Populating a Blob Descriptor
Go Up to Working with Blob Data
There are four possible ways to populate a Blob descriptor, as follows:
isc_blob_default_desc2(). This stores default values into the descriptor fields. The default subtype is 1 (
TEXT), segment size is 80 bytes, and charset is the default charset for your process.
isc_blob_lookup_desc2(). This accesses the database system metadata tables to look up and copy information for the specified Blob column into the descriptor fields.
isc_blob_set_desc2(). This initializes the descriptor from parameters you call it with, rather than accessing the database metadata.
- Set the descriptor fields directly.
The following example calls
isc_blob_lookup_desc2() to look up the current subtype and character set information for a Blob column named
PROJ_DESC in a table named
PROJECT. It stores the information into the source descriptor,
isc_blob_lookup_desc2 ( status_vector, &db_handle; /* Set by previous isc_attach_database() call. */ &tr_handle, /* Set by previous isc_start_transaction() call. */ "PROJECT", /* Table name. */ "PROJ_DESC", /* Column name. */ &from_desc, /* Blob descriptor filled in by this function call. */ &global ) /* Global column name, returned by this function. */
For more information about the usage of Blob descriptors in applications that request data filtering, and for further examples of populating Blob descriptors, see Writing an Application that Requests Filtering.