Add string and string_view interfaces to from_chars

doc/decimal/charconv.adoc

@@ -88,6 +88,18 @@ namespace decimal {
 template <typename DecimalType>
 constexpr boost::decimal::from_chars_result from_chars(const char* first, const char* last, DecimalType& value, boost::decimal::chars_format fmt = boost::decimal::chars_format::general) noexcept
 
+#ifdef BOOST_DECIMAL_HAS_STD_STRING_VIEW
+
+template <typename DecimalType>
+constexpr boost::decimal::from_chars_result from_chars(std::string_view str, DecimalType& value, boost::decimal::chars_format fmt = boost::decimal::chars_format::general) noexcept
+
+#else
+
+template <typename DecimalType>
+constexpr boost::decimal::from_chars_result from_chars(const std::string& str, DecimalType& value, boost::decimal::chars_format fmt = boost::decimal::chars_format::general) noexcept
+
+#endif
+
 #ifdef BOOST_DECIMAL_HAS_STD_CHARCONV
 
 template <typename DecimalType>

doc/decimal/config.adoc

@@ -46,3 +46,5 @@ This flag increases the performance of the basis operations (e.g. add, sub, mul,
 - `BOOST_DECIMAL_HAS_STD_CHARCONV`: This macro is defined if header `<charconv>` exists and the language standard used is >= C++17
   * We only need the structs and enums out of the header so we are not concerned with being overly restrictive about the feature test macros.
     ** Known compilers that support this lighter  requirement are: GCC >= 10, Clang >= 13, and MSVC >= 14.2
+
+- `BOOST_DECIMAL_HAS_STD_STRING_VIEW`: This macro is defined if header `<string_view>` exists and the langauge standard used is >= C++17

include/boost/decimal/charconv.hpp

@@ -27,6 +27,10 @@
 
 #if !defined(BOOST_DECIMAL_DISABLE_CLIB)
 
+#ifndef BOOST_DECIMAL_BUILD_MODULE
+#include <string>
+#endif
+
 namespace boost {
 namespace decimal {
 
@@ -94,31 +98,103 @@ BOOST_DECIMAL_EXPORT constexpr auto from_chars(const char* first, const char* la
     return detail::from_chars_general_impl(first, last, value, fmt);
 }
 
+#ifndef BOOST_DECIMAL_HAS_STD_STRING_VIEW
+BOOST_DECIMAL_EXPORT inline auto from_chars(const std::string& str, decimal32& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#else
+BOOST_DECIMAL_EXPORT constexpr auto from_chars(std::string_view str, decimal32& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#endif
+
 BOOST_DECIMAL_EXPORT constexpr auto from_chars(const char* first, const char* last, decimal32_fast& value, chars_format fmt = chars_format::general) noexcept
 {
     return detail::from_chars_general_impl(first, last, value, fmt);
 }
 
+#ifndef BOOST_DECIMAL_HAS_STD_STRING_VIEW
+BOOST_DECIMAL_EXPORT inline auto from_chars(const std::string& str, decimal32_fast& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#else
+BOOST_DECIMAL_EXPORT constexpr auto from_chars(std::string_view str, decimal32_fast& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#endif
+
 BOOST_DECIMAL_EXPORT constexpr auto from_chars(const char* first, const char* last, decimal64& value, chars_format fmt = chars_format::general) noexcept
 {
     return detail::from_chars_general_impl(first, last, value, fmt);
 }
 
+#ifndef BOOST_DECIMAL_HAS_STD_STRING_VIEW
+BOOST_DECIMAL_EXPORT inline auto from_chars(const std::string& str, decimal64& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#else
+BOOST_DECIMAL_EXPORT constexpr auto from_chars(std::string_view str, decimal64& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#endif
+
 BOOST_DECIMAL_EXPORT constexpr auto from_chars(const char* first, const char* last, decimal64_fast& value, chars_format fmt = chars_format::general) noexcept
 {
     return detail::from_chars_general_impl(first, last, value, fmt);
 }
 
+#ifndef BOOST_DECIMAL_HAS_STD_STRING_VIEW
+BOOST_DECIMAL_EXPORT inline auto from_chars(const std::string& str, decimal64_fast& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#else
+BOOST_DECIMAL_EXPORT constexpr auto from_chars(std::string_view str, decimal64_fast& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#endif
+
 BOOST_DECIMAL_EXPORT constexpr auto from_chars(const char* first, const char* last, decimal128& value, chars_format fmt = chars_format::general) noexcept
 {
     return detail::from_chars_general_impl(first, last, value, fmt);
 }
 
