巧用std::shared_ptr
单例的使用相对比较广泛，但是需要在程序退出前调用它的析构函数对数据进行释放，常规做法是在main函数末尾进行释放工作，
但是这样相对比较繁琐，因此便有了利用全局变量由系统负载析构的特点，定义一个全局str::shared_ptr对象，对象指定对单例进行析构。
因此不需要我们关心何时析构单例，堪称方便。
SingleObject.hpp
#ifndef SINGLEOBJECT_H
#define SINGLEOBJECT_H class SingleObject
{
public:
static SingleObject& GetInstance();
static SingleObject* GetInstancePtr();
static void DoSomeThing();
static void DelObj();
private:
static void NewObj();
SingleObject();
~SingleObject(); static SingleObject* msObj;
}; #endif // SINGLEOBJECT_H
SingleObject.cpp
#include "SingleObject.hpp"
#include <iostream>
#include <memory> std::shared_ptr<SingleObject> SingleObjectDeletor( SingleObject::GetInstancePtr(), [](SingleObject *){ SingleObject::GetInstance().DelObj(); }); SingleObject* SingleObject::msObj = NULL; SingleObject::SingleObject()
{
std::cout << "This is the constructor of SignleObject class!\n";
} SingleObject::~SingleObject()
{
std::cout << "This is the destructor of SingleObject class!\n";
} void SingleObject::NewObj()
{
if( NULL == msObj )
{
// lock
msObj = new SingleObject(); // unlock
} std::cout << "New an object, address: " << +msObj << std::endl;
} void SingleObject::DelObj()
{
if( NULL != msObj )
{
delete msObj;
std::cout << "Delete an object!\n";
}
} SingleObject* SingleObject::GetInstancePtr()
{
if( NULL == msObj )
{
NewObj();
} return msObj;
} SingleObject& SingleObject::GetInstance()
{
if( NULL == msObj )
{
NewObj();
} return *msObj;
} void SingleObject::DoSomeThing()
{
std::cout << "SingleObject do some thing!\n";
}
main.cpp
#include <iostream>
#include "SingleObject.hpp" int main(int argc, char **argv)
{
SingleObject::GetInstance().DoSomeThing(); return 0;
}
输出：