diff --git a/README.md b/README.md
index bf3d129..050db38 100644
--- a/README.md
+++ b/README.md
@@ -6,10 +6,11 @@
* Supports converting to any base between 2 and 36 inclusive
* No external dependencies, only includes `type_traits` for template parameter checking
* Supports custom character types, e.g. `to_string<123, 10, wchar_t>`
+* C++20: Supports floating-point-to-string conversion with `f_to_string`
**How to use:**
-This single header file provides a `to_string` utility, which may be used as below:
+The file `to_string.hpp` provides a `to_string` utility, which may be used as below:
```cpp
const char *number = to_string<2147483648999954564, 16>; // produces "1DCD65003B9A1884"
@@ -22,6 +23,13 @@ With `to_string`, all that will be found in program disassembly are the resultin
Try it [on Compiler Explorer](https://godbolt.org/z/T-MFoh).
+`f_to_string.hpp`, requiring C++20, provides an `f_to_string` utility for floating-point conversion:
+
+```cpp
+puts(f_to_string<3.1415926>); // Defaults to 5-point precision: "3.14159"
+puts(f_to_string<{3.1415926, 7}>); // Specify precision: "3.1415926"
+```
+
# How it works
The basic structure of `to_string` is shown below:
@@ -29,7 +37,7 @@ The basic structure of `to_string` is shown below:
```cpp
template
struct to_string_t {
- char_type buf[]; // Size selection explained later.
+ char_type buf[]; // Array size determination explained later.
constexpr to_string_t() {} // Converts the integer to a string stored in buf.
constexpr operator char_type *() {} // These allow for the object to be implicitly converted
constexpr operator const char_type *() {} // to a character pointer.
diff --git a/f_to_string.hpp b/f_to_string.hpp
new file mode 100644
index 0000000..8b91a90
--- /dev/null
+++ b/f_to_string.hpp
@@ -0,0 +1,90 @@
+/**
+ * f_to_string.hpp - Provides compile-time floating-point-to-string conversion.
+ * Written by Clyne Sullivan.
+ * https://github.com/tcsullivan/constexpr-to-string
+ */
+
+#ifndef TCSULLIVAN_F_TO_STRING_HPP_
+#define TCSULLIVAN_F_TO_STRING_HPP_
+
+struct f_to_string_double_wrapper {
+ long long int whole = 0;
+ long long int frac = 0;
+
+ constexpr f_to_string_double_wrapper(double v, int prec = 5) {
+ whole = static_cast(v);
+ v -= whole;
+ for (int i = 0; i < prec; i++)
+ v *= 10;
+ frac = static_cast(v);
+ }
+};
+
+/**
+ * @struct f_to_string_t
+ * @brief Provides the ability to convert a floating-point number to a string at compile-time.
+ * @tparam N Number to convert
+ */
+template
+class f_to_string_t {
+ char_type buf[([]() constexpr noexcept {
+ unsigned int len = 2;
+ if (N.whole <= 0) len++;
+ for (auto n = N.whole; n; len++, n /= 10);
+ if (N.frac == 0 || (N.whole == 0 && N.frac < 0)) len++;
+ for (auto n = N.frac; n; len++, n /= 10);
+ return len;
+ }())] = {};
+
+ public:
+ /**
+ * Constructs the object, filling `buf` with the string representation of N.
+ */
+ constexpr f_to_string_t() noexcept {
+ auto append = [](auto V, auto& ptr) {
+ if (V != 0) {
+ for (auto n = V; n; n /= 10)
+ *--ptr = (V < 0 ? -1 : 1) * (n % 10) + '0';
+ } else {
+ *--ptr = '0';
+ }
+ };
+
+ auto ptr = end();
+ *--ptr = '\0';
+ append(N.frac, ptr);
+ *--ptr = '.';
+ append(N.whole, ptr);
+ if (N.frac < 0 || N.whole < 0)
+ *--ptr = '-';
+ }
+
+ // Support implicit casting to `char *` or `const char *`.