+#ifndef BOOST_DECIMAL_HAS_STD_STRING_VIEW
+BOOST_DECIMAL_EXPORT inline auto from_chars(const std::string& str, decimal128& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#else
+BOOST_DECIMAL_EXPORT constexpr auto from_chars(std::string_view str, decimal128& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#endif
+
 BOOST_DECIMAL_EXPORT constexpr auto from_chars(const char* first, const char* last, decimal128_fast& value, chars_format fmt = chars_format::general) noexcept
 {
     return detail::from_chars_general_impl(first, last, value, fmt);
 }
 
+#ifndef BOOST_DECIMAL_HAS_STD_STRING_VIEW
+BOOST_DECIMAL_EXPORT inline auto from_chars(const std::string& str, decimal128_fast& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#else
+BOOST_DECIMAL_EXPORT constexpr auto from_chars(std::string_view str, decimal128_fast& value, chars_format fmt = chars_format::general) noexcept
+{
+    return detail::from_chars_general_impl(str.data(), str.data() + str.size(), value, fmt);
+}
+#endif
+
 #ifdef BOOST_DECIMAL_HAS_STD_CHARCONV
 BOOST_DECIMAL_EXPORT template <typename DecimalType>
 constexpr auto from_chars(const char* first, const char* last, DecimalType& value, std::chars_format fmt) noexcept
@@ -147,6 +223,13 @@ constexpr auto from_chars(const char* first, const char* last, DecimalType& valu
 
     return std::from_chars_result {boost_r.ptr, boost_r.ec};
 }
+
+BOOST_DECIMAL_EXPORT template <typename DecimalType>
+constexpr auto from_chars(std::string_view str, DecimalType& value, std::chars_format fmt) noexcept
+    BOOST_DECIMAL_REQUIRES_RETURN(detail::is_decimal_floating_point_v, DecimalType, std::from_chars_result)
+{
+    return from_chars(str.data(), str.data() + str.size(), value, fmt);
+}
 #endif
 
 // ---------------------------------------------------------------------------------------------------------------------

include/boost/decimal/detail/config.hpp

@@ -323,6 +323,16 @@ typedef unsigned __int128 uint128_t;
 #      define BOOST_DECIMAL_HAS_STD_CHARCONV
 #    endif
 #  endif
+
+#  if __has_include(<string_view>)
+#    ifndef BOOST_DECIMAL_BUILD_MODULE
+#      include <string_view>
+#    endif
+#    if __cpp_lib_string_view >= 201606L
+#      define BOOST_DECIMAL_HAS_STD_STRING_VIEW
+#    endif
+#  endif
+
 #endif
 
 // Since we should not be able to pull these in from the STL in module mode define them ourselves

modules/decimal.cxx

@@ -30,6 +30,7 @@ module;
 #include <complex>
 #include <compare>
 #include <charconv>
+#include <string_view>
 
 // <stdfloat> is a C++23 feature that is not everywhere yet
 #if __has_include(<stdfloat>)

test/test_from_chars.cpp

@@ -162,6 +162,7 @@ void test_non_finite_values()
 
     const char* snan_str = "nan(snan)";
     auto r = from_chars(snan_str, snan_str + std::strlen(snan_str), val);
+    BOOST_TEST(r);
     BOOST_TEST(isnan(val));
 
     const char* qnan_str = "nan";
@@ -318,6 +319,17 @@ void test_from_chars_general_std()
 
 #endif
 
+template <typename T>
+void test_string_interface()
+{
+    constexpr T correct_val {42};
+    std::string str {"42"};
+    T val;
+    const auto r = from_chars(str, val);
+    BOOST_TEST(r);
+    BOOST_TEST_EQ(val, correct_val);
+}
+
 int main()
 {
     test_from_chars_scientific<decimal32>();
@@ -362,12 +374,25 @@ int main()
     test_hex_values<decimal32_fast>();
     test_hex_values<decimal64_fast>();
 
+    test_string_interface<decimal32>();
+    test_string_interface<decimal64>();
+    test_string_interface<decimal32_fast>();
+    test_string_interface<decimal64_fast>();
+
     #if !defined(BOOST_DECIMAL_REDUCE_TEST_DEPTH)
     test_from_chars_scientific<decimal128>();
     test_from_chars_fixed<decimal128>();
     test_from_chars_general<decimal128>();
     test_non_finite_values<decimal128>();
     test_hex_values<decimal128>();
+    test_string_interface<decimal128>();
+
+    test_from_chars_scientific<decimal128_fast>();
+    test_from_chars_fixed<decimal128_fast>();
+    test_from_chars_general<decimal128_fast>();
+    test_non_finite_values<decimal128_fast>();
+    test_hex_values<decimal128_fast>();
+    test_string_interface<decimal128_fast>();
     #endif
 
     return boost::report_errors();