book: translation of ch05

Update #12

code/5/5.3.weak.ptr.cpp

@@ -0,0 +1,38 @@
+//
+// 5.3.weak.ptr.cpp
+// chapter 05 start pointers and memory management
+// modern c++ tutorial
+//
+// created by changkun at changkun.de
+// https://github.com/changkun/modern-cpp-tutorial
+//
+
+
+#include <iostream>
+#include <memory>
+
+class A;
+class B;
+
+class A {
+public:
+    std::shared_ptr<B> pointer;
+    ~A() {
+        std::cout << "A was destroied" << std::endl;
+    }
+};
+class B {
+public:
+    std::shared_ptr<A> pointer;
+    ~B() {
+        std::cout << "B was destroied" << std::endl;
+    }
+};
+int main() {
+    std::shared_ptr<A> a = std::make_shared<A>();
+    std::shared_ptr<B> b = std::make_shared<B>();
+    a->pointer = b;
+    b->pointer = a;
+    
+    return 0;
+}