plug-in an allocator behind the new expression

new-expression-with-allocator.cc

@@ -0,0 +1,85 @@
+#include <cstdio>
+#include <memory>
+
+struct use_allocator_t {
+  explicit use_allocator_t() = default;
+};
+
+template <class A>
+void* operator new(size_t size, use_allocator_t, A a)
+{
+  using traits = std::allocator_traits<A>;
+  return traits::allocate(a, size);
+}
+
+template <class A>
+void* operator new[](size_t size, use_allocator_t, A a)
+{
+  using traits = std::allocator_traits<A>;
+  return traits::allocate(a, size);
+}
+
+template <class A>
+void operator delete(void* p, use_allocator_t, A a)
+{
+  using traits = std::allocator_traits<A>;
+  return traits::deallocate(a, p);
+}
+
+template <class A>
+void operator delete[](void* p, use_allocator_t, A a)
+{
+  using traits = std::allocator_traits<A>;
+  return traits::deallocate(a, static_cast<typename traits::pointer>(p), 0);
+}
+
+template <class T>
+struct barfing_allocator {
+
+  using value_type = T;
+
+  T* allocate(size_t size)
+  {
+    printf("allocate %lu\n", size);
+    return static_cast<T*>(::operator new(size));
+  }
+
+  void deallocate(T* p, size_t)
+  {
+    printf("deallocate\n");
+    return ::operator delete(p);
+  }
+
+};
+
+struct fail_halfway {
+  static size_t counter;
+  size_t idx;
+  fail_halfway()
+    : idx(++counter)
+  {
+    printf("I am %lu\n", idx);
+    if (idx == 5)
+      throw 42;
+  }
+  ~fail_halfway()
+  {
+    printf("%lu dying\n", idx);
+  }
+};
+
+size_t fail_halfway::counter = 0;
+
+int main()
+{
+
+  barfing_allocator<fail_halfway> a;
+
+  try {
+    new (use_allocator_t(), a) fail_halfway[10];
+  } catch(int) {
+    return 0;
+  }
+
+  return 1;
+}