初始化私有静态成员 [英] Initializing private static members

问题描述

在C ++中初始化私有静态数据成员的最好方法是什么？我试过这个，但它给我怪异的链接器错误：

What is the best way to initialize a private, static data member in C++? I tried this but it gives me weird linker errors:

class foo
{
    private:
        static int i;
};

int foo::i = 0;

我猜这是因为我无法从类外部初始化一个私人成员。那么这是最好的方法是什么？

I'm guessing this is because I can't initialize a private member from outside the class. So what's the best way to do this?

推荐答案

类声明应该在头文件不共享）。

文件：foo.h

The class declaration should be in the header file (Or in the source file if not shared).
File: foo.h

class foo
{
    private:
        static int i;
};

但初始化应在源文件中。

文件：foo.cpp

But the initialization should be in source file.
File: foo.cpp

int foo::i = 0;

如果初始化在头文件中，那么包含头文件的每个文件将具有静态成员。因此，在链接阶段，您会得到链接器错误，因为初始化变量的代码将在多个源文件中定义。

If the initialization is in the header file then each file that includes the header file will have a definition of the static member. Thus during the link phase you will get linker errors as the code to initialize the variable will be defined in multiple source files.

注意： Matt Curtis：指出，如果静态成员变量是const int类型，则C ++允许简化上述操作（例如 int ， bool ， char ）。然后，您可以直接在头文件中的类声明中声明和初始化成员变量：

Note: Matt Curtis: points out that C++ allows the simplification of the above if the static member variable is of const int type (e.g. int, bool, char). You can then declare and initialize the member variable directly inside the class declaration in the header file:

class foo
{
    private:
        static int const i = 42;
};

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