Client-Library’s CS_IODESC structure

The CS_IODESC structure describes text or image data.

When retrieving text or image data from a column that will be updated, a Client-Library application calls ct_data_info to get the CS_IODESC structure that describes the text or image column.

Generally an application must call ct_get_data for the column before calling ct_data_info. However, when ct_get_data is used with Server-Library API srv_send_data, to transfer text, image, and XML columns in chunks in Gateway Open Server applications, call ct_data_info before calling ct_get_data.

If you do not need to retrieve the column’s data, assign 0 to buflen in ct_get_data. This technique is useful for determining the length of a text or image value before retrieving it.

For more information, see the Open Server Server-Library/C Reference Manual.

When updating the column, the application calls ct_data_info again to apply the CS_IODESC fields for the update operation.

DB-Library has specialized routines for manipulating the text timestamp for a column or value. In Client-Library, applications handle these tasks by calling ct_data_info and then modifying the resulting CS_IODESC structure directly.

A typical application only modifies three fields of a CS_IODESC structure before using it in an update operation:

• total_txtlen

  This field specifies the total length, in bytes, of the new value. This is equivalent to the size parameter to dbwritetext.

• log_on_update

  This field indicates whether or not the server should log the update. This is equivalent to the log parameter to dbwritetext.

• locale

  This field points to a CS_LOCALE structure containing localization information for the value, if any. It has no equivalent in DB-Library.

The timestamp field in CS_IODESC marks the time of a text or image column’s last modification.