Generating a Blob Parameter Buffer Using API Calls

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To generate a BPB indirectly, use API calls to create source and target Blob descriptors, and then call isc_blob_gen_bpb2() to generate the BPB from the information in the descriptors. Follow these steps:

Declare two Blob descriptors, one for the source, and the other for the target. For example,
```
#include <ibase.h>
ISC_BLOB_DESC_V2 from_desc, to_desc;
```

Store appropriate information in the Blob descriptors, by calling one of the functions isc_blob_default_desc2(), isc_blob_lookup_desc2(), or isc_blob_set_desc2(), or by setting the descriptor fields directly. The following example looks up the current subtype and character set information for a Blob column named GUIDEBOOK in a table named TOURISM, and stores it into the source descriptor, from_desc. It then sets the target descriptor, to_desc to the default subtype (TEXT) and character set, so that the source data will be converted to plain text.

isc_blob_lookup_desc2 ( status_vector,
&db_handle; /* set in previous isc_attach_database() call */
&tr_handle, /* set in previous isc_start_transaction() call */
"TOURISM", /* table name */
"GUIDEBOOK", /* column name */
&from_desc, /* Blob descriptor filled in by this function call */
&global);
if (status_vector[0] == 1 && status_vector[1]) {
/* process error */
isc_print_status(status_vector);
return(1);
};
isc_blob_default_desc2 (
&to_desc, /* Blob descriptor filled in by this function call */
"", /* NULL table name; it's not needed in this case */
""); /* NULL column name; it's not needed in this case */

For more information about Blob descriptors, see Filtering Blob Data.

Declare a character array which will be used as the BPB. Make sure it is at least as large as all the information that will be stored in the buffer.
```
char bpb[20];
```
Declare an unsigned short variable into which InterBase will store the actual length of the BPB data:
```
unsigned short actual_bpb_length;
```

Call isc_blob_gen_bpb2() to populate the BPB based on the source and target Blob descriptors passed to isc_blob_gen_bpb2(). For example,

isc_blob_gen_bpb2(status_vector,
&to_desc, /* target Blob descriptor */
&from_desc, /* source Blob descriptor */
sizeof(bpb), /* length of BPB buffer */
bpb, /* buffer into which the generated BPB will be stored */
&actual_bpb_length); /* actual length of generated BPB */

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Generating a Blob Parameter Buffer Directly