Accessing to a static variable from the same class

[xgoan]

So the code that works is this:

objectdatabase.h

...
class ObjectDatabase{
	public:
		static bool openDatabase(QString);
		static bool createTables();
		static void closeDatabase();
		static bool vacuumDatabase();
		static QString errorString();
	protected:
		static void setErrorString(QString);
	private:
		static QString m_errorString;
};
...

...
class ObjectDatabase{
	public:
		static bool openDatabase(QString);
		static bool createTables();
		static void closeDatabase();
		static bool vacuumDatabase();
		static QString errorString();
	protected:
		static void setErrorString(QString);
	private:
		static QString m_errorString;
};
...

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objectdatabase.cpp

...
QString ObjectDatabase::m_errorString;
...
void ObjectDatabase::setErrorString(QString string){
	m_errorString=string;
}
...

...
QString ObjectDatabase::m_errorString;
...
void ObjectDatabase::setErrorString(QString string){
	m_errorString=string;
}
...

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Thanks to all