如何在类的头文件中定义const double？

Question

Inside the header file of my class, I am trying the following and getting compiler complaints: 在我的类的头文件中，我正在尝试以下并获得编译器投诉：

private:
    static const double some_double= 1.0;

How are you supposed to actually do this? 你怎么这么做呢？

Answer 1

In C++11, you can have non-integral constant expressions thanks to constexpr : 在C ++ 11中，由于constexpr ，你可以使用非整数常量表达式：

private:
    static constexpr double some_double = 1.0;

Answer 2

Declare it in the header, and initialize it in one compilation unit (the .cpp for the class is sensible). 在头文件中声明它，并在一个编译单元中初始化它（该类的.cpp是合理的）。

//my_class.hpp
private:
static const double some_double;

//my_class.cpp
const double my_class::some_double = 1.0;

Answer 3

I've worked around this issue by doing this: 我通过这样做解决了这个问题：

//my_class.hpp
const double my_double() const {return 0.12345;}

//in use
double some_double = my_class::my_double();

I got the idea from 我从中得到了这个想法

math::pi()