Fix iterator_input_adapter for types not supported by char_traits

include/nlohmann/detail/input/input_adapters.hpp

@@ -132,10 +132,70 @@ class input_stream_adapter
 };
 #endif // JSON_NO_IO
 
+template<typename T>
+struct has_char_traits : std::false_type {};
+
+template<>
+struct has_char_traits<char> : std::true_type {};
+
+template<>
+struct has_char_traits<wchar_t> : std::true_type {};
+
+#ifdef JSON_HAS_CPP_20
+template<>
+struct has_char_traits<char8_t> : std::true_type {};
+
+template<>
+struct has_char_traits<char16_t> : std::true_type {};
+
+template<>
+struct has_char_traits<char32_t> : std::true_type {};
+#endif
+
+template<typename T>
+struct is_iterator_of_char : has_char_traits<typename std::iterator_traits<T>::value_type> {};
+
 // General-purpose iterator-based adapter. It might not be as fast as
 // theoretically possible for some containers, but it is extremely versatile.
-template<typename IteratorType>
+template<typename IteratorType, typename Enable = void>
 class iterator_input_adapter
+{
+ public:
+ using char_type = char;
+ using value_type = typename std::iterator_traits<IteratorType>::value_type;
+
+ iterator_input_adapter(IteratorType first, IteratorType last)
+ : current(std::move(first)), end(std::move(last))
+ {}
+
+ typename std::char_traits<char>::int_type get_character()
+ {
+ if (JSON_HEDLEY_LIKELY(current != end))
+ {
+ // Cast to unsigned to avoid EOF and 0xFF having same value
+ auto result = static_cast<typename std::make_unsigned<value_type>::type>(*current);
+ std::advance(current, 1);
+ return static_cast<std::char_traits<char>::int_type>(result);
+ }
+
+ return std::char_traits<char>::eof();
+ }
+
+ private:
+ IteratorType current;
+ IteratorType end;
+
+ template<typename BaseInputAdapter, size_t T>
+ friend struct wide_string_input_helper;
+
+ bool empty() const
+ {
+ return current == end;
+ }
+};
+
+template<typename IteratorType>
+class iterator_input_adapter<IteratorType, enable_if_t<is_iterator_of_char<IteratorType>::value>>
 {
  public:
  using char_type = typename std::iterator_traits<IteratorType>::value_type;

single_include/nlohmann/json.hpp

@@ -6208,10 +6208,70 @@ class input_stream_adapter
 };
 #endif // JSON_NO_IO
 
+template<typename T>
+struct has_char_traits : std::false_type {};
+
+template<>
+struct has_char_traits<char> : std::true_type {};
+
+template<>
+struct has_char_traits<wchar_t> : std::true_type {};
+
+#ifdef JSON_HAS_CPP_20
+template<>
+struct has_char_traits<char8_t> : std::true_type {};
+
+template<>
+struct has_char_traits<char16_t> : std::true_type {};
+
+template<>
+struct has_char_traits<char32_t> : std::true_type {};
+#endif
+
+template<typename T>
+struct is_iterator_of_char : has_char_traits<typename std::iterator_traits<T>::value_type> {};
+
 // General-purpose iterator-based adapter. It might not be as fast as
 // theoretically possible for some containers, but it is extremely versatile.
-template<typename IteratorType>
+template<typename IteratorType, typename Enable = void>
 class iterator_input_adapter
+{
+ public:
+ using char_type = char;
+ using value_type = typename std::iterator_traits<IteratorType>::value_type;
+
+ iterator_input_adapter(IteratorType first, IteratorType last)
+ : current(std::move(first)), end(std::move(last))
+ {}
+
+ typename std::char_traits<char>::int_type get_character()
+ {
+ if (JSON_HEDLEY_LIKELY(current != end))
+ {
+ // Cast to unsigned to avoid EOF and 0xFF having same value
+ auto result = static_cast<typename std::make_unsigned<value_type>::type>(*current);
+ std::advance(current, 1);
+ return static_cast<std::char_traits<char>::int_type>(result);
+ }
+
+ return std::char_traits<char>::eof();
+ }
+
+ private:
+ IteratorType current;
+ IteratorType end;
+
+ template<typename BaseInputAdapter, size_t T>
+ friend struct wide_string_input_helper;
+
+ bool empty() const
+ {
+ return current == end;
+ }
+};
+
+template<typename IteratorType>
+class iterator_input_adapter<IteratorType, enable_if_t<is_iterator_of_char<IteratorType>::value>>
 {
  public:
  using char_type = typename std::iterator_traits<IteratorType>::value_type;