isc_blob_default_desc2()

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Loads a data structure with default information about a Blob, including its subtype, character set, and segment size. For more information about Blob descriptors, see Working with Blob Data.

Syntax

void isc_blob_default_desc2(
ISC_BLOB_DESC_V2 *desc,
unsigned char *table_name,
unsigned char *column_name);

Parameter Type Description

desc

ISC_BLOB_DESC_V2 *

Pointer to a Blob descriptor

table_name

unsigned char *

Table name

column_name

unsigned char *

Blob column name

Description

isc_blob_default_desc2() loads a Blob descriptor, desc, with the specified ­table_name and column_name, and the following default values prior to calling isc_blob_gen_bpb2() to generate a Blob parameter buffer (BPB) for the Blob column being accessed:

  • Subtype is set to TEXT.
  • Character set is set to the default character set for the process or ­database.
  • Segment size is set to 80 bytes.
  • ISC_BLOB_DESC_V2 supports long metadata names of length METADATALENGTH. The older ISC_BLOB_DESC structure supports only metadata names of 32 bytes or less.

isc_blob_default_desc2() and three related functions, isc_blob_gen_bpb2(), isc_blob_lookup_desc2(), and isc_blob_set_desc2(), provide dynamic access to Blob information. In particular, these functions can define and access information about a Blob for filtering purposes, such as character set information for text Blob data, and subtype information for text and non-text Blob data.

The following table lists the fields in the desc structure:

Blob descriptor fields
Parameter Type Description

blob_desc_version

short

Set to BLOB_DESC_CURRENT_VERSION

blob_desc_subtype

short

Subtype of the Blob filter

blob_desc_charset

short

Character set being used

blob_desc_segment_size

short

Blob segment size

blob_desc_field_name [METADATALENGTH]

char

Array containing the name of the Blob column

blob_desc_relation_name [METADATALENGTH]

char

Array containing the name of the table in which the Blob is stored

Example

The following fragment loads the Blob descriptor with default information:

typedef struct {
short blob_desc_version
short blob_desc_subtype;
short blob_desc_charset;
short blob_desc_segment_size;
unsigned char blob_desc_field_name[METADATALENGTH];
unsigned char blob_desc_relation_name[METADATALENGTH];
} ISC_BLOB_DESC2;
isc_blob_default_desc2(&desc, &relation, &field);

Return value

None.

See Also

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