将字符串存储在constexpr结构中 [英] store a string in a constexpr struct

问题描述

是否可以将字符串存储在 constexpr 结构中:

Is it possible to store a string in a constexpr struct:

到目前为止，我只能提出:

So far I could only come up with:

struct A
{
    constexpr A(std::string_view n): m_name(n) {}   
    constexpr auto name(){ return m_name; }

    std::string_view m_name; // This might become dangling!!
} 

这显然是一个好主意，如果此类仅仅使用

which is cleary only a good idea if this class is only used like this

A a = {"Hello"};
constexpr A b = {"World"};

不是这样

auto makeA(std::string n) { return A{n}; }
A a = makeA("Hello"); // Dangling internal std::string_view

我需要 constexpr 在编译时构造该结构.是否可以在运行时使其更安全，因为使用 std :: string_view 却不是.

I need the constexpr to construct the struct at compile time. Is it possible to make this safer at run-time, because with std::string_view, its not.

推荐答案

您可以这样做:

template<typename Char, Char... Cs>
struct CharSeq
{
    static constexpr const Char s[] = {Cs..., 0}; // The unique address
};

// That template uses the extension
template<typename Char, Char... Cs>
constexpr CharSeq<Char, Cs...> operator"" _cs() {
    return {};
}

在在编译时进行字符串实习以进行分析，查看我的答案，如果有 MAKE_STRING 宏，您不能使用扩展名(实际上更冗长，并且对可接受的字符串长度进行硬编码限制).

See my answer from String-interning at compiletime for profiling to have MAKE_STRING macro if you cannot used the extension (Really more verbose, and hard coded limit for accepted string length).

然后

struct A
{
    template <char ... Cs> 
    constexpr A(CharSeq<char, Cs...>) : m_name(CharSeq<char, Cs...>::s) {}

    constexpr auto name(){ return m_name; }

    std::string_view m_name;
};

仅具有类似于以下内容的有效用法:

With only valid usages similar to:

A a = {"Hello"_cs};
constexpr A b = {"World"_cs};

这篇关于将字符串存储在constexpr结构中的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！