在C ++（98、11和14）中初始化静态数据成员的正确方法是什么？ [英] What is the correct way to initialize static data members in C++ (98, 11 and 14)
问题描述
在C ++中初始化 static 数据成员的正确方法是什么？我也对它从C ++ 98到C ++ 11到C ++ 14的变化感兴趣。
What is the right way to initialize static data members in C++? I'm also interested in how it has changed from C++98, to C++11 to C++14.
这里是一个例子：
// bufferedOutput.h
class BufferedOutput
{
// Static member declaration.
static long bytecount;
};
// bufferedOutput.cpp
long BufferedOutput::bytecount = 50;
还有其他方法可以初始化 static 数据
Are there other ways to initialize static data members?
推荐答案
规则始终如下：
-
整数或枚举类型的
const静态数据成员（SDM）可以在类中使用常量表达式进行初始化。
A
conststatic data member (SDM) of integral or enumeration type can be initialised in class with a constant expression.
A constexpr SDM必须在类中使用常量表达式进行初始化。
A constexpr SDM must be initialised in class with a constant expression.
C ++ 17在默认构造函数初始化每个成员时不再需要使用初始化程序。此外， constexpr SDM是隐式内联变量，这使它们的声明成为定义（现已弃用外部定义）。
C++17 no longer requires an initializer when the default constructor initialises every member. Also, constexpr SDMs are implicitly inline variables, which makes their declaration a definition (external definitions are now deprecated).
对于在两种语言中均有效的代码，C ++ 03和C ++ 11 +之间没有任何实质性改变。
Nothing has substantially changed between C++03 and C++11+ for code that is valid in both languages.
请注意，对于非内联的SDM，无论是否提供了初始化程序，类内声明都不是一种定义，并且必须对它们进行定义。
Note that for SDMs that are not inline, the in-class declaration is not a definition—regardless of whether an initializer is provided—and they must be defined if they are odr-used.
从C ++ 17开始，我们可以使您的SDM内联，从而使其类内声明成为定义：
As of C++17, we can make your SDM inline, which makes its in-class declaration a definition:
class BufferedOutput
{
static inline long bytecount = 50;
};
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