add classpermission

.vscode/settings.json

@@ -39,6 +39,7 @@
         "sstream": "cpp",
         "stdexcept": "cpp",
         "streambuf": "cpp",
-        "ctime": "cpp"
+        "ctime": "cpp",
+        "cstring": "cpp"
     }
 }

ClassPermission/CMakeLists.txt

@@ -0,0 +1,8 @@
+cmake_minimum_required(VERSION 3.10)
+set(CMAKE_CXX_COMPILER "g++")#设置C++编译器
+set(CMAKE_CXX_FLAGS "-g -Wall")
+
+set(CMAKE_CXX_STANDARD 17)        # 使用C++17标准
+
+PROJECT (proj CXX)
+ADD_EXECUTABLE(main main.cpp)

ClassPermission/main.cpp

@@ -0,0 +1,67 @@
+#include<iostream>
+
+class BaseClass{
+    private:  // 类内代码才能访问 
+        int age; 
+    protected:  // 
+        int level;
+    public:
+        int width, height;
+        void coutAge(){
+            std::cout << "age = " << age << std::endl;
+        }
+        void coutLevel(){
+            std::cout << "level = " << level << std::endl; 
+        }
+        void coutWH(){
+            std::cout << "width = " << width << "\nheight = " << height << std::endl;
+        }
+        BaseClass(){ 
+            age = 31;
+            level = 4; 
+            width = 4;
+            height = 5; 
+        }
+
+    // 声明友元函数, 不能直接在类内定义，只能在类内声明，在内外定义
+    // 友元函数不是这个类的成员变量，所以不受public等的影响
+    // 友元函数可以访问类的private成员变量 
+    friend void printAge(BaseClass bc);
+};
+
+// 将父类的所有成员都继承下来，创建派生类对象时，会创建一个新的内存储存这些继承的成员变量/函数
+class Son1 : public BaseClass{
+    public:
+        void coutAge2(){
+            // // 这里的age继承自基类，储存在派生类对象的内存中，但是由于其来自基类并且访问权限是private，所以无法直接访问，但可以通过继承来的基类的public函数访问
+            // std::cout << "coutAge2 func, age = " << age << std::endl; // 报错：member "BaseClass::age" (declared at line 5) is inaccessible
+
+
+            std::cout << "this is coutAge2 in Class Son1 " << std::endl; 
+            coutAge();
+        }
+
+};
+
+void printAge(BaseClass bc){
+    std::cout << "bc.age:" << bc.age << std::endl;
+}
+
+int main(){
+    // BaseClass bc();   // 这个容易和类声明混淆
+    // Son1 sn();
+
+
+    BaseClass bc;
+    Son1 sn; 
+
+
+    // std::cout << bc.age << std::endl;  //无法获取age 
+    // std::cout << sn.age << std::endl;  //基类中有private age，派生类中可以继承，但是无法直接访问
+
+
+    sn.coutAge(); 
+    sn.coutAge2();
+
+    return 0;
+}

array/2Darray.cpp

@@ -15,7 +15,8 @@ int main(){
 
 
     // int (*arr2)[3] = &arr1; // 报错： a value of type "int (*)[2][3]" cannot be used to initialize an entity of type "int (*)[3]". 
-    int (*arr2)[3] = &arr1[0]; // arr2 是一个`int (*)[3]`类型指针; arr1可以表示为二维数组，但是在使用`*`索引时arr1本质上来说也是`int (*)[3]`,即指向第一行的数组. 
+    // int (*arr2)[3] = arr1;   // 这种方式可以，没有报错，并且等价于`int (*arr2)[3] = &arr1[0];`
+    int (*arr2)[3] = &arr1[0]; // arr2 是一个`int (*)[3]`类型指针; arr1表示为二维数组，类型为int [2][3]，`&arr1`类型是`int (*)[2][3]`,也就是指向2x3int的指针(PA2_A3_i).
     for(int i = 0; i < 2; i ++){
         for (int j = 0; j < 3; j ++){
             std::cout << arr2[i][j] << " ";

