用代碼詳解C++11中std::shared_ptr總結(jié)與使用

std::shared_ptr<Test> p1(new Test);
std::shared_ptr<Test> p2(new Test);
p1 = p2;

std::shared_ptr<Test> p = std::make_shared<Test>();
std::shared_ptr<Test> p(new Test);

include <iostream>
#include <memory>
#include <thread>
#include <chrono>
#include <mutex>

struct Test
{
 Test() { std::cout << " Test::Test()\n"; }
 ~Test() { std::cout << " Test::~Test()\n"; }
};

//線程函數(shù)
void thr(std::shared_ptr<Test> p)
{
 //線程暫停1s
 std::this_thread::sleep_for(std::chrono::seconds(1));

 //賦值操作, shared_ptr引用計數(shù)use_cont加1(c++11中是原子操作)
 std::shared_ptr<Test> lp = p;
 {
 //static變量(單例模式),多線程同步用
 static std::mutex io_mutex;

 //std::lock_guard加鎖
 std::lock_guard<std::mutex> lk(io_mutex);
 std::cout << "local pointer in a thread:\n"
 << " lp.get() = " << lp.get()
 << ", lp.use_count() = " << lp.use_count() << '\n';
 }
}

int main()
{
 //使用make_shared一次分配好需要內(nèi)存
 std::shared_ptr<Test> p = std::make_shared<Test>();
 //std::shared_ptr<Test> p(new Test);

 std::cout << "Created a shared Test\n"
 << " p.get() = " << p.get()
 << ", p.use_count() = " << p.use_count() << '\n';

 //創(chuàng)建三個線程,t1,t2,t3
 //形參作為拷貝, 引用計數(shù)也會加1
 std::thread t1(thr, p), t2(thr, p), t3(thr, p);
 std::cout << "Shared ownership between 3 threads and released\n"
 << "ownership from main:\n"
 << " p.get() = " << p.get()
 << ", p.use_count() = " << p.use_count() << '\n';
 //等待結(jié)束
 t1.join(); t2.join(); t3.join();
 std::cout << "All threads completed, the last one deleted\n";

 return 0;
}