not shared and are not related in any way to the field by the same 
name in a different instance of the same class. An example will make 
this easy to understand.”
(see 
http://swaroopch.info/text/Byte_of_Python:Object_oriented_programming )

I know all Qt developers are C++ experts, and they are object-orientated.
I wonder how to implement the class and object variables in C++.
Can anyone help to translate the above 5-line Python class into a C++ 
class?

Thanks in advance,
Lingfa


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Message 4 in thread

On 06.02.07 17:57:27, lingfa wrote:
> I am reading a classic article: A Byte of Python, which says
> a Python class has two types of fields - class variables and object variables.
> 
> I know all Qt developers are C++ experts,

Certainly not, there are bindings for Qt for Python and Ruby. Maybe have
a look into those, then you don't need to learn C++.

> and they are object-orientated.
> I wonder how to implement the class and object variables in C++.
> Can anyone help to translate the above 5-line Python class into a C++ class?

C++ has the same thing, the difference is that its defined at compile
time, all class variables have the static keyword in front and all other
variables are automatically object variables.

Andreas

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Message 5 in thread

Hi,

as Andreas said there are some Python binding for C++, e.g.:

Elmer (free): http://elmer.sourceforge.net/
PythonQt (free):  http://pythonqt.sourceforge.net/index.html
PyQt (commercial):  http://www.riverbankcomputing.co.uk/pyqt/

Your class would be in C++:

class Person {
public:
  // __init__ / constructor
  Person(string name) : m_Name(name) { population++; }

protected:
  static int population;   // class variable
};

// statics must be initialized outside the class
static int Person.population = 0;   

Just a simple example - there are many good C++ tutorials in the net.

Best Regards,
Christian



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Message 6 in thread

Thanks, Christian for your references and code, and
thanks, Andreas for your comments.
The binding seems more interesting.
Lingfa


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Message 7 in thread

Hi Christian,

allow me to nitpick for clarity's sake; Python code doesn't really mix 
with C++ sources ;-)

Christian Dähn schrieb:
> Your class would be in C++:
> 
> class Person {
> public:
>   // __init__ / constructor
>   Person(string name) : m_Name(name) { population++; }
> 
> protected:
>   static int population;   // class variable

string m_Name;	//Declaration missing

> };
> 
> // statics must be initialized outside the class
> static int Person.population = 0;   

int Person::population = 0;	//Static scope resolution


Martin
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