update

2019-12-12 16:09:55 +08:00
parent 3ae20ae621
commit 4f149eec72
38 changed files with 1770 additions and 9 deletions
--- a/codingStyleIdioms/1_classInitializers/1.1_类之间嵌套.cpp
+++ b/codingStyleIdioms/1_classInitializers/1.1_类之间嵌套.cpp
@@ -0,0 +1,52 @@
+//
+// Created by light on 19-12-9.
+//
+
+#include <iostream>
+
+class Animal {
+public:
+    Animal() {
+        std::cout << "Animal() is called" << std::endl;
+    }
+
+    Animal(const Animal &) {
+        std::cout << "Animal (const Animal &) is called" << std::endl;
+    }
+
+    Animal &operator=(const Animal &) {
+        std::cout << "Animal & operator=(const Animal &) is called" << std::endl;
+        return *this;
+    }
+
+    ~Animal() {
+        std::cout << "~Animal() is called" << std::endl;
+    }
+};
+
+class Dog {
+public:
+    // 第一种： 使用初始化列表。
+    Dog(const Animal &animal) : __animal(animal) {
+        std::cout << "Dog(const Animal &animal) is called" << std::endl;
+    }
+    // 第二种：构造函数赋值来初始化对象。
+//    Dog(const Animal &animal) {
+//        __animal = animal;
+//        std::cout << "Dog(const Animal &animal) is called" << std::endl;
+//    }
+    ~Dog() {
+        std::cout << "~Dog() is called" << std::endl;
+    }
+
+private:
+    Animal __animal;
+};
+
+int main() {
+    Animal animal;
+    std::cout << std::endl;
+    Dog d(animal);
+    std::cout << std::endl;
+    return 0;
+}
--- a/codingStyleIdioms/1_classInitializers/1.2_无默认构造的继承.cpp
+++ b/codingStyleIdioms/1_classInitializers/1.2_无默认构造的继承.cpp
@@ -0,0 +1,43 @@
+//
+// Created by light on 19-12-9.
+//
+#include <iostream>
+class Animal {
+public:
+    Animal(int age) {
+        std::cout << "Animal(int age) is called" << std::endl;
+    }
+
+    Animal(const Animal & animal) {
+        std::cout << "Animal (const Animal &) is called" << std::endl;
+    }
+
+    Animal &operator=(const Animal & amimal) {
+        std::cout << "Animal & operator=(const Animal &) is called" << std::endl;
+        return *this;
+    }
+
+    ~Animal() {
+        std::cout << "~Animal() is called" << std::endl;
+    }
+
+};
+
+class Dog : Animal {
+public:
+    Dog(int age) : Animal(age) {
+        std::cout << "Dog(int age) is called" << std::endl;
+    }
+
+    ~Dog() {
+        std::cout << "~Dog() is called" << std::endl;
+    }
+};
+
+int main() {
+    Animal animal(10);
+    std::cout << std::endl;
+    Dog d(100);
+    std::cout << std::endl;
+    return 0;
+}
--- a/codingStyleIdioms/1_classInitializers/1.3_类中const数据成员、引用数据成员.cpp
+++ b/codingStyleIdioms/1_classInitializers/1.3_类中const数据成员、引用数据成员.cpp
@@ -0,0 +1,20 @@
+//
+// Created by light on 19-12-9.
+//
+
+#include <iostream>
+
+class Animal {
+public:
+    Animal(int age,std::string name):age_(age),name_(name) {
+        std::cout << "Animal(int age) is called" << std::endl;
+    }
+private:
+    int &age_;
+    const std::string name_;
+};
+
+int main() {
+    Animal animal(10,"hh");
+    return 0;
+}
--- a/codingStyleIdioms/1_classInitializers/README.md
+++ b/codingStyleIdioms/1_classInitializers/README.md
@@ -0,0 +1,211 @@
+# 初始化列表与赋值
+
+- const成员的初始化只能在构造函数初始化列表中进行
+- 引用成员的初始化也只能在构造函数初始化列表中进行
+- 对象成员（对象成员所对应的类没有默认构造函数）的初始化，也只能在构造函数初始化列表中进行
+
+## 类之间嵌套
+
+**第一种： 使用初始化列表。**
+
+
+```cpp
+class Animal {
+public:
+    Animal() {
+        std::cout << "Animal() is called" << std::endl;
+    }
+
+    Animal(const Animal &) {
+        std::cout << "Animal (const Animal &) is called" << std::endl;
+    }
+
+    Animal &operator=(const Animal &) {
+        std::cout << "Animal & operator=(const Animal &) is called" << std::endl;
+        return *this;
