Merge pull request #21 from kenluobo/add_weak_ptr_test_case

Add weak_ptr test case

cplusplus/stl/15_weak_ptr.cpp

@@ -0,0 +1,45 @@
+#include "test.h"
+
+//============================================================
+template <typename T> struct Node {
+  std::weak_ptr<Node> next;
+  T data;
+
+  explicit Node(const T &data) : data(data) {}
+};
+
+void test_weak_ptr() {
+  using IntNode = Node<int>;
+  const auto node1 = std::make_shared<IntNode>(IntNode(1));
+  const auto node2 = std::make_shared<IntNode>(IntNode(2));
+  out("node1->data = ", node1->data, "; ",
+      "node1->use_count = ", node1.use_count());
+  out("node2->data = ", node2->data, "; ",
+      "node2->use_count = ", node2.use_count());
+
+  out("============================");
+  node1->next = node2;
+  node2->next = node1;
+  out("node1->data = ", node1->data, "; ",
+      "node1->use_count = ", node1.use_count());
+  out("node2->data = ", node2->data, "; ",
+      "node2->use_count = ", node2.use_count());
+
+  out("============================");
+  if (const auto lck = node1->next.lock()) {
+    out("lck->data = ", lck->data, "; ", "lck->use_count = ", lck.use_count());
+    out("node1->data = ", node1->data, "; ",
+        "node1->use_count = ", node1.use_count());
+  }
+  out("node1->data = ", node1->data, "; ",
+      "node1->use_count = ", node1.use_count());
+}
+
+//============================================================
+void test() {
+  // todo
+  TEST(test_weak_ptr);
+}
+
+//============================================================
+int main() { test(); }