Accessing to a static variable from the same class

[xgoan]

Hi,

I'm implementing a class to do operations with a SQLite database and I have this header file

...
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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But when I try to access from this functions to the var m_errorString the compiler say that the var isn't defined.

What can be the problem?

Thank's