函数模板，将字符串文字转换为std :: array

Question

Is it possible to have a function template that'll take a "string literal" and return a std::array<char,N> equivalent to

 char array[] = "string literal";

?

I'm wrapping POSIX APIs and I'd like to have a mkstemp function template that'll take a string literal and return

std::pair<
 ModifiedLiteral //template turned into actual name (probably in std::array)
,FileFd_RW       //My fd wrapper
>;

without using the heap.

Answer 1

Yes, you can:

#include <array>
#include <functional>
#include <cstddef>

template <std::size_t N> std::array<char, N> parse_literal(const char (&lit)[N]) {
  std::array<char, N> arr;
  std::copy(lit, lit + N, arr.begin());

  return arr;
}

void foo() {
  parse_literal("This is my rifle, this is my gun");
}

Answer 2

If your compiler supports C++14 you could use std::index_sequence to craft a machinery that would copy the string literal in compile time:

template<std::size_t N, std::size_t... I>
constexpr 
std::array<char, N>
a2t_impl(char const (&str)[N], std::index_sequence<I...>) {
    return {str[I]...};
}

template<std::size_t N, typename Indices = std::make_index_sequence<N>>
constexpr 
std::array<char, N>
a2t(char const (&str)[N]) {
    return a2t_impl(str, Indices());
}

template<std::size_t N>
constexpr 
std::array<char, N> 
stringtoarray(char const (&str)[N]) {
  return a2t(str);
}

Live Demo