在C ++中定义静态成员 [英] Defining static members in C++

问题描述

我试图定义一个公共静态变量，如下所示：

  public：
 static int j = 0 ; //或任何其他值太多
  

我在这行上得到一个编译错误：ISO C ++ forbids

1. 为什么在C ++中不允许这样做？




2. 这意味着C ++中的静态变量

谢谢！

解决方案

（1。）为什么不允许在C ++中？

$ b b

从 Bjarne Stroustrup的C ++风格和技巧常见问题：类通常在头文件中声明，并且头文件通常包括在许多翻译单元中。然而，为了避免复杂的链接器规则，C ++要求每个对象都有唯一的定义。如果C ++允许需要在内存中作为对象存储的实体的类定义，那么该规则将被破坏。

（2。）为什么允许const成员
初始化？

[ dirkgently更好]

（3。）在C ++中，这意味着静态变量
不会在C中初始化为0

知道，只要你在.cpp中声明了静态成员var，如果没有指定，它将被初始化为零：

  // in some .cpp 
 int Test :: j; // j = int（）; 
  

I am trying to define a public static variable like this :

public :
         static int j=0;        //or any other value too

I am getting a compilation error on this very line : ISO C++ forbids in-class initialization of non-const static member `j'.

1. Why is it not allowed in C++ ?

2. Why are const members allowed to be initialized ?

3. Does this mean static variables in C++ are not initialized with 0 as in C?

Thanks !

解决方案

(1.) Why is it not allowed in C++ ?

From Bjarne Stroustrup's C++ Style and Technique FAQ: A class is typically declared in a header file and a header file is typically included into many translation units. However, to avoid complicated linker rules, C++ requires that every object has a unique definition. That rule would be broken if C++ allowed in-class definition of entities that needed to be stored in memory as objects.

(2.) Why are const members allowed to be initialized ?

[dirkgently said it better]

(3.) Does this mean static variables in C++ are not initialized with 0 as in C?

As far as I know, as long as you declare the static member var in a .cpp it will be zero-initialized if you don't specify otherwise:

// in some .cpp
int Test::j; // j = int();

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