ReadNext statement [Revelation On-Line Wiki]

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====== ReadNext statement ======


==== Description ====
 
Extracts the next key from the list of keys, until the list is exhausted.
 
==== Syntax ====
 
**ReadNext** //variable// [ , //value//] [USING cursorvar] Then %%|%%  Else //statements//

The ReadNext statement has the following fcparameters.

^Parameter^Description^
|//variable//|Is assigned the row key from the selected list.|
|//value//|When a multi-valued sort list is being used, you can use the optional variable //value//. It returns the position of variable in the multi-valued field.|
|cursorvar|A variable containing the cursor variable set for this table in a  [[select_by|Select...By statement]].|
|Then|Executed if the ReadNext is successful|
|Else|The statement(s) following Else are executed if a key cannot be read from the selected list, for example, when the list has been exhausted. The [[status|Status()]] function indicates the reason for the false branch, and the system variable @FILE_ERROR contains details about the nature of the error.|


Note:  A ReadNext may return a null record key before the active list is exhausted. Testing for the null key is not a reliable test for list exhaustion.


Use ReadNext to read the keys from a selected list. The list of keys can be from a BASIC+ Select statement. A Select statement is used in the BASIC+ program to create a list of record keys. For more information, refer to Read. 

{{{guides:programming:programmers_reference_manual:caution.gif?28x21}} **Caution:** If you exit a ReadNext loop before exhausting the select list, you must clear the select list using [[clearselect|ClearSelect]]. Otherwise, your results may be unpredictable.


==== Examples ====

Processing the CUSTOMERS table.

<code>
declare function Set_FSError

open "CUSTOMERS" To customers_table else

 status = Set_FSError()

 return

end

select customers_table

Done = 0

loop

ReadNext @ID else Done = 1

Until Done Do

read @RECORD From customers_table, @ID else

status = Set_FSError()

return

end

* processing logic here ...

GoSub PROCESS

Repeat

return 0

PROCESS:

   /* process the row */

return

return
</code>

==== See Also ====
 
[[read|Read]], [[select|Select]]