问混合常量表达式声明和常量定义

EN

struct Foo
{
    static constexpr char s[] = "Hello world";
};

const char Foo::s[];

in.cpp:6:19: error: redeclaration ‘Foo::s’ differs in ‘constexpr’
 const char Foo::s[];
                   ^
in.cpp:3:27: error: from previous declaration ‘Foo::s’
     static constexpr char s[] = "Hello world";
                           ^
in.cpp:6:19: error: declaration of ‘constexpr const char Foo::s [12]’ outside of class is not definition [-fpermissive]
 const char Foo::s[];

‘constexpr’ needed for in-class initialization of static data member ‘const char Foo::s [12]’ of non-integral type [-fpermissive]