#include <sqludf.h>
extern int SQL_API_FN sqludf_substr(
udf_locator * udfloc_p,
long start,
long length,
unsigned char * buffer_p,
long * return_len_p)
Service Program Name: QSYS/QSQAPISThe sqludf_substr() function returns a substring of the LOB data the locator represents.
No authorization is required.
returns an integer. Possible values are:
| Message ID | Error Message Text |
|---|---|
| SQL7034 D | LOB locators are not allowed with COMMIT(*NONE). |
| SQL0901 D | SQL system error. |
| SQL0952 D | Processing of the SQL statement ended. |
| CPF9872 E | Program or service program &1 in library &2 ended. Reason code &3. |
See Code disclaimer information for information pertaining to code examples.
This UDF takes a locator for an input LOB, and returns a locator for another LOB which is a subset of the input LOB. There are some criteria passed as a second input value, which tell the UDF how exactly to break up the input LOB.
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <sql.h>
#include <sqludf.h>
void SQL_API_FN lob_subsetter(
udf_locator * lob_input, /* locator of LOB value to carve up */
char * criteria, /* criteria for carving */
udf_locator * lob_output, /* locator of result LOB value */
sqlint16 * inp_nul,
sqlint16 * cri_nul,
sqlint16 * out_nul,
char * sqlstate,
char * funcname,
char * specname,
char * msgtext ) {
/* local vars */
short j; /* local indexing var */
int rc; /* return code variable for API calls */
sqlint32 input_len; /* receiver for input LOB length */
sqlint32 input_pos; /* current position for scanning input LOB */
char lob_buf[100]; /* data buffer */
sqlint32 input_rec; /* number of bytes read by sqludf_substr */
sqlint32 output_rec; /* number of bytes written by sqludf_append */
/*---------------------------------------------
* UDF Program Logic Starts Here
*---------------------------------------------
* What we do is create an output handle, and then
* loop over the input, 50 bytes at a time.
* Depending on the "criteria" passed in, we may decide
* to append the 50 byte input lob segment to the output, or not.
*---------------------------------------------
* Create the output locator, right in the return buffer.
*/
rc = sqludf_create_locator(SQL_TYP_CLOB, &lob_output);
/* Error and exit if unable to create locator */
if (rc) {
memcpy (sqlstate, "38901", 5);
/* special sqlstate for this condition */
goto exit;
}
/* Find out the size of the input LOB value */
rc = sqludf_length(lob_input, &input_len) ;
/* Error and exit if unable to find out length */
if (rc) {
memcpy (sqlstate, "38902", 5);
/* special sqlstate for this condition */
goto exit;
}
/* Loop to read next 50 bytes, and append to result if it meets
* the criteria.
*/
for (input_pos = 1; (input_pos < input_len); input_pos += 50) {
/* Read the next 50 (or less) bytes of the input LOB value */
rc = sqludf_substr(lob_input, input_pos, 50,
(unsigned char *) lob_buf, &input_rec) ;
/* Error and exit if unable to read the segment */
if (rc) {
memcpy (sqlstate, "38903", 5);
/* special sqlstate for this condition */
goto exit;
}
/* apply the criteria for appending this segment to result
* if (...predicate involving buffer and criteria...) {
* The example shows if the segment matches the first 6
* characters with the criteria it is appended.
*/
if (memcmp(lob_buf,criteria,6) == 0) {
rc = sqludf_append(lob_output,
(unsigned char *) lob_buf, input_rec, &output_rec) ;
/* Error and exit if unable to read the 50 byte segment */
if (rc) {
memcpy (sqlstate, "38904", 5);
/* special sqlstate for this condition */
goto exit;
}
}
/* } end if criteria for inclusion met */
} /* end of for loop, processing 50-byte chunks of input LOB
* if we fall out of for loop, we are successful, and done.
*/
*out_nul = 0;
exit: /* used for errors, which will override null-ness of output. */
return;
}
Referring to this UDF code, observe that:
Following is the CREATE FUNCTION statement for this UDF:
CREATE FUNCTION carve(CLOB(50M) AS LOCATOR, VARCHAR(255) )
RETURNS CLOB(50M) AS LOCATOR
NOT NULL CALL
DETERMINISTIC
NO SQL
NO EXTERNAL ACTION
LANGUAGE C
PARAMETER STYLE DB2SQL
EXTERNAL NAME 'MYLIB/LOBUDFS(lob_subsetter)' ;
Referring to this statement, observe that:
Now you can successfully run the following statement:
strcpy(hvchar,"return this text 1 "
"remove 1 "
"return this text 2 "
"remove 2 ");
exec sql set :hvloc = clob(:hvchar);
exec sql set :hvloc2 = carve(:hvloc,'return');
strcpy(hvchar,"");
exec sql set :hvchar = char(:hvloc2);
The UDF is used to subset the value represented by the host variable :hvchar. The first and third 50 byte character segments are returned from the UDF.
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