From d49f1a848440b1ffbaeacdabd1412c3ad1dd6800 Mon Sep 17 00:00:00 2001
From: light-city <455954986@qq.com>
Date: Wed, 7 Aug 2019 14:36:00 +0800
Subject: [PATCH] update dir

---
 README.md                              |   1 +
 c_poly/README.md                       |   7 ++
 explicit/README.md                     |   6 ++
 explicit/{explict => explicit}         | Bin 9288 -> 9288 bytes
 explicit/{explict.cpp => explicit.cpp} |   0
 friend/README.md                       |  14 +++
 union/README.md                        |   6 ++
 using/README.md                        | 120 +++++++++++++++++++++++++
 using/derived_base                     | Bin 0 -> 15168 bytes
 using/derived_base.cpp                 |  48 ++++++++++
 using/using_derived                    | Bin 0 -> 9320 bytes
 using/using_derived.cpp                |  36 ++++++++
 using/using_global                     | Bin 0 -> 9296 bytes
 using/using_global.cpp                 |  45 ++++++++++
 using/using_typedef                    | Bin 0 -> 22024 bytes
 using/using_typedef.cpp                |  34 +++++++
 16 files changed, 317 insertions(+)
 rename explicit/{explict => explicit} (75%)
 rename explicit/{explict.cpp => explicit.cpp} (100%)
 create mode 100644 using/README.md
 create mode 100755 using/derived_base
 create mode 100644 using/derived_base.cpp
 create mode 100755 using/using_derived
 create mode 100644 using/using_derived.cpp
 create mode 100755 using/using_global
 create mode 100644 using/using_global.cpp
 create mode 100755 using/using_typedef
 create mode 100644 using/using_typedef.cpp

diff --git a/README.md b/README.md
index b70efaf..6e8ddf5 100644
--- a/README.md
+++ b/README.md
@@ -24,6 +24,7 @@
 - [x] [c实现c++多态那些事](./c_poly)
 - [x] [explicit那些事](./explicit)
 - [x] [friend那些事](./friend)
+- [x] [using那些事](./using)
 
 代码运行：
  全部在linux下用vim编写，使用gcc/g++调试！全部可正常运行！
diff --git a/c_poly/README.md b/c_poly/README.md
index 790eebe..ed91220 100644
--- a/c_poly/README.md
+++ b/c_poly/README.md
@@ -1,4 +1,11 @@
 # C实现C++的面向对象特性
+
+## 关于作者：
+
+个人公众号：
+
+![](../img/wechat.jpg)
+
 ## 1.C++实现案例
 
 C++中的多态:在C++中会维护一张虚函数表，根据赋值兼容规则，我们知道父类的指针或者引用是可以指向子类对象的。
diff --git a/explicit/README.md b/explicit/README.md
index 05dda6f..740b7b0 100644
--- a/explicit/README.md
+++ b/explicit/README.md
@@ -1,5 +1,11 @@
 # explicit(显式)关键字那些事
 
+## 关于作者：
+
+个人公众号：
+
+![](../img/wechat.jpg)
+
 - explicit 修饰构造函数时，可以防止隐式转换和复制初始化
 - explicit 修饰转换函数时，可以防止隐式转换，但按语境转换除外
 
diff --git a/explicit/explict b/explicit/explicit
similarity index 75%
rename from explicit/explict
rename to explicit/explicit
index 888e363d011400d15fd013a52ce83edebb45c046..ab3a4124b4c8e2fc61e774ca575ca55d4998cb7a 100755
GIT binary patch
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diff --git a/explicit/explict.cpp b/explicit/explicit.cpp
similarity index 100%
rename from explicit/explict.cpp
rename to explicit/explicit.cpp
diff --git a/friend/README.md b/friend/README.md
index 768b95c..64ba791 100644
--- a/friend/README.md
+++ b/friend/README.md
@@ -1,4 +1,11 @@
 # 友元函数与友元类
+
+## 关于作者：
+
+个人公众号：
+
+![](../img/wechat.jpg)
+
 ## 0.概述
 
