Function executeString

src/Functions/array/emptyArrayToSingle.cpp:169–257

        template <bool nullable>
        bool executeString(
            const IColumn & src_data, const ColumnArray::Offsets & src_array_offsets,
            IColumn & res_data_col, ColumnArray::Offsets & res_array_offsets,
            const NullMap * src_null_map,
            NullMap * res_null_map)
        {
            if (const ColumnString * src_data_concrete = checkAndGetColumn<ColumnString>(&src_data))
            {
                const ColumnString::Offsets & src_string_offsets = src_data_concrete->getOffsets();

                auto * concrete_res_string_offsets = typeid_cast<ColumnString *>(&res_data_col);
                if (!concrete_res_string_offsets)
                    throw Exception(ErrorCodes::LOGICAL_ERROR, "Internal error");
                ColumnString::Offsets & res_string_offsets = concrete_res_string_offsets->getOffsets();

                const ColumnString::Chars & src_data_vec = src_data_concrete->getChars();

                auto * concrete_res_data = typeid_cast<ColumnString *>(&res_data_col);
                if (!concrete_res_data)
                    throw Exception(ErrorCodes::LOGICAL_ERROR, "Internal error");
                ColumnString::Chars & res_data = concrete_res_data->getChars();

                size_t size = src_array_offsets.size();
                res_array_offsets.resize(size);
                res_string_offsets.reserve(src_string_offsets.size());
                res_data.reserve(src_data_vec.size());

                if (nullable)
                    res_null_map->reserve(src_null_map->size());

                ColumnArray::Offset src_array_prev_offset = 0;
                ColumnArray::Offset res_array_prev_offset = 0;

                ColumnString::Offset src_string_prev_offset = 0;
                ColumnString::Offset res_string_prev_offset = 0;

                for (size_t i = 0; i < size; ++i)
                {
                    if (src_array_offsets[i] != src_array_prev_offset)
                    {
                        size_t array_size = src_array_offsets[i] - src_array_prev_offset;

                        size_t bytes_to_copy = 0;
                        size_t from_string_prev_offset_local = src_string_prev_offset;
                        for (size_t j = 0; j < array_size; ++j)
                        {
                            size_t string_size = src_string_offsets[src_array_prev_offset + j] - from_string_prev_offset_local;

                            res_string_prev_offset += string_size;
                            res_string_offsets.push_back(res_string_prev_offset);

                            from_string_prev_offset_local += string_size;
                            bytes_to_copy += string_size;
                        }

                        size_t res_data_old_size = res_data.size();
                        res_data.resize(res_data_old_size + bytes_to_copy);
                        memcpy(&res_data[res_data_old_size], &src_data_vec[src_string_prev_offset], bytes_to_copy);