clyne/constexpr-to-string
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Merge pull request #3 from SecMeant/digits_array

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Removing magic constant from template param check
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Clyne 2020-06-29 15:17:38 -04:00 committed by GitHub
commit 6710f1e699
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2 changed files with 13 additions and 4 deletions
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4
README.md
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@ -56,11 +56,13 @@ The integer/string conversion is done using a simple method I learned over the y
(*Note: The below examples of code are not up-to-date, though they still give a general idea of how `to_string` works.*)
```cpp
constexpr char digits[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
constexpr to_string_t() {
auto ptr = buf + sizeof(buf) / sizeof(buf[0]);
*--ptr = '\0';
for (auto n = N < 0 ? -N : N; n; n /= base)
*--ptr = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"[n % base];
*--ptr = digits[n % base];
if (N < 0)
*--ptr = '-';
}

13
to_string.hpp
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@ -9,6 +9,11 @@
#include <type_traits>
namespace constexpr_to_string {
constexpr char digits[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
constexpr auto digit_count = sizeof(digits) / sizeof(digits[0]);
/**
* @struct to_string_t
* @brief Provides the ability to convert any integral to a string at compile-time.
@ -17,7 +22,7 @@
*/
template<auto N, int base, typename char_type,
std::enable_if_t<std::is_integral_v<decltype(N)>, int> = 0,
std::enable_if_t<(base > 1 && base < 37), int> = 0>
std::enable_if_t<(base > 1 && base < digit_count), int> = 0>
class to_string_t {
// The lambda calculates what the string length of N will be, so that `buf`
// fits to the number perfectly.
@ -36,7 +41,7 @@ class to_string_t {
*--ptr = '\0';
if (N != 0) {
for (auto n = N; n; n /= base)
*--ptr = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"[(N < 0 ? -1 : 1) * (n % base)];
*--ptr = digits[(N < 0 ? -1 : 1) * (n % base)];
if (N < 0)
*--ptr = '-';
} else {
@ -65,10 +70,12 @@ class to_string_t {
constexpr const auto end() const noexcept { return buf + size(); }
};
} // namespace constexpr_to_string
/**
* Simplifies use of `to_string_t` from `to_string_t<N>()` to `to_string<N>`.
*/
template<auto N, int base = 10, typename char_type = char>
constexpr to_string_t<N, base, char_type> to_string;
constexpr constexpr_to_string::to_string_t<N, base, char_type> to_string;
#endif // TCSULLIVAN_TO_STRING_HPP_