C++ 11范围和全局变量

Question

如何从内部作用域到达全局变量，给定以下代码示例，如何从主函数和最内部作用域到达全局字符串X，还有一旦我们退出到主范围或其他范围，大多数内部范围是可访问的？

#include <iostream> 
#include <string> 
std::string x = "global"; 
int counter = 1; 

int main() 
{ 
    std::cout <<counter ++ << " " << x << std::endl; 
    std::string x = "main scope"; 
    std::cout <<counter ++ << " " << x << std::endl; 
    { 
     std::cout <<counter ++ << " " << x << std::endl; 
     std::string x = "inner scope"; 
     std::cout <<counter ++ << " " << x << std::endl; 
    } 
    std::cout <<counter++ << " " << x << std::endl; 
} 

的COUT目前是：

1 global 
2 main scope 
3 main scope 
4 inner scope 
5 main scope 

Answer 1

全球范围可以通过使用::x达成，按：

#include <iostream> 
#include <string> 

std::string x = "global"; 
int counter = 1; 

int main() 
{ 
    std::cout << counter++ << " " << x << std::endl; 
    std::string x = "main scope"; 
    std::cout << " " << ::x << std::endl; 
    std::cout << counter++ << " " << x << std::endl; 
    { 
     std::cout << " " << ::x << std::endl; 
     std::cout << counter++ << " " << x << std::endl; 
     std::string x = "inner scope"; 
     std::cout << " " << ::x << std::endl; 
     std::cout << counter++ << " " << x << std::endl; 
    } 
    std::cout << " " << ::x << std::endl; 
    std::cout << counter++ << " " << x << std::endl; 
} 

它给你：

1 global 
    global 
2 main scope 
    global 
3 main scope 
    global 
4 inner scope 
    global 
5 main scope 

的硬位实际上是进入中间范围，如main scope当你在内部范围。要做到这一点

一种方法是用引用：

#include <iostream> 
#include <string> 

std::string x = "outer"; 

int main() 
{ 
    std::cout << "1a " << x << "\n\n"; 

    std::string x = "middle"; 
    std::cout << "2a " << ::x << '\n'; 
    std::cout << "2b " << x << "\n\n"; 

    { 
     std::string &midx = x; // make ref to middle x. 
     std::string x = "inner"; // hides middle x. 
     std::cout << "3a " << ::x << '\n'; 
     std::cout << "3b " << midx << '\n'; // get middle x via ref. 
     std::cout << "3c " << x << "\n\n"; 
    } 
} 

这给：

1a outer 

2a outer 
2b middle 

3a outer 
3b middle 
3c inner 

---

但是，正如好的建议，你会发现，你不会有任何地方在附近有很多问题，如果你：

• 以更智能的方式命名你的变量，以便避免冲突;和
• 避免像瘟疫全局变量:-)

而且，作为在内部范围的变量，它们不再是可一旦你离开是范围，甚至与参考（您可以复制他们到一个更大范围的变量，但这不同于访问内部范围变量）。