+    }
+
+    ~Animal() {
+        std::cout << "~Animal() is called" << std::endl;
+    }
+};
+
+class Dog {
+public:
+    Dog(const Animal &animal) : __animal(animal) {
+        std::cout << "Dog(const Animal &animal) is called" << std::endl;
+    }
+
+    ~Dog() {
+        std::cout << "~Dog() is called" << std::endl;
+    }
+
+private:
+    Animal __animal;
+};
+
+int main() {
+    Animal animal;
+    std::cout << std::endl;
+    Dog d(animal);
+    std::cout << std::endl;
+    return 0;
+}
+```
+
+运行结果：
+```cpp
+Animal() is called
+
+Animal (const Animal &) is called
+Dog(const Animal &animal) is called
+
+~Dog() is called
+~Animal() is called
+~Animal() is called
+```
+
+依次分析从上到下：
+
+main函数中`Animal animal;`调用默认构造。
+
+`Dog d(animal);`等价于：
+
+```
+Animal __animal = animal;
+```
+实际上就是调用了拷贝构造，因此输出了：
+```
+Animal (const Animal &) is called
+```
+再然后打印Dog的构造函数里面的输出。
+
+最后调用析构，程序结束。
+
+**第二种：构造函数赋值来初始化对象。**
+
+构造函数修改如下：
+```cpp
+Dog(const Animal &animal) {
+    __animal = animal;
+    std::cout << "Dog(const Animal &animal) is called" << std::endl;
+}
+```
+此时输出结果：
+```
+Animal() is called
+
+Animal() is called
+Animal & operator=(const Animal &) is called
+Dog(const Animal &animal) is called
+
+~Dog() is called
+~Animal() is called
+~Animal() is called
+```
+
+于是得出：
+
+当调用`Dog d(animal);`时，等价于：
+
+先定义对象，再进行赋值，因此先调用了默认构造，再调用=操作符重载函数。
+
+```cpp
+// 假设之前已经有了animal对象
+Animal __animal;
+__animal = animal;
+```
+
+> 小结
+
+通过上述我们得出如下结论：
+
+- **类中包含其他自定义的class或者struct，采用初始化列表，实际上就是创建对象同时并初始化**
+- **而采用类中赋值方式，等价于先定义对象，再进行赋值，一般会先调用默认构造，在调用=操作符重载函数。**
+
+## 无默认构造函数的继承关系中
+
+现考虑把上述的关系改为继承，并修改Animal与Dog的构造函数，如下代码：
+
+```cpp
+class Animal {
+public:
+    Animal(int age) {
+        std::cout << "Animal(int age) is called" << std::endl;
+    }
+
+    Animal(const Animal & animal) {
+        std::cout << "Animal (const Animal &) is called" << std::endl;
+    }
+
+    Animal &operator=(const Animal & amimal) {
+        std::cout << "Animal & operator=(const Animal &) is called" << std::endl;
+        return *this;
+    }
+
+    ~Animal() {
+        std::cout << "~Animal() is called" << std::endl;
+    }
+};
+
+class Dog : Animal {
+public:
+    Dog(int age) : Animal(age) {
+        std::cout << "Dog(int age) is called" << std::endl;
+    }
+
+    ~Dog() {
+        std::cout << "~Dog() is called" << std::endl;
+    }
+
+};
+```
+
+上述是通过初始化列表给基类带参构造传递参数，如果不通过初始化列表传递，会发生什么影响？
+
+去掉初始化列表
+```
+Dog(int age)  {
+    std::cout << "Dog(int age) is called" << std::endl;
+}
+```
+运行程序：
+
+```
+error: no matching function for call to ‘Animal::Animal()’
+```
+
+由于在Animal中没有默认构造函数，所以报错，遇到这种问题属于灾难性的，我们应该尽量避免，可以通过初始化列表给基类的构造初始化。
+
+
+## 类中const数据成员、引用数据成员
+
+特别是引用数据成员，必须用初始化列表初始化，而不能通过赋值初始化！
+
+例如：在上述的Animal中添加私有成员，并修改构造函数：
+```cpp
+class Animal {
+public:
+    Animal(int age,std::string name) {
+        std::cout << "Animal(int age) is called" << std::endl;
+    }
+private:
+    int &age_;
+    const std::string name_;
+};
+```
+
+报下面错误：
+
+```cpp
+error: uninitialized reference member in ‘int&’
+```
+
+应该改为下面：
+
+```cpp
+Animal(int age, std::string name) : age_(age), name_(name) {
+    std::cout << "Animal(int age) is called" << std::endl;
+}
+```
+
--- a/codingStyleIdioms/1_classInitializers/initializer.cpp
+++ b/codingStyleIdioms/1_classInitializers/initializer.cpp
@@ -0,0 +1,23 @@
+//
+// Created by light on 19-12-9.
+//
+
+#include <iostream>
+
+using namespace std;
+
+class A {
+public:
+    A(int a) : _a(a), _p(nullptr) {     // 初始化列表
+
+    }
+
+private:
+    int _a;
+    int *_p;
+};
+
+int main() {
+    A aa(10);
+    return 0;
+}