====== ReadO statement   ======

 


 
==== Description ====
 
Use to read a record that you do not intend to modify.
 
==== Syntax ====
 
**ReadO** //variable// From [//table_var//  Cursor //cursorvar//], //key// Then %%|%%  Else //statements//
 
==== Parameters ====
 
The ReadO statement has the following parameters.

^Parameter^Description^
|//variable//|Assigned the value of the data from the specified column of the row specified by //key//.|
|//Table_var//|A table variable that has been previously specified in an [[open|Open statement]].|
|cursorvar|If accessing a cursor, //cursorvar// contains a cursor variable. Cursor variables are initialized with a Select...By statement and must be preceded with the word Cursor.\\  \\ \\ If the table being accessed has had control features added, cursor access will automatically invoke domain conversion during a ReadO.|
|//Key//|The row referenced by //key// will be read from the table identified by //table_var// or the table accessed using the cursor in //cursorvar//.|
|Then|The statements in the Then clause will be executed if a row is read successfully.|
|Else|The statement(s) following Else are executed if the row in //variable// cannot be read. The [[status|Status() function]] indicates the severity of the error, and the system variable @FILE_ERROR contains details about the nature of the error.\\ ||

 
==== Note ====
 
ReadO is used to read a row that will not be updated.  As a consequence, the read request may be fulfilled from any cache or buffers being maintained by the filing system.  ReadO, therefore, can be a faster method of accessing data than by using the [[read|Read statement]].  In a multi-user environment, ReadO does not necessarily read the most current version of a row.

Note:  The definition of ReadO (and the use of caches or buffers) is specific to the filing system being used.  Many filing systems do not cache data and therefore implement [[read|Read]] and ReadO identically.
 
==== See Also ====
 
[[matread|MatRead]], [[open|Open]], [[read|Read]], [[write|Write]], [[xlate|Xlate()]]
 
==== Example ====
 
<code>
/*  This code fragment counts the number of bytes in the CUSTOMERS table.

The result is stored in data_bytes at the end of the loop.  ReadO is used because record locking is unnecessary, since the only purpose of reading each row is to determine its length.

*/

 

Open "CUSTOMERS" To customers_file Then

data_bytes = 0

Select customers_file

Done = 0

Loop

  ReadNext @id Else Done = 1

Until Done do

  ReadO @record From customers_file, @id Then

    data_bytes += len(@record) + len(@id)

  End

Repeat

/*  data_bytes contains the number of data bytes in the table. */

End
</code>