Qt单例：Qt有专门的宏Q_GLOBAL_STATIC，用来实现线程安全的单例模式

#ifndef RULE_H
#define RULE_H
#include <QGlobalStatic>
#define RULE Rule::instance()
class Rule
{
public:
    Rule() {}
    virtual ~Rule() {}
public:
    static Rule* instance();
public:
    void test();
};
#endif // RULE_H

#include "rule.h"
Q_GLOBAL_STATIC(Rule, rule)
Rule* Rule::instance()
{
    return rule();
}
void Rule::test()
{
    //todo
}