add read-only version of data_vector() function

git-svn-id: http://www.openmesh.org/svnrepo/OpenMesh/trunk@1196 fdac6126-5c0c-442c-9429-916003d36597

src/OpenMesh/Core/Utils/Property.hh

@@ -171,13 +171,17 @@ public: // data access interface
 
     return &data_[0];
   }
-
-  /// Get reference to property vector (be careful, improper usage, e.g. resizing, may crash OpenMesh!!!)
-  vector_type& data_vector() {
-
-    return data_;
-  }
-
+
+  /// Get reference to property vector (be careful, improper usage, e.g. resizing, may crash OpenMesh!!!)
+  vector_type& data_vector() {
+    return data_;
+  }
+
+  /// Const access to property vector
+  const vector_type& data_vector() const {
+    return data_;
+  }
+
   /// Access the i'th element. No range check is performed!
   reference operator[](int _idx)
   {
@@ -335,13 +339,17 @@ public:
 
 
 public:
-
-  /// Get reference to property vector (be careful, improper usage, e.g. resizing, may crash OpenMesh!!!)
-  vector_type& data_vector() {
-
-    return data_;
-  }
-
+
+  /// Get reference to property vector (be careful, improper usage, e.g. resizing, may crash OpenMesh!!!)
+  vector_type& data_vector() {
+    return data_;
+  }
+
+  /// Const access to property vector
+  const vector_type& data_vector() const {
+    return data_;
+  }
+
   /// Access the i'th element. No range check is performed!
   reference operator[](int _idx)
   {