C inline初始化静态const char *

struct T
{
   static int x = 42;
   // ^ error: ISO C++ forbids in-class initialization of
   // non-const static member 'T::x'
};

但是,为方便起见,对常量进行了特殊的例外处理：

struct T
{
   static const int x = 42;
   // ^ OK
};

请注意,在大多数情况下,您仍然需要定义常量(在.cpp文件中将是最佳位置)：

const int T::x;

[C++11: 9.4.2/3]:] If a non-volatile const static data member is of integral or enumeration type,its declaration in the class definition can specify a brace-or-equal-initializer in which every initializer-clause that is an assignment-expression is a constant expression (5.19). A static data member of literal type can be declared in the class definition with the constexpr specifier; if so,its declaration shall specify a brace-or-equal-initializer in which every initializer-clause that is an assignment-expression is a constant expression. [ Note: In both these cases,the member may appear in constant expressions. —end note ] The member shall still be defined in a namespace scope if it is odr-used (3.2) in the program and the namespace scope definition shall not contain an initializer.

现在,您的成员不是int,甚至const char * const也不是“整数类型”：

struct T
{
   static const char* const str = "hi";
   // ^ error: 'constexpr' needed for in-class initialization of
   // static data member 'const char* const T::str' of non-integral type
};

但它是一个“字面型”;你的结果是,如果你这样写：

static constexpr const char* const xml_ID_TAG = "id";
//     ^^^^^^^^^             ^^^^^

你应该没问题.无论如何,这可能更有意义：你为什么要改变指针？