fix: std::istream autodetect delimeter (#272)

include/internal/basic_csv_parser.hpp

@@ -83,6 +83,16 @@ namespace csv {
 
         CSV_INLINE std::string get_csv_head(csv::string_view filename);
 
+        template<typename TStream,
+            csv::enable_if_t<std::is_base_of<std::istream, TStream>::value, int>  = 0>
+        std::string get_csv_head(TStream &source) {
+            auto tellg = source.tellg();
+            std::string head;
+            std::getline(source, head);
+            source.seekg(tellg);
+            return head;
+        }
+
         /** Read the first 500KB of a CSV file */
         CSV_INLINE std::string get_csv_head(csv::string_view filename, size_t file_size);
 

include/internal/csv_reader.hpp

@@ -117,9 +117,17 @@ namespace csv {
          */
         template<typename TStream,
             csv::enable_if_t<std::is_base_of<std::istream, TStream>::value, int> = 0>
-        CSVReader(TStream& source, CSVFormat format = CSVFormat()) : _format(format) {
+        CSVReader(TStream &source, CSVFormat format = CSVFormat::guess_csv()) : _format(format) {
+            auto head = internals::get_csv_head(source);
             using Parser = internals::StreamParser<TStream>;
 
+            if (format.guess_delim()) {
+                auto guess_result = internals::_guess_format(head, format.possible_delimiters);
+                format.delimiter(guess_result.delim);
+                format.header = guess_result.header_row;
+                this->_format = format;
+            }
+
             if (!format.col_names.empty())
                 this->set_col_names(format.col_names);