prepare for c++17

code/5/5.1.cpp

@@ -0,0 +1,66 @@
+#include <iostream>
+#include <memory>
+
+void foo(std::shared_ptr<int> i)
+{
+    (*i)++;
+}
+
+
+//struct Base {
+//    Base() { std::cout << "  Base::Base()\n"; }
+//    ~Base() { std::cout << "  Base::~Base()\n"; }
+//};
+//
+//struct Subclass: public Base {
+//    Subclass() { std::cout << "  Subclass::Subclass()\n"; }
+//    ~Subclass() { std::cout << "  Subclass::~Subclass()\n"; }
+//};
+//
+//void thr(std::shared_ptr<Base> p)
+//{
+//    std::this_thread::sleep_for(std::chrono::seconds(1));
+//    std::shared_ptr<Base> lp = p; // 即使引用计数增加也是线程安全的
+//    {
+//        static std::mutex io_mutex;
+//        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()
+{
+    // auto pointer = new int(10); // 非法, 不允许直接赋值
+    // 构造了一个 std::shared_ptr
+    auto pointer = std::make_shared<int>(10);
+    auto pointer2 = pointer;    // 引用计数+1
+    auto pointer3 = pointer;    // 引用计数+1
+    
+    
+    foo(pointer);
+    std::cout << *pointer << std::endl; // 11
+    int *p = pointer.get();             // 这样不会增加引用计数
+    
+    std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
+    std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
+    std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
+
+    pointer2.reset();
+    std::cout << "reset pointer2:" << std::endl;
+    std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
+    std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
+    std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
+    
+    pointer3.reset();
+    std::cout << "reset pointer3:" << std::endl;
+    std::cout << "pointer.use_count() = " << pointer.use_count() << std::endl;
+    std::cout << "pointer2.use_count() = " << pointer2.use_count() << std::endl;
+    std::cout << "pointer3.use_count() = " << pointer3.use_count() << std::endl;
+    // std::cout << *pointer << std::endl; // 引用计数为0时, 非法访问
+    
+    
+    // 离开作用域前，pointer 会被析构，引用计数减为0, 从而释放内存
+    return 0;
+}