local class and nested class

• local class
  在一个函数里面声明的类从属于那个函数。比如说

void fun() {
    class base {
    private:
    public:
    };
}

local class 仅仅能够在函数内部声明对象

void fun() {
    class base {
    private:
        int i;
    public:
        base() { cout << "1" << endl; }
        void print() {
            cout << "2" << endl;
        }
    };
    base a;
    a.print();
}
int main() {
    base a;
    return 0;
}

local class 里面的函数仅仅能够在函数内部定义

void fun(){
    class base {
    private:
        int i;
    public:
        base() { cout << "1" << endl; }
        void print() { 
            cout << "2" << endl;
        }
    };
    base a;
    a.print();
}
int main() {
    fun();
    return 0;
}

---

void fun() {
    class base {
    private:
        int i;
    public:
        base() { cout << "1" << endl; }
        void print();
    };
    void base::print() {
        cout << "2" << endl;
    }
    base a;
    a.print();
}
int main() {
    fun();
    return 0;
}

局部类不能定义静态变量，但可以定义静态函数

void fun() {
    class base {
    private:
        int i;
    public:
        static int m;
        void print() {
            cout << "2" << endl;
        }
    };
    base a;
    a.print();
}

static int i2;
void fun() {
    class base {
    private:
        int i;
    public:
        static void print() {
            i2++;
            cout << i2 << endl;
        }
    };
    base a;
    a.print();
}
int main() {
    i2++;
    fun();
    return 0;
}

局部类仅仅能够访问本函数里或全局静态变量或者枚举量

void fun() {
    static int i2;
    enum tem
    {
        x=0,y=0
    };
    class base {
    private:
        int i;
    public:
        static void print() {
            cout << "i2=" <"x=" << x << endl;
        }
    };
    base a;
    a.print();
}
int main() {
    //i2++;
    fun();
    return 0;
}

void fun() {
    int x;
    class base {
    private:
        int i;
    public:
        void print() {
            cout << "x=" << x << endl;
        }
    };
    base a;
    a.print();
}

局部变量可以访问全局变量，全局函数，还能够访问函数内部其他类

int x=2;
void fun() {

    class base1 {
    private:

    public:int i=1;
        void print() {
            cout << "x=" << x << endl;
        }
    };
    class base2 :public base1{
    private:
        int i;
    public:
        void print() {
            cout << "base::i =" << base1::i << endl;
            cout << "x=" << x << endl;
        }
    };
    base2 a;
    a.print();
}
int main() {
    //i2++;
    fun();
    return 0;
}

• nested class

nested class是指在一个已经存在的类中定义的类，假设在A中定义了B，那么B就是nested class。
这其中，有如下规则：
B可以改变A成员值；
A不可以改变B成员值。

B可以改变A成员值

class base1 {
private:
    int i;
    class base2 {
    private:
        int i2;
    public:
        base2(int i1) :i2(i1) {}
        void print(base1 *s) {
            cout << "---" << s->i << endl;
        }
    };
public:
    base1(int i1) :i(i1) {}
    void print() {
        cout << "---" << i << endl;
    }
};

A不可以改变B成员值

class base3{
private:
    int i;
    class base2 {
    private:
        int i2;
    public:
        base2(int i1) :i2(i1) {}
    };
public:
    base3(int i1) :i(i1) {}
    void print(base2 *s) {
        cout << "---" << s->i2 << endl;
    }
};