====== Simple (Latent) Select ======

In BASIC+, a simple [[select|SELECT statement]]  (not an extended [[select_by|SELECT ... BY statement]]) does not directly produce a list of record keys for processing. Instead, the [[select_|SELECT statement]] simply initializes variables in the system, indicating that a select condition is active.

In addition, the SELECT is passed to the filing system so it can perform any filing system-specific activity to initialize a select condition.  A filing system SELECT call returns a select mode with three possible values in the RECORD argument:

^Select Mode^Meaning^
|0|No select list is active (disable the select)|
|1|Latent file select|
|2|Latent index select|

 

If a select condition is active, subsequent BASIC+ [[readnext|READNEXT statements]] will return record keys until the file has been exhausted. If no select list is active, a subsequent BASIC+ [[readnext|READNEXT statement]] will fall through its ELSE branch.

The select mode value is available to a BASIC+ program in the system variable [[cursors_and_select_lists|@LIST.ACTIVE]].  If the SELECT call fails for any reason, the RECORD argument is passed back false, indicating to the system that no select list is active.  [[cursors_and_select_lists|@LIST.ACTIVE]] will also be set to false.

This BASIC+ program fragment illustrates the typical flow of a simple SELECT:

<code>
SELECT FILE ; * establish "latent" select
DONE = 0
LOOP
  READNEXT @ID ELSE DONE = 1
  UNTIL DONE DO
    /* process the row */
REPEAT
</code>