标头c ++ 11中的C ++静态const字符串 [英] C++ static const string in header c++11

问题描述

我想编写一个提供有限的RTTI信息的类.

I'm wanting to write a class that provides limited RTTI information.

现在我想要的是这样的东西

Now what I want is something like this

template<typename T>
struct isGameComponent
{
   public:
   static_assert(false,"If a non-specialized version is created we have problems");
}

template<>
struct isGameComponent<Transform>
{
  public:
  static const char* COMPONENT_TYPE_NAME = "Transform";
  static const uint32_t COMPONENT_TYPE_ID = HashString("Transform"); //constexpr 
};

//Do this a lot more

我说我不能初始化字符串，因为它不是文字类型，但我收到了编译时错误.我只想保留此lib标头.那不可能吗?

I get a compile time error though saying I can't initialize the string as it is not a literal type. I was wanting to keep this lib header only. Is that impossible?

推荐答案

要仅将模块保留为标头，您可以使用以下几种选择:

To keep the module as header only you have several options:

• inline 函数返回值.
• 模板化的常量技巧.
• C ++ 11 constexpr 关键字.

• inline functions that return the values.
• the templated constant trick.
• C++11 constexpr keyword.

内联函数示例:

template<typename T>
struct IsGameComponent;

template<>
struct IsGameComponent<Transform>
{
    static
    auto componenTypeName()
        -> const char*
    { return "Transform"; }

    static
    auto componentTypeId()
        -> uint32_t
    {
        static uint32_t const theId = hashString("Transform");
        return the_id;
    }
};

---

模板化常量技巧的示例:

---

Example of the templated constant trick:

template<typename T>
struct IsGameComponent;

template< class Dummy_ >
struct C_IsGameComponent_Transform
{
    static char const* const componentTypeName;
    static uint32_t const componentTypeId;
};

template< class D >
char const* const C_IsGameComponent_Transform<D>::componentTypeName = "Transform";

template< class D >
uint32_t const C_IsGameComponent_Transform<D>::componentTypeId  = hashString( "Transform" );

template<>
struct IsGameComponent<Transform>
    : C_IsGameComponent_Transform<void>
{
    // Constants available here.
};

---

C ++ 11示例 constexpr (这要求 hashString 是 constexpr 函数):

template<typename T>
struct IsGameComponent;

template< class Dummy_ >
struct C_IsGameComponent_Transform
{
    static char const* constexpr componentTypeName = "Transform";
    static uint32_t constexpr componentTypeId = hashString( "Transform" );
};

使用此解决方案，您无法获取任何这些常量的地址.

With this solution you can't take the address of any of these constants.

免责声明:以上代码都没有在任何C ++编译器附近.

Disclaimer: none of the code above has been near any C++ compiler.

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