Is There a More Convenient Way to Declare Compile-Time Strings in C ?

Declaring Compile-Time Strings Conveniently in C

Creating and manipulating strings during compile-time can be a useful tool in C . However, the current process of declaring compile-time strings is cumbersome, requiring the use of variadic sequences of characters. This begs the question: Is there a more convenient way to declare compile-time strings in C ?

Existing Approaches and Their Limitations

Ideally, we would like to declare compile-time strings with syntax such as:

using str1 = sequence<"Hello, world!">;

Alternatively, we could use user-defined literals:

constexpr auto str2 = "Hello, world!"_s;

However, the declared type of str2 lacks a constexpr constructor, and the user-defined literal approach is not feasible due to pointer-to-member complications. Additionally, attempting to use a constexpr function to achieve this runs into the issue of the array or string parameter not being a constexpr type.

Proposed Solution and Current Status

While there is no current proposal or language feature that specifically addresses the issue of convenient compile-time string declaration, Scott Schurr proposed the str_const utility at C Now 2012. This utility, although requiring constexpr capabilities, offers a very elegant solution, as seen below:

int main() {
    constexpr str_const my_string = "Hello, world!";
    static_assert(my_string.size() == 13);
    static_assert(my_string[4] == 'o');
    constexpr str_const my_other_string = my_string;
    static_assert(my_string == my_other_string);
    constexpr str_const world(my_string.substr(7, 5));
    static_assert(world == "world");
//  constexpr char x = world[5]; // Does not compile because index is out of range!
}

C 17 Update

With the introduction of std::string_view in C 17, a better alternative to str_const is available. The code above can be rewritten as follows:

#include <string_view>

int main() {
    constexpr std::string_view my_string = "Hello, world!";
    static_assert(my_string.size() == 13);
    static_assert(my_string[4] == 'o');
    constexpr std::string_view my_other_string = my_string;
    static_assert(my_string == my_other_string);
    constexpr std::string_view world(my_string.substr(7, 5));
    static_assert(world == "world");
//  constexpr char x = world.at(5); // Does not compile because index is out of range!
}

This approach provides both compile-time string manipulation capabilities and out-of-range checks.

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