Guyub – Konsultan F/OSS

Each column is stored in a type-specific way.
Each Table (an instance of an open table which a Cursor is used to iterate over parts of) has two row buffers in it: record[0] and record[1]. For the most part, the Cursor implementation for your Storage Engine only ever has to deal with record[0]. However, sometimes you may be asked to read a row into record[1], so your engine must deal with that too.
A Row (no, there#8217;s no object for that#8230; you just get a pointer to somewhere in memory) is made up of Fields (as in Field objects). It#8217;s really made up of lots of things, but if you#8217;re dealing with the row format, a row is made up of fields. The Field objects let you get the value out of a row in a number of ways. For an integer column, you can call Field::val_int() to get the value as an integer, or you can call val_str() to get it as a string (this is what the CSV engine does, just calls val_str() on each Field).
The Field objects are not part of a row in any way. They instead have a pointer to record[0] stored in them. This doesn#8217;t help you if you need to access record[1] (because that can be passed into your Cursor methods). Although the buffer passed into various Cursor methods is usually record[0] it is not always record[0]. How do you use the Field objects to access fields in the row buffer then? The answer is the Field::move_field_offset(ptrdiff_t) method. Here is how you can use it in your code:

ptrdiff_t row_offset= buf – table-gt;record[0];
(**field).move_field_offset(row_offset);
(do things with field)
(**field).move_field_offset(-row_offset);