添加 'len2'

len2

@@ -0,0 +1,126 @@
+#include <iostream>
+
+using namespace std;
+
+#if 0
+int a = 10;    //全局变量
+void test01()
+{
+    int a = 20;//局部变量
+
+    cout << "局部变量a = " << a << endl;    //优先选择局部变量
+
+    //::作用域运算符（C++独有）
+
+    cout << "全局变量a = " << ::a << endl;   //取全局变量
+}
+
+
+//定义一个名字为A的命名空间（变量、函数）
+namespace A {
+    int a = 100;
+}
+namespace B {
+    int a = 200;
+}
+
+
+void test02()
+{
+    //A::a a是属于A中的
+    cout << "namespace A中的a = " << A::a << endl;  //100
+    cout << "namespace B中的a = " << B::a << endl;  //200
+}
+
+
+
+namespace A {
+    int a = 1000;
+    namespace B {
+        int a = 2000;
+    }
+}
+
+void test03()
+{
+    cout << "A中的a = " << A::a << endl;
+    cout << "B中的a = " << A::B::a << endl;
+}
+
+
+//将c添加到已有的命名空间A中
+namespace A{
+    int a = 100;
+    int b = 200;
+}
+namespace A{
+    int c = 300;
+}
+
+void test04()
+{
+    cout << "A中的c = " << A::c << endl;
+}
+
+
+
+namespace A{
+    int a = 100;    //变量
+    void func()
+    {
+        cout << "func遍历a = " <<a<<endl;
+    }
+}
+
+void test05()
+{
+    //变量的使用
+    cout << "A中的a = " << A::a << endl;
+    //函数的使用
+    A::func();
+}
+
+
+
+namespace A{
+    int a = 100;
+
+    void func();
+}
+
+void A::func()
+{
+    cout << "func遍历a = " << a << endl;
+}
+void funb()
+{
+    cout << "funb遍历a = " << A::a << endl;
+}
+void test06()
+{
+    A::func();
+    funb();
+}
+
+#endif
+
+namespace veryLongName{
+    int a  = 10;
+    void func()
+    {
+        cout << "hello namespace" << endl;
+    }
+}
+
+void test()
+{
+    namespace shortName = veryLongName;
+    cout << "veryLongName::a : " << shortName::a << endl;
+    veryLongName::func();
+    shortName::func();
+}
+int main()
+{
+    test();
+    return 0;
+}