update dir

using/derived_base.cpp

@@ -0,0 +1,48 @@
+#include <iostream>
+
+using namespace std;
+
+class Base1 {
+    public:
+        Base1():value(10) {}
+        virtual ~Base1() {}
+        void test1() { cout << "Base test1..." << endl; }
+    protected: // 保护
+        int value;
+};
+// 默认为私有继承
+class Derived1 : Base1 {
+    public:
+        void test2() { cout << "value is " << value << endl; }
+};
+
+class Base {
+    public:
+        Base():value(20) {}
+        virtual ~Base() {}
+        void test1() { cout << "Base test1..." << endl; }
+    protected:  //私有
+        int value;
+};
+
+/**
+ * 子类对父类成员的访问权限跟如何继承没有任何关系，
+ * “子类可以访问父类的public和protected成员，不可以访问父类的private成员”——这句话对任何一种继承都是成立的。
+ *
+ */
+class Derived : Base {
+    public:
+        using Base::value;
+        void test2() { cout << "value is " << value << endl; }
+};
+
+
+int main() 
+{
+    Derived1 d1;
+    d1.test2();
+
+    Derived d;
+    d.test2();
+    return 0;
+}