 友元提供了一种 普通函数或者类成员函数 访问另一个类中的私有或保护成员 的机制。也就是说有两种形式的友元：
@@ -11,6 +18,13 @@
 
 缺点：破坏了类的封装性和数据的透明性。
 
+总结：
+- 能访问私有成员
+- 破坏封装性
+- 友元关系不可传递
+- 友元关系的单向性
+- 友元声明的形式及数量不受限制
+
 ## 1.友元函数
 
 在类声明的任何区域中声明，而定义则在类的外部。
diff --git a/union/README.md b/union/README.md
index 5811fb9..5421d42 100644
--- a/union/README.md
+++ b/union/README.md
@@ -1,5 +1,11 @@
 # UNION那些事
 
+## 关于作者：
+
+个人公众号：
+
+![](../img/wechat.jpg)
+
 联合（union）是一种节省空间的特殊的类，一个 union 可以有多个数据成员，但是在任意时刻只有一个数据成员可以有值。当某个成员被赋值后其他成员变为未定义状态。联合有如下特点：
 
 - 默认访问控制符为 public
diff --git a/using/README.md b/using/README.md
new file mode 100644
index 0000000..1e50179
--- /dev/null
+++ b/using/README.md
@@ -0,0 +1,120 @@
+# using那些事
+## 关于作者：
+
+个人公众号：
+
+![](../img/wechat.jpg)
+
+## 基本使用
+
+局部与全局using，具体操作与使用见下面案例：
+
+```c++
+#include <iostream>
+#define isNs1 1
+//#define isGlobal 2
+using namespace std;
+void func() 
+{
+    cout<<"::func"<<endl;
+}
+
+namespace ns1 {
+    void func()
+    {
+        cout<<"ns1::func"<<endl; 
+    }
+}
+
+namespace ns2 {
+#ifdef isNs1 
+    using ns1::func;    /// ns1中的函数
+#elif isGlobal
+    using ::func; /// 全局中的函数
+#else
+    void func() 
+    {
+        cout<<"other::func"<<endl; 
+    }
+#endif
+}
+
+int main() 
+{
+    /**
+     * 这就是为什么在c++中使用了cmath而不是math.h头文件
+     */
+    ns2::func(); // 会根据当前环境定义宏的不同来调用不同命名空间下的func()函数
+    return 0;
+}
+```
+完整代码见：[using_global.cpp](using_global.cpp)
+## 改变访问性
+
+```
+class Base{
+public:
+ std::size_t size() const { return n;  }
+protected:
+ std::size_t n;
+};
+class Derived : private Base {
+public:
+ using Base::size;
+protected:
+ using Base::n;
+};
+```
+
+类Derived私有继承了Base，对于它来说成员变量n和成员函数size都是私有的，如果使用了using语句，可以改变他们的可访问性，如上述例子中，size可以按public的权限访问，n可以按protected的权限访问。
+完整代码见：[derived_base.cpp](derived_base.cpp)
+## 函数重载
+
+在继承过程中，派生类可以覆盖重载函数的0个或多个实例，一旦定义了一个重载版本，那么其他的重载版本都会变为不可见。
+
+如果对于基类的重载函数，我们需要在派生类中修改一个，又要让其他的保持可见，必须要重载所有版本，这样十分的繁琐。
+
+```c++
+#include <iostream>
+using namespace std;
+
+class Base{
+    public:
+        void f(){ cout<<"f()"<<endl;
+        }
+        void f(int n){
+            cout<<"Base::f(int)"<<endl;
+        }
+};
+
+class Derived : private Base {
+    public:
+        using Base::f;
+        void f(int n){
+            cout<<"Derived::f(int)"<<endl;
+        }
+};
+
+int main()
+{
+    Base b;
+    Derived d;
+    d.f();
+    d.f(1);
+    return 0;
+}
+```
+如上代码中，在派生类中使用using声明语句指定一个名字而不指定形参列表，所以一条基类成员函数的using声明语句就可以把该函数的所有重载实例添加到派生类的作用域中。此时，派生类只需要定义其特有的函数就行了，而无需为继承而来的其他函数重新定义。
+
+完整代码见：[using_derived.cpp](using_derived.cpp)
+## 取代typedef
+
+C中常用typedef A B这样的语法，将B定义为A类型，也就是给A类型一个别名B
+
+对应typedef A B，使用using B=A可以进行同样的操作。
+
+```c++
+typedef vector<int> V1; 
+using V2 = vector<int>;
+```
+完整代码见：[using_typedef.cpp](using_typedef.cpp)
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diff --git a/using/derived_base.cpp b/using/derived_base.cpp
new file mode 100644
index 0000000..b25ec55
--- /dev/null
+++ b/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;
+}
diff --git a/using/using_derived b/using/using_derived
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diff --git a/using/using_derived.cpp b/using/using_derived.cpp
new file mode 100644
index 0000000..eb7b5ae
--- /dev/null
+++ b/using/using_derived.cpp
@@ -0,0 +1,36 @@
+/**
+ * @file using_derived.cpp
+ * @brief 函数重装
+ * @author 光城
+ * @version v1
+ * @date 2019-08-07
+ */
+
+#include <iostream>
+using namespace std;
+
+class Base{
+    public:
+        void f(){ cout<<"f()"<<endl;
+        }
+        void f(int n){
+            cout<<"Base::f(int)"<<endl;
+        }
+};
+
+class Derived : private Base {
+    public:
+        using Base::f;
+        void f(int n){
+            cout<<"Derived::f(int)"<<endl;
+        }
+};
+
+int main()
+{
+    Base b;
+    Derived d;
+    d.f();
+    d.f(1);
+    return 0;
+}
diff --git a/using/using_global b/using/using_global
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literal 0
HcmV?d00001

