Cpp-learning/len2

#include <iostream>

using namespace std;

#if 0
int a = 10;    //全局变量
void test01()
{
    int a = 20;//局部变量

    cout << "局部变量a = " << a << endl;    //优先选择局部变量

    //::作用域运算符（C++独有）

    cout << "全局变量a = " << ::a << endl;   //取全局变量
}


//定义一个名字为A的命名空间（变量、函数）
namespace A {
    int a = 100;
}
namespace B {
    int a = 200;
}


void test02()
{
    //A::a a是属于A中的
    cout << "namespace A中的a = " << A::a << endl;  //100
    cout << "namespace B中的a = " << B::a << endl;  //200
}



namespace A {
    int a = 1000;
    namespace B {
        int a = 2000;
    }
}

void test03()
{
    cout << "A中的a = " << A::a << endl;
    cout << "B中的a = " << A::B::a << endl;
}


//将c添加到已有的命名空间A中
namespace A{
    int a = 100;
    int b = 200;
}
namespace A{
    int c = 300;
}

void test04()
{
    cout << "A中的c = " << A::c << endl;
}



namespace A{
    int a = 100;    //变量
    void func()
    {
        cout << "func遍历a = " <<a<<endl;
    }
}

void test05()
{
    //变量的使用
    cout << "A中的a = " << A::a << endl;
    //函数的使用
    A::func();
}



namespace A{
    int a = 100;

    void func();
}

void A::func()
{
    cout << "func遍历a = " << a << endl;
}
void funb()
{
    cout << "funb遍历a = " << A::a << endl;
}
void test06()
{
    A::func();
    funb();
}

#endif

namespace veryLongName{
    int a  = 10;
    void func()
    {
        cout << "hello namespace" << endl;
    }
}

void test()
{
    namespace shortName = veryLongName;
    cout << "veryLongName::a : " << shortName::a << endl;
    veryLongName::func();
    shortName::func();
}
int main()
{
    test();
    return 0;
}