在C ++中的局部和全局静态变量 [英] On local and global static variables in C++

问题描述

C ++ Primer说

每个局部静态变量在第一次
执行通过对象的定义之前被初始化。当函数结束时，局部静态变量
不会被销毁;

局部静态变量与全局静态变量不同吗？

  void foo（）{
 static int x = 0; 
 ++ x; 
 
 cout<< x<< endl; 
} 
 
 int main（int argc，char const * argv []）{
 foo（）; // 1 
 foo（）; // 2 
 foo（）; // 3 
 return 0; 
} 
  

与

比较

  static int x = 0; 
 
 void foo（）{
 ++ x; 
 
 cout<< x<< endl; 
} 
 
 int main（int argc，char const * argv []）{
 foo（）; // 1 
 foo（）; // 2 
 foo（）; // 3 
 return 0; 
} 
  

解决方案

p>

• 此名称只能在函数中访问，并且没有链接。

第二个区别可以用来避免 static intialisation order fiasco ，其中全局变量可以在初始化之前访问。通过用返回对本地静态变量的引用的函数替换全局变量，您可以保证在任何对它进行访问之前对其进行初始化。 （但是，仍然不能保证在访问它之前不会被破坏;如果你认为你需要一个全局可访问的变量，你仍然需要非常小心。参见链接以帮助解决此问题。）

C++ Primer says

Each local static variable is initialized before the first time execution passes through the object's definition. Local statics are not destroyed when a function ends; they are destroyed when program terminates.

Are local static variables any different from global static variables? Other then the location where they are declared, what else is different?

void foo () {   
    static int x = 0;
    ++x;

    cout << x << endl;
}

int main (int argc, char const *argv[]) {
    foo();  // 1
    foo();  // 2
    foo();  // 3
    return 0;
}

compare with

static int x = 0;

void foo () {   
    ++x;

    cout << x << endl;
}

int main (int argc, char const *argv[]) {
    foo();  // 1
    foo();  // 2
    foo();  // 3
    return 0;
}

解决方案

The differences are:

• The name is only accessible within the function, and has no linkage.
• It is initialised the first time execution reaches the definition, not necessarily during the program's initialisation phases.

The second difference can be useful to avoid the static intialisation order fiasco, where global variables can be accessed before they're initialised. By replacing the global variable with a function that returns a reference to a local static variable, you can guarantee that it's initialised before anything accesses it. (However, there's still no guarantee that it won't be destroyed before anything finishes accessing it; you still need to take great care if you think you need a globally-accessible variable. See the comments for a link to help in that situation.)

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