diff --git a/using/using_global.cpp b/using/using_global.cpp
new file mode 100644
index 0000000..b8fba2f
--- /dev/null
+++ b/using/using_global.cpp
@@ -0,0 +1,45 @@
+/**
+ * @file using_global.cpp
+ * @brief using各种使用
+ * @author 光城
+ * @version v1
+ * @date 2019-08-07
+ */
+
+#include <iostream>
+#define isNs1 1
+//#define isGlobal 2
+using namespace std;
+void func() 
+{
+    cout<<"::func"<<endl;
+}
+
+namespace ns1 {
+    void func()
+    {
+        cout<<"ns1::func"<<endl; 
+    }
+}
+
+namespace ns2 {
+#ifdef isNs1 
+    using ns1::func;    /// ns1中的函数
+#elif isGlobal
+    using ::func; /// 全局中的函数
+#else
+    void func() 
+    {
+        cout<<"other::func"<<endl; 
+    }
+#endif
+}
+
+int main() 
+{
+    /**
+     * 这就是为什么在c++中使用了cmath而不是math.h头文件
+     */
+    ns2::func(); // 会根据当前环境定义宏的不同来调用不同命名空间下的func()函数
+    return 0;
+}
diff --git a/using/using_typedef b/using/using_typedef
new file mode 100755
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diff --git a/using/using_typedef.cpp b/using/using_typedef.cpp
new file mode 100644
index 0000000..5807122
--- /dev/null
+++ b/using/using_typedef.cpp
@@ -0,0 +1,34 @@
+/**
+ * @file using_typedef.cpp
+ * @brief g++ -o using_typedef using_typedef.cpp -std=c++11
+ * 取代typedef，使用using来定义别名
+ * @author 光城
+ * @version v1
+ * @date 2019-08-07
+ */
+
+#include <iostream>
+#include <vector>
+using namespace std;
+
+typedef vector<int> V1;
+using V2 = vector<int>;
+
+
+int main() 
+{
+    int nums1[] = {1,2,3,4,5,6};
+    V1 vec1(nums1,nums1+sizeof(nums1)/sizeof(int));
+    int nums2[] = {5,7,6};
+    V2 vec2(nums2,nums2+sizeof(nums2)/sizeof(int));
+    
+    for(auto i:vec1)
+        cout<<i<<" ";
+    cout<<endl;
+
+    for(auto i:vec2)
+        cout<<i<<" ";
+    cout<<endl;
+
+    return 0;
+}