C++ 名称空间详情

namespace Jack {
    double pail;                           // variable declaration
    void fetch();                          // function prototype
    int pal;                               // variable declaration
    struct Well {...}                      // structure declaration
}

namespace Jill {
    double bucket(double n) {...};         // variable declaration
    double fetch;                          // variable declaration
    int pal;                               // variable declaration
    struct Hill {...}                      // structure declaration
}

namespace Jill {
    char* goose(const char*);
}

namespace Jack {
    void fetch() {
        ...
    }
}

namespace Jill {
    double bucket(double n) { ... }
    double fetch;
}
char fetch;

int main() {
    using Jill::fetch     // using declaration
    double fetch;         // Error! Already have a local fetch
    cin >> fetch;         // read a value into Jill::fetch
    cin >> ::fetch;       // read a value into global fetch
}

#include <iOStream>
using namespace std;

 
// 在函数中使用using编译指令，将使其中的名称在函数中可用
int main() {
    using namespace jack;   // make names available in vorn()
}

using namespace jack
using namespace jill   // 二者空间中都有pal变量

pal = 4;               // which one? now have a conflict

namespace elements {
    namespace fire {
        int flame;
        ...
    }
    float water;
}

namespace myth {
    using Jill::fetch;
    using namespace elements;
    using std::count;
}

myth::fetch
Jill::fetch

using namespace myth;

/// 以上和下面两句等价
using namespace myth;
using namespace elements;

// 给命名空间创建别名
namespace MEF = myth::elements::fire;
using MEF::flame;

static int counts       //全局声明 static storage, internal linkage

/// 等价于
namespace {
    int counts          //  static storage, internal linkage
}