如何在头文件中定义 const static std::string?

2022-01-11 00:00:00 static header constants c++

我有一个类，我想存储一个静态 std::string，它要么是真正的 const，要么是通过 getter 有效的 const.

I have a class that I would like to store a static std::string that is either truly const or effectively const via a getter.

我尝试了几种直接方法
1.

I've tried a couple direct approaches
1. 

const static std::string foo = "bar";

2.

const extern std::string foo; //defined at the bottom of the header like so 
...//remaining code in header
};  //close header class declaration
std::string MyClass::foo = "bar"
/#endif // MYCLASS_H

我也试过了

3.

protected:
    static std::string foo;
public:
    static std::string getFoo() { return foo; }

这些方法分别因以下原因而失败:

These approaches fail for these reasons respectively:

  1. 错误:非文字类型的静态数据成员 const string MyClass::foo 的类内初始化
  2. 为 foo 指定的存储类 -- 它似乎不喜欢将 extern 与 const 或 static
  3. 我的代码的其他部分甚至 getter 函数的返回行都会产生许多未定义的引用"错误
  1. error: in-class initialization of static data member const string MyClass::foo of non-literal type
  2. storage class specified for foo -- it doesn't seem to like combining extern with const or static
  3. many 'undefined reference to' errors generated by other parts of my code and even the return line of the getter function

原因我希望在标头而不是源文件中声明.这是一个将被扩展的类，它的所有其他功能都是纯虚拟的，所以我目前除了这些变量之外没有其他理由拥有源文件.

The reason I would like to have the declaration within the header rather than source file. This is a class that will be extended and all its other functions are pure virtual so I currently have no other reason than these variables to have a source file.

那么如何做到这一点呢?

So how can this be done?

推荐答案

一种方法是定义一个内部有一个静态变量的方法.

One method would be to define a method that has a static variable inside of it.

例如:

class YourClass
{
public:

    // Other stuff...

    const std::string& GetString()
    {
        // Initialize the static variable
        static std::string foo("bar");
        return foo;
    }

    // Other stuff...
};

这只会初始化静态字符串一次，每次调用函数都会返回一个对变量的常量引用.对您的目的有用.

This would only initialize the static string once and each call to the function will return a constant reference to the variable. Useful for your purpose.

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