+ constexpr operator char_type *() noexcept { return buf; }
+ constexpr operator const char_type *() const noexcept { return buf; }
+
+ constexpr auto size() const noexcept { return sizeof(buf) / sizeof(buf[0]); }
+ // Element access
+ constexpr auto data() noexcept { return buf; }
+ constexpr const auto data() const noexcept { return buf; }
+ constexpr auto& operator[](unsigned int i) noexcept { return buf[i]; }
+ constexpr const auto& operator[](unsigned int i) const noexcept { return buf[i]; }
+ constexpr auto& front() noexcept { return buf[0]; }
+ constexpr const auto& front() const noexcept { return buf[0]; }
+ constexpr auto& back() noexcept { return buf[size() - 1]; }
+ constexpr const auto& back() const noexcept { return buf[size() - 1]; }
+ // Iterators
+ constexpr auto begin() noexcept { return buf; }
+ constexpr const auto begin() const noexcept { return buf; }
+ constexpr auto end() noexcept { return buf + size(); }
+ constexpr const auto end() const noexcept { return buf + size(); }
+};
+
+/**
+ * Simplifies use of `f_to_string_t` from `f_to_string_t()` to `f_to_string`.
+ */
+template
+constexpr f_to_string_t f_to_string;
+
+#endif // TCSULLIVAN_F_TO_STRING_HPP_
+
diff --git a/to_string.hpp b/to_string.hpp
index 2d18589..63b52ab 100644
--- a/to_string.hpp
+++ b/to_string.hpp
@@ -18,27 +18,28 @@ constexpr auto digit_count = sizeof(digits) / sizeof(digits[0]);
* @tparam N Number to convert
* @tparam base Desired base, can be from 2 to 36
*/
-template, int> = 0,
std::enable_if_t<(base > 1 && base < digit_count), int> = 0>
-struct to_string_t {
+class to_string_t {
// The lambda calculates what the string length of N will be, so that `buf`
// fits to the number perfectly.
- char_type buf[([] {
+ char_type buf[([]() constexpr noexcept {
unsigned int len = N > 0 ? 1 : 2;
- for (auto n = N < 0 ? -N : N; n; len++, n /= base);
+ for (auto n = N; n; len++, n /= base);
return len;
}())] = {};
+ public:
/**
* Constructs the object, filling `buf` with the string representation of N.
*/
constexpr to_string_t() noexcept {
+ auto ptr = end();
+ *--ptr = '\0';
if (N != 0) {
- auto ptr = buf + sizeof(buf) / sizeof(buf[0]);
- *--ptr = '\0';
- for (auto n = N < 0 ? -N : N; n; n /= base)
- *--ptr = digits[n % base];
+ for (auto n = N; n; n /= base)
+ *--ptr = digits[(N < 0 ? -1 : 1) * (n % base)];
if (N < 0)
*--ptr = '-';
} else {
@@ -47,20 +48,30 @@ struct to_string_t {
}
// Support implicit casting to `char *` or `const char *`.
- constexpr operator char_type *() { return buf; }
- constexpr operator const char_type *() const { return buf; }
-
- // Support range-based for loops
- constexpr auto begin() { return buf; }
- constexpr auto begin() const { return buf; }
- constexpr auto end() { return buf + sizeof(buf) / sizeof(buf[0]); }
- constexpr auto end() const { return buf + sizeof(buf) / sizeof(buf[0]); }
+ constexpr operator char_type *() noexcept { return buf; }
+ constexpr operator const char_type *() const noexcept { return buf; }
+
+ constexpr auto size() const noexcept { return sizeof(buf) / sizeof(buf[0]); }
+ // Element access
+ constexpr auto data() noexcept { return buf; }
+ constexpr const auto data() const noexcept { return buf; }
+ constexpr auto& operator[](unsigned int i) noexcept { return buf[i]; }
+ constexpr const auto& operator[](unsigned int i) const noexcept { return buf[i]; }
+ constexpr auto& front() noexcept { return buf[0]; }
+ constexpr const auto& front() const noexcept { return buf[0]; }
+ constexpr auto& back() noexcept { return buf[size() - 1]; }
+ constexpr const auto& back() const noexcept { return buf[size() - 1]; }
+ // Iterators
+ constexpr auto begin() noexcept { return buf; }
+ constexpr const auto begin() const noexcept { return buf; }
+ constexpr auto end() noexcept { return buf + size(); }
+ constexpr const auto end() const noexcept { return buf + size(); }
};
/**
* Simplifies use of `to_string_t` from `to_string_t()` to `to_string`.
*/
-template
+template
constexpr to_string_t to_string;
-
+
#endif // TCSULLIVAN_TO_STRING_HPP_