4.6 sdds::FieldSelection, sdds::RowSlice, and sdds::ReadRequest

• name:
  sdds::FieldSelection, sdds::RowSlice, sdds::ReadRequest
• description:
  Select parameter, array, and column fields independently and select rows from each page. Projection is pushed into the decoder: unrequested fixed-width binary regions are skipped where possible and unrequested variable-width data is parsed and discarded. A page still retains the complete layout, but access to an unloaded field throws sdds::StateError.
• synopsis:
  static sdds::FieldSelection allFields();  
  static sdds::FieldSelection noFields();  
  static sdds::FieldSelection only(std::vector<std::string> names);  
   
  struct sdds::RowSlice {  
    std::int64_t first = 0;  
    std::optional<std::int64_t> count;  
    std::int64_t stride = 1;  
    std::optional<std::int64_t> last;  
  };  
   
  struct sdds::ReadRequest {  
    FieldSelection parameters, arrays, columns;  
    RowSlice rows;  
  };

• arguments:
  • names — Exact names to load for one field category.
  • first — First source row considered.
  • count — Optional maximum number of source rows considered.
  • stride — Positive source-row interval.
  • last — Optional trailing-row count, mutually exclusive with first and count selection.
• return value:
  The factory methods return a field selection. A default ReadRequest loads all fields and all rows.
• exceptions:
  sdds::StateError for an invalid slice or missing projected name, or sdds::LimitError when projected-field limits are exceeded.
• see also:
  Sections 4.13 and 4.7.