update

basic_content/friend/friend_class.cpp

@@ -0,0 +1,28 @@
+#include <iostream>
+
+using namespace std;
+
+class A
+{
+public:
+    A(int _a):a(_a){};
+    friend class B;
+private:
+    int a;
+};
+
+class B
+{
+public:
+    int getb(A ca) {
+        return  ca.a; 
+    };
+};
+
+int main() 
+{
+    A a(3);
+    B b;
+    cout<<b.getb(a)<<endl;
+    return 0;
+}