c++ - C++11/14 中的静态常量与 constexpr 成员字段？

Question

这些成员变量有什么区别:

struct my_class {
    static const int i = 0;
    static constexpr int j = 0;
};

如果我的理解是正确的，我可以同时使用 i和 j作为编译时间常数。也就是说，std::array<int, my_class::i>和 std::array<int,my_class::j>应该可以。

Answer 1

整数或枚举类型的成员没有区别(如您的示例)。对于所有其他类型，常量表达式 require constexpr :

an lvalue-to-rvalue conversion (4.1) unless it is applied to

• a non-volatile glvalue of integral or enumeration type that refers to a complete non-volatile const object with a preceding initialization, initialized with a constant expression, or […]
• a non-volatile glvalue that refers to a non-volatile object defined with constexpr, or that refers to a non-mutable sub-object of such an object, or […]