How Can I Concisely Declare Compile-Time Strings in C ?

Declaring Compile-Time Strings Concisley in C

Introduction
In C , declaring compile-time strings, which remain constant throughout compilation, can prove cumbersome. Traditional approaches require specifying a variadic sequence of characters:

using str = sequence<'H', 'e', 'l', 'l', 'o', ',', ' ', 'w', 'o', 'r', 'l', 'd', '!'>;

Existing Approaches: Challenges and Limitations
Ideally, declaring compile-time strings should be more straightforward, such as:

using str1 = sequence<"Hello, world!">;
constexpr auto str2 = "Hello, world!"_s;

However, these approaches face obstacles:

• Approach 1 requires an array with external linkage and complex implementation.
• Approach 2, using user-defined literals, is challenging due to the non-constexpr nature of the input parameter.
• Constexpr functions cannot accept non-constexpr arrays as parameters.

Solution: str_const Library
As of Scott Schurr's presentation at C Now 2012, the str_const library offers a convenient solution:

constexpr str_const my_string = "Hello, world!";
static_assert(my_string.size() == 13);
static_assert(my_string[4] == 'o');
constexpr str_const world(my_string, 7, 5);
static_assert(world == "world");

This solution provides benefits such as constexpr range checking and flexible substring retrieval, without the need for macros.

Update: C 17 and std::string_view
In C 17, std::string_view offers a similar solution:

constexpr std::string_view my_string = "Hello, world!";
static_assert(my_string.size() == 13);
static_assert(my_string[4] == 'o');
constexpr std::string_view world(my_string.substr(7, 5));
static_assert(world == "world");

This approach provides the following advantages:

• No need for custom libraries or macros.
• Range checking using .at() or .substr().
• Can be used as a const parameter type.

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