Move get_rcl_allocator to the rclcpp namespace.

Author: stevewolter

demo_nodes_cpp/src/topics/allocator_tutorial.cpp

@@ -92,7 +92,9 @@ constexpr bool operator!=(
   return false;
 }
 
-// You need to overload get_rcl_allocator for custom allocators.
+namespace rclcpp {
+
+// You need to overload rclcpp::get_rcl_allocator for custom allocators.
 // This function needs to build an instance of rcl_allocator_t
 // for use in C code.
 template<typename T>
@@ -119,6 +121,8 @@ rcl_allocator_t get_rcl_allocator(MyAllocator<T>)
   return rcl_allocator;
 }
 
+}  // namespace rclcpp
+
 // Override global new and delete to count calls during execution.
 
 static bool is_running = false;