array/3Darray.cpp

@@ -1,6 +1,11 @@
 # include<iostream>
 
 int main(){
-    std::cout << "3Darray equal to 2Darray" << std::endl;  
+    int arr1[2][3][4] = {0,1,2,3,4,5,6,7,8};
+    int (*arr2)[3][4] = &arr1[0];
+    int *arr3[6];
+    std::cout << typeid(&arr3).name() << std::endl; // PA6_Pi 指向shape为6的int*数组的指针
+    std::cout << typeid(arr3).name() << std::endl; // A6_Pi 指向shape为6的int*数组
+    std::cout << typeid(&arr1[0]).name() << std::endl; // PA3_A4_i  int (*)[3][4]
     return 0;
 }

refer/CMakeLists.txt

@@ -0,0 +1,12 @@
+cmake_minimum_required(VERSION 3.10)
+set(CMAKE_CXX_COMPILER "g++") #设置C++编译器
+set(CMAKE_CXX_FLAGS "-g -Wall")
+
+set(CMAKE_CXX_STANDARD 17)        # 使用C++17标准
+
+PROJECT (proj CXX)
+SET(SRC_LIST main.cpp)
+ADD_EXECUTABLE(main ${SRC_LIST})
+
+MESSAGE(STATUS "This is BINARY dir " ${HELLO_BINARY_DIR})
+MESSAGE(STATUS "This is SOURCE dir " ${HELLO_SOURCE_DIR})

refer/main.cpp

@@ -0,0 +1,22 @@
+#include <iostream> 
+
+// return 引用
+int& fun(){
+    static int qa = -111; 
+    std::cout << qa  << std::endl;
+    return qa; // 返回指向qa的引用
+}
+
+// return 值
+int fun2(){
+    static int qb = -111; 
+    std::cout << qb  << std::endl;
+    return qb; // 先拷贝qb的值到临时变量，随后return此临时变量到主函数
+}
+
+int main(){
+    fun() = 335;   
+    fun();
+    // int& a = 334;  // 引用a无法绑定int常量
+    return 0 ; 
+}

struct/CMakeLists.txt

@@ -0,0 +1,12 @@
+cmake_minimum_required(VERSION 3.10)
+set(CMAKE_CXX_COMPILER "g++") #设置C++编译器
+set(CMAKE_CXX_FLAGS "-g -Wall")
+
+set(CMAKE_CXX_STANDARD 17)        # 使用C++17标准
+
+PROJECT (proj CXX)
+SET(SRC_LIST main.cpp)
+ADD_EXECUTABLE(main ${SRC_LIST})
+
+MESSAGE(STATUS "This is BINARY dir " ${HELLO_BINARY_DIR})
+MESSAGE(STATUS "This is SOURCE dir " ${HELLO_SOURCE_DIR})

struct/main.cpp

@@ -0,0 +1,52 @@
+#include <iostream>
+#include <cstring>
+
+using namespace std;
+
+struct Books{
+    char title[50] = "Default Title";  // 默认title
+    char author[50];
+    char subject[100];
+    int book_id;
+};
+
+typedef struct Books Books; 
+
+typedef struct
+{
+   char  title[50];
+   char  author[50];
+   char  subject[100];
+   int   book_id;
+}defBooks;
+
+
+int main(){
+    Books Book1, Book2; 
+
+    // Book1 详述
+    strcpy( Book1.title, "Learn C++ Programming");
+    strcpy( Book1.author, "Chand Miyan"); 
+    strcpy( Book1.subject, "C++ Programming");
+    Book1.book_id = 6495407;
+
+    // Book2 详述
+    strcpy( Book2.title, "Telecom Billing");
+    strcpy( Book2.author, "Yakit Singha");
+    strcpy( Book2.subject, "Telecom");
+    Book2.book_id = 6495700;
+
+    // 输出 Book1 信息
+    std::cout << "Book 1 title : " << Book1.title <<std::endl;
+    std::cout << "Book 1 author : " << Book1.author <<std::endl;
+    std::cout << "Book 1 subject : " << Book1.subject <<std::endl;
+    std::cout << "Book 1 id : " << Book1.book_id <<std::endl;
+
+    // 输出 Book2 信息
+    std::cout << "Book 2 title : " << Book2.title <<std::endl;
+    std::cout << "Book 2 author : " << Book2.author <<std::endl;
+    std::cout << "Book 2 subject : " << Book2.subject <<std::endl;
+    std::cout << "Book 2 id : " << Book2.book_id <<std::endl;
+
+    return 0;
+}