added more documentation to from_chars and to_chars

dune/common/std/charconv.hh

@@ -71,6 +71,28 @@ namespace Dune
 
     namespace Impl
     {
+      /**
+       * \brief Performs the conversion of a character sequence [first, last) to
+       * a value of type `T` by using a `std::istringstream` formatted stream extracter.
+       * with format flags set by the `manipulator`.
+       *
+       * On success, returns a value of type \ref from_chars_result such that `ptr`
+       * points has the value equal to `last` if all characters match and `ec` is
+       * value-initialized.
+       *
+       * If there is no pattern match, returns a value of type \ref from_chars_result
+       * such that `ptr` equals `first` and `ec` equals `std::errc::invalid_argument`.
+       * `value` is unmodified.
+       *
+       * If the pattern was matched, but the parsed value is not in the range representable
+       * by the type of `value`, returns value of type \ref from_chars_result such
+       * that `ec` equals ´std::errc::result_out_of_range` and `ptr` points at the
+       * value equal to `last`. `value` is unmodified.
+       *
+       * NOTE: Can not determine pointer to the first character not matching the
+       *       pattern, as required by `std::for_each`. Returning `last` if all
+       *       characters are consumed.
+       **/
       template<typename T, typename StreamManipulator>
       from_chars_result fromCharsImpl (const char* first, const char* last, T& value,
                                        StreamManipulator manipulator)
@@ -95,11 +117,23 @@ namespace Dune
             return from_chars_result{first, std::errc::invalid_argument};
         }
 
-        // NOTE: Can not determine pointer to the first character not matching the pattern.
-        //       Returning last if all characters are consumed.
         return from_chars_result{s.eof() ? last : first, std::errc{}};
       }
 
+      /**
+       * \brief Performas a conversion of `value` of type `T` to a character
+       * sequence stored in the memory range [first, last) by using a
+       * `std::ostringstream` formatted stream inserter with format flags set by
+       * the `manipulator`.
+       *
+       * On success, returns a value of type \ref to_chars_result such that `ec`
+       * equals value-initialized `std::errc` and `ptr` is the one-past-the-end
+       * pointer of the characters written. Note that the string is not NUL-terminated.
+       *
+       * On error, returns a value of type \ref to_chars_result holding
+       * `std::errc::value_too_large` in `ec`, a copy of the value `last` in `ptr`,
+       * and leaves the contents of the range [first, last) in unspecified state.
+       **/
       template<typename T, typename StreamManipulator>
       to_chars_result toCharsImpl (char* first, char* last, T value,
                                    StreamManipulator manipulator)