单例模式的学习

示例：

#ifndef TEST_H
#define TEST_Hclass test
{
public:static test * GetINSTANCE();void print();
private:test();
};#endif // TEST_H

#include "test.h"
#include <QMutex>
#include <QDebug>
test::test()
{}test *test::GetINSTANCE()
{static test * inst = nullptr;static QMutex mutex;mutex.lock();if(!inst){inst = new test;}mutex.unlock();return inst;
}void test::print()
{static int m = 0;m++;qDebug()<<__FILE__<<"["<<__LINE__<<"]"<< m;
}

补充：

这样写也可以：

    static T * GetINSTANCE(){static QScopedPointer<T> inst;static QMutex mutex;mutex.lock();if(!inst){inst.reset(new T());}mutex.unlock();return inst.data();}

    test::GetINSTANCE()->print();test::GetINSTANCE()->print();test::GetINSTANCE()->print();

..\try\test.cpp [ 26 ] 1

..\try\test.cpp [ 26 ] 2

..\try\test.cpp [ 26 ] 3

使用类模板进行简单的优化，使代码扩展性更好一些：

#ifndef TEST_H
#define TEST_H#include <QMutex>template<typename T>
class Singleton
{
public:static T * GetINSTANCE(){static T * inst = nullptr;static QMutex mutex;mutex.lock();if(!inst){inst = new T();}mutex.unlock();return inst;}
protected:Singleton() = default;
};class test:public Singleton<test>
{friend class Singleton<test>;
public:void print();
private:test() = default;
};
#endif // TEST_H

#include "test.h"
#include <QDebug>void test::print()
{static int m = 0;m++;qDebug()<<__FILE__<<"["<<__LINE__<<"]"<< m;
}

    test::GetINSTANCE()->print();test::GetINSTANCE()->print();test::GetINSTANCE()->print();

..\try\test.cpp [ 11 ] 1

..\try\test.cpp [ 11 ] 2

..\try\test.cpp [ 11 ] 3