support bazel complie this project and format code.

practical_exercises/10_day_practice/day6/virtual_func/vis.cpp

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+/* 从基类继承的成员将访问到派生类版本.cpp */
+#include <iostream>
+using namespace std;
+class B {
+public:
+  void f() { g(); }
+  virtual void g() { cout << "B::g"; }
+};
+class D : public B {
+public:
+  void g() { cout << "D::g\n"; }
+};
+int main() {
+  D d;
+  d.f();
+  
+  return 0;
+}