The index is not right when BaseTypePtr vs DerviceTypePtr

Author: wintel2014

C++/STL/vector_index/index.cpp

@@ -0,0 +1,34 @@
+#include <vector>
+#include <iostream>
+
+struct ITask {
+    long mI;
+}; 
+
+struct Task:public ITask
+{
+    long mT;
+    long mN;
+};
+
+int main()
+{
+    std::vector<long> letters {0,0,1,1, 3,2,3,4,5,6,7,8};
+    
+    long* pLong = &letters[4];
+    auto index = pLong-letters.data();
+    std::cout<<index<<std::endl;
+    
+    
+    Task t1, t2, t3, t4;
+    std::vector<Task> T;
+    T.push_back(t1);
+    T.push_back(t2);
+    T.push_back(t3);
+    T.push_back(t4);
+    
+    ITask* pTask = &T[2];
+    std::cout<<pTask-static_cast<ITask*>(T.data())<<std::endl;
+    std::cout<<static_cast<Task*>(pTask)-(T.data())<<std::endl;
+    
+}