namespace命名空间是C++中一个非常重要的概念，本文实例展示了namespace的相关语法，供大家参考。具体如下：
本段测试代码包括如下内容：
(1) 如何访问namespace中声明的名称；
(2) namespace导致的相关冲突；
(3) namespace可嵌套；
(4) 可以在namespace中使用using声明和using编译命令；
(5) 未命名的namespace：其作用域为定义该namespace所在的声明区域。C++推荐用来替代static定义静态变量。
具体程序代码如下：
#include <iostream>
using namespace std;
namespace jerry{
int height;
int weight;
void showHeight();
string name;
}
//
namespace jerry{
void showHeight()
{
cout<<"Method 3: Jerry height: "<<height<<" kg"<<endl;
}
}
namespace elements
{
namespace fire
{
int flame;
using namespace jerry; //(4) can use 'using' in namespace define
using std::cout;
}
float water;
}
//(5) no name namespace
//其作用域为定义时所在的声明域，可用来替换static变量，这是C++标准推荐的行为
namespace {
string data;
}
void testFun();
int main()
{
cout<<"This code is to test namespace"<<endl;
/*not allowed to define namespace in code segment
//Error
namespace jerry{
int height;
int weight;
}
*/
//(1) To access the data in namespace
//Method 1: 作用域解析符
jerry::height = 165;
cout<<"Method 1: Jerry height: " << jerry::height <<" cm"<<endl;
//Method 2: using声明
using jerry::weight;
weight = 64;
cout<<"Method 2: Jerry weight: " << weight<<" kg"<<endl;
//Method 3: using编译指令：All the define data in namespace jerry can be access.
using namespace jerry;
showHeight();
//(2) about name conflict
{
jerry::name = "Jerry";
string name = "Tom";
//using jerry::name; Error
cout << "name: "<<name<<endl;
/*
This method will lead conflict with locall parameter
using jerry::name;
cout << "name: "<<name<<endl;
*/
cout << "name: "<<jerry::name<<endl;
using namespace jerry;
//局部变量会覆盖jerry命名空间的name定义
cout << "name: "<<name<<endl;
}
//(3) namespace can nest
elements::fire::flame = 2;
using namespace elements::fire;
//(5) no name namespace
//其作用域为定义时所在的声明域，可用来替换static变量，这是C++标准推荐的行为
data = "hello";
cout<<"No name namespace: data: " << data <<endl;
testFun();
}
void testFun()
{
/*not allowed to define namespace in code segment
//Error
namespace jerry{
int height;
int weight;
}
*/
//(5) no name namespace
data = "hello in function";
cout<<"No name namespace: data: " << data <<endl;
}
运行结果如下图所示：
