restructure and add ipi texs

ws2019/ipi/uebungen/cpp_headers/Ptr.hh

@@ -0,0 +1,55 @@
+template<class T>
+class Ptr {
+  struct RefCntObj {
+    int count;
+    T* obj;
+    RefCntObj (T* q) { count = 1; obj = q; }
+  };
+  RefCntObj* p;
+    
+  void report () {
+    std::cout << "refcnt = " << p->count << std::endl;
+  }
+  void increment () {
+    p->count = p->count + 1;
+    report();
+  }
+  void decrement () {
+    p->count = p->count - 1;
+    report();
+    if (p->count==0) {
+      delete p->obj; // Geht nicht fuer Felder!
+      delete p;
+    }
+  }
+
+public:
+  Ptr () { p=0; }
+
+  Ptr (T* q) {
+    p = new RefCntObj(q);
+    report();
+  }
+
+  Ptr (const Ptr<T>& y) {
+    p = y.p;
+    if (p!=0) increment();
+  }
+
+  ~Ptr () {
+    if (p!=0) decrement();
+  }
+
+  Ptr<T>& operator= (const Ptr<T>& y) {
+    if (p!=y.p) {
+      if (p!=0) decrement();
+      p = y.p;
+      if (p!=0) increment();
+    }
+    return *this;
+  }
+
+  T& operator* () { return *(p->obj); }
+
+  T* operator-> () { return p->obj; }
+};