C++ 11範圍和全局變量

Question

如何從內部作用域到達全局變量，給定以下代碼示例，如何從主函數和最內部作用域到達全局字符串X，還有一旦我們退出到主範圍或其他範圍，大多數內部範圍是可訪問的？

#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

全球範圍可以通過使用::x達成，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; 
} 

它給你：

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

的硬位實際上是進入中間範圍，如main scope當你在內部範圍。要做到這一點

一種方法是用引用：

#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"; 
    } 
} 

這給：

1a outer 

2a outer 
2b middle 

3a outer 
3b middle 
3c inner 

---

但是，正如好的建議，你會發現，你不會有任何地方在附近有很多問題，如果你：

• 以更智能的方式命名你的變量，以便避免衝突;和
• 避免像瘟疫全局變量:-)

而且，作爲在內部範圍的變量，它們不再是可一旦你離開是範圍，甚至與參考（您可以複製他們到一個更大範圍的變量，但這不同於訪問內部範圍變量）。