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About

This library provides basic_fixed_string class template to enable fixed-size std::array semantic with standard-like string semantic.

Features#

  • C++17 or higher
  • Header-only
  • Dependency-free
Warning

Dependencies can be added later to enable lower C++ standards support.

  • No dynamic allocations
  • constexpr as much as possible
  • Can be used as class non-type template parameter (since C++20)

Possible usages#

  • Make your own eDSL with C++20's class non-type template parameter feature#

CTRE library uses similar class to make regular expressions in C++ more easy to use:

std::optional<std::string_view> extract_number(std::string_view s) noexcept {    if (auto m = ctre::match<"[a-z]+([0-9]+)">(s)) {        return m.get<1>().to_view();    } else {        return std::nullopt;    }}

  • Make more concise APIs#

For example, before fixed_string if you needed to implement MD5 hash function, you'd write something like this:

std::string hash_md5(std::string_view string);

This solution has 2 downsides:

  • it can allocate
  • it can return a string that is not 16 bytes

With fixed_string these 2 problems are solved:

fixstr::fixed_string<16> hash_md5(std::string_view string);

  • Use in a free-standing environment#

Returning to the example with the hash function: the implementation with std::string as the return type has one more downside which is a consequence of possible allocations - it cannot be used in free-standing environments where is no dynamic memory.

Examples#

  • Construction
constexpr fixstr::fixed_string foo = "foo";
  • Concatenation
using namespace fixstr;constexpr fixed_string first = "Hello, ";constexpr fixed_string second = "World!";constexpr auto result = first + second; // "Hello, World!"
  • Comparison
using namespace fixstr;constexpr fixed_string first = "Hello, ";constexpr fixed_string second = "World!";static_assert(first == second); // falsestatic_assert(first != second); // truestatic_assert(first < second);  // truestatic_assert(first <= second); // truestatic_assert(first > second);  // false static_assert(first >= second); // falsestatic_assert(first <=> second != 0); // true
  • Non-type template parameter
template <fixstr::fixed_string Foo>void bar(){    static_assert(Foo == "foo"sv);}
void foo(){    bar<"foo">();}

Integration#

Since it's a header only library, you need just copy fixed_string.hpp to your project.

If you are using vcpkg on your project for external dependencies, then you can use the fixed-string package.

If you are using Conan on your project for external dependencies, then you can use the Conan recipe located in the root of the repository.

Compiler compatibility#

  • GCC >= 7.3
  • Clang >= 5
  • ICC >= 19.0.1
  • MSVC >= 14.28 / Visual Studio 2019 (I don't have access to older VS versions right now, so it can work on older versions too)

Using basic_fixed_string as class non-type template parameter full available in GCC >= 10 and VS 2019 16.9 or newer