【C++知识点】namespace命名空间的使用

#include<iostream>
#include<string>
namespace China {
    float population = 14.1;  //单位：亿
    std::string capital = "北京";
}
namespace Japan {
    float population = 1.27;  //单位：亿
    std::string capital = "东京";
}
using namespace Japan;
int main() {
    std::cout << "首都：" << capital << std::endl;
    std::cout << "人口：" << population << std::endl;
    std::cout << "首都：" << China::capital << std::endl;
    std::cout << "人口：" << China::population << std::endl;
    system("pause");
    return 0;
}

#include<iostream>
#include<string>
namespace China {
    float population = 14.1;  //单位：亿
    std::string capital = "北京";
}
namespace Japan {
    float population = 1.27;  //单位：亿
    std::string capital = "东京";
}
//注意：没有namspace
//直接指定命名空间中的标识符，而不是整个域名
using China::capital;
using Japan::population;
int main() {
    std::cout << "首都：" << capital << std::endl;
    std::cout << "人口：" << population << std::endl;
    system("pause");
    return 0;
}

#include<iostream>
#include<string>
namespace China {
    float population = 14.1;  //单位：亿
    std::string capital = "北京";
}
namespace Japan {
    float population = 1.27;  //单位：亿
    std::string capital = "东京";
}
using namespace China;
using Japan::population;
int main() {
    std::cout << "首都：" << capital << std::endl;
    std::cout << "人口：" << population << std::endl;  //出错
    system("pause");
    return 0;
}

using namespace China;  //China命名空间中有population
using Japan::population;  //又单独声明了Japan中的population

......
int main(){
    std::cout << "首都：" << capital << std::endl;
    std::cout << "人口：" << Japan::population << std::endl;
    system("pause");
    return 0;
}