Reading and Processing the Blob Data

Go Up to Reading Data from a Blob

To read and process the Blob data:

1. Declare and initialize a Blob handle:

   isc_blob_handle blob_handle; /* Declare a Blob handle. */
   blob_handle = NULL; /* Set handle to NULL before using it */
   

2. Create a buffer for holding each Blob segment as it is read. Its size should be the maximum size segment your program expects to be read from the Blob.

   char blob_segment[80];
   

3. Declare an unsigned short variable into which InterBase will store the actual length of each segment read:

   unsigned short actual_seg_len;
   

4. Open the Blob with the fetched blob_id:

   isc_open_blob2( status_vector, &db_handle, &trans,
   &blob_handle, /* set by this function to refer to the Blob */
   &blob_id, /* Blob ID put into out_sqlda by isc_dsql_fetch() */
   0, /* BPB length = 0; no filter will be used */
   NULL ); /* NULL BPB, since no filter will be used */
   

5. Read all the Blob data by calling isc_get_segment() repeatedly to get each Blob segment and its length. Process each segment read. In the following example, “processing” consists of printing each Blob as it is read:

   blob_stat = isc_get_segment( status_vector,
   &blob_handle, /* set by isc_open_blob2()*/
   &actual_seg_len, /* length of segment read */
   sizeof(blob_segment), /* length of segment buffer */
   blob_segment ); /* segment buffer */
   while (blob_stat == 0 || status_vector[1] == isc_segment) {
   /* isc_get_segment returns 0 if a segment was successfully read. */
    * status_vector[1] is set to isc_segment if only part of a */
    * segment was read due to the buffer (blob_segment) not being */
    * large enough. In that case, the following calls to */
    * isc_get_segment() read the rest of the buffer. */
   printf("%*.*s", actual_seg_len, actual_seg_len, blob_segment);
   blob_stat = isc_get_segment(status_vector, &blob_handle,
   &actual_seg_len, sizeof(blob_segment), blob_segment);
   printf("\n");
   };
   printf("\n");
   

6. Close the Blob:

   isc_close_blob(status_vector, &blob_handle);
   

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