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.

The application must call ct_get_data for the column before calling ct_data_info. If you do not need to retrieve the column’s data, you can code the ct_get_data call with a buflen of 0. This technique is useful for determining the length of a text or image value before retrieving it.

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.

The following table compares text timestamp functionality in DB-Library and Client-Library:

**Table 6-5: DB-Library vs. Client-Library—text timestamps**
DB-Library routines	DB-Library functionality	Client-Library equivalent
dbtxtimestamp( dbproc, column)	Return the value of the text timestamp for a column in the current row	Retrieve the I/O descriptor for a column in the current row and put it into CS_IODESC: ct_data_info( cmd, CS_GET, colnum, iodesc). The text timestamp is in `CS_IODESC` → `timestamp.`
dbtxptr( dbproc, column)	Return the value of the text pointer for a column in the current row	The text pointer is in `CS_IODESC` → `textptr`.
dbtxtsnewval( dbproc)	Return the new value of a text timestamp after a call to dbwritetext	Process the return parameter result set (ct_results returns with result_type of CS_PARAM_RESULT), which contains the new text timestamp value after a call to ct_send_data.