[FEATURE] Add to_chars overload for floating points.

include/seqan3/std/charconv

@@ -847,6 +847,8 @@ void from_chars(char const *, char const *, bool, int = 10) = delete;
 template <std::Integral value_type>
 inline std::to_chars_result to_chars(char * first, char * last, value_type value, int base) noexcept
 {
+    assert(first != nullptr);
+    assert(last != nullptr);
     assert(2 <= base && base <= 36);
     return seqan3::detail::to_chars_integral(first, last, value, base, is_signed<value_type>());
 }
@@ -856,9 +858,31 @@ inline std::to_chars_result to_chars(char * first, char * last, value_type value
 template <std::Integral value_type>
 inline std::to_chars_result to_chars(char * first, char * last, value_type value) noexcept
 {
+    assert(first != nullptr);
+    assert(last != nullptr);
     return seqan3::detail::to_chars_itoa(first, last, value, is_signed<value_type>());
 }
 
+//!\brief std::to_chars overload for floating point via a std::stringstream for default base = 10.
+//!\ingroup charconv
+template <seqan3::FloatingPoint floating_point_type>
+inline std::to_chars_result to_chars(char * first, char * last, floating_point_type value) noexcept
+{
+    assert(first != nullptr);
+    assert(last != nullptr);
+
+    std::ostringstream ss;
+    ss << value;
+    auto str = ss.str();
+
+    if (last - first < static_cast<std::ptrdiff_t>(str.size()))
+        return {last, std::errc::value_too_large};
+
+    std::copy(str.begin(), str.end(), first);
+
+    return {first + str.size(), std::errc{}};
+}
+
 // -----------------------------------------------------------------------------
 // from_chars for integral types
 // -----------------------------------------------------------------------------

test/unit/std/charconv_test.cpp

@@ -13,6 +13,10 @@
 #include <seqan3/std/charconv>
 #include <seqan3/std/concepts>
 
+// =============================================================================
+// std::from_chars for integral types
+// =============================================================================
+
 template <typename T>
 class integral_from_char_test: public ::testing::Test { };
 
@@ -220,14 +224,31 @@ TYPED_TEST(integral_from_char_test, hexadicimal_number)
     }
 }
 
-TYPED_TEST(integral_from_char_test, to_char)
+// =============================================================================
+// std::to_chars for integral types
+// =============================================================================
+
+TYPED_TEST(integral_from_char_test, to_chars)
+{
+    TypeParam val{120};
+    std::array<char, 10> buffer{};
+
+    auto res = std::to_chars(buffer.data(), buffer.data() + buffer.size(), val);
+
+    EXPECT_EQ(res.ptr, &buffer[3]);
+    EXPECT_EQ(res.ec, std::errc{});
+    EXPECT_EQ((std::string_view{buffer.data(), 3}), std::string_view{"120"});
+}
+
+TYPED_TEST(integral_from_char_test, to_chars_error)
 {
     TypeParam val{120};
-    char buffer[10];
+    std::array<char, 1> buffer{};
 
-        // buffer.clear();
-    [[maybe_unused]] auto res = std::to_chars(&buffer[0], &buffer[0] + sizeof(buffer), val);
+    auto res = std::to_chars(buffer.data(), buffer.data() + buffer.size(), val);
 
+    EXPECT_EQ(res.ptr, buffer.data() + buffer.size());
+    EXPECT_EQ(res.ec, std::errc::value_too_large);
 }
 
 // =============================================================================
@@ -483,3 +504,19 @@ TYPED_TEST(from_char_real_test, non_valid_strings)
         EXPECT_EQ(res.ec, std::errc::invalid_argument);
     }
 }
+
+// =============================================================================
+// std::to_chars for float, double and long double
+// =============================================================================
+
+TYPED_TEST(from_char_real_test, to_chars)
+{
+    TypeParam val{120.3};
+    std::array<char, 10> buffer{};
+
+    auto res = std::to_chars(buffer.data(), buffer.data() + buffer.size(), val);
+
+    EXPECT_EQ(res.ptr, &buffer[5]);
+    EXPECT_EQ(res.ec, std::errc{});
+    EXPECT_EQ((std::string_view{buffer.data(), 5}), std::string_view{"120.3"});
+}