Problem fetching multiple values in a TIMESTAMP column

Question

Hi all,
I'm having a problem trying to fetch multiple values in a TIMESTAMP column. I can successfully fetch the TIMESTAMP column if I do the following:
OCIDateTime tstmpltz = (OCIDateTime )NULL;
rc = OCIDescriptorAlloc(p_env,(dvoid **)&tstmpltz, OCI_DTYPE_TIMESTAMP,
0, (dvoid **)0);
rc = OCIDefineByPos(p_sql, &p_dfn, p_err, 1, &tstmpltz, sizeof(tstmpltz),
SQLT_TIMESTAMP, 0, 0, 0, OCI_DEFAULT);
This works fine. I can then do what I want with the OCIDateTime variable tstmpltz, like convert it to a text string, etc.
But what I am trying to do is fetch many rows of data that could include a TIMESTAMP column. For character columns this is no problem. I simply allocate a buffer of the correct width and length and then do my OCIDefineByPos to point to the start and the character data gets filled in. Same for numeric columns as well.
I can do this with a TIMESTAMP column if I do the OCIDefineByPos with a column type of SQLT_CHR. But the problem I'm running into when I do things this way is if I fetch a Timestamp value that is before 1950 I believe it is, I get back the wrong century. So for instance 1900 comes back as 2000. I think this is because the default date format when fetching is a 2 digit year. So I've tried to the do following:
long fetchrows = 50;
unsigned char *descpp1;
descpp1 = (unsigned char *)calloc(fetchrows, sizeof (OCIDateTime *));
int i;
for (i = 0; i != fetchrows; i++)
/* Allocate descriptors */
rc = OCIDescriptorAlloc((void *)p_env,(void **)&descpp1[i * sizeof (OCIDateTime *)], OCI_DTYPE_TIMESTAMP,
0,(void **)0);
// Bind the column
rc = OCIDefineByPos(p_sql, &p_dfn, p_err, 1, descpp1, sizeof(descpp1),
SQLT_TIMESTAMP, 0, 0, 0, OCI_DEFAULT);
rc = OCIStmtExecute(p_svc, p_sql, p_err, (ub4) 50, (ub4) 0,
(CONST OCISnapshot *) NULL, (OCISnapshot *) NULL,
OCI_DEFAULT);
And I get an "ORA-01403: no data found" error. I'm missing something here but I can't figure out what it is. Is this proper way to fetch multiple Timestamp columns ?
Thanks,
Nick

Answer 1

Hi Nick,
I think the "trick" here is that when you call OCIDescriptorAlloc normally you would pass a pointer to an OCIDateTime pointer (i.e. OCIDateTime**). However, you're being sneaky here and using unsigned char * with malloc/calloc for the reasons you have already mentioned. So, that changes things a bit because in this scenario the "destination address" where OCI is going to put the address for the OCIDateTime descriptor is in the memory you have dynamically allocated rather than in the target pointer of an OCIDateTime** declaration. So far so good, but the problem, as you've discovered, comes about when you need to get the OCIDateTime* to pass into the OCIDateTimeToText function. In your call you have this:
(OCIDateTime *)descpp1[0 * sizeof (OCIDateTime *)]However, that isn't the address of the descriptor it's a pointer to the address so, depending on your actual calls, etc. you'll either get a memory violation or an invalid OCI handle error. What you can do is get the address from that memory location and stuff it into a proper OCIDateTime* and then it can be used in the OCIDateTimeToText function.
I'm probably doing a terrible job explaining it, but I have cobbled together a sample which does what you want (at least as far as I can tell). Of course, being OCI, there's a fair bit of code, but here's the main parts.
I created a table called "ts_test" that has the following structure and sample data:
SQL> desc ts_test
Name             Null?    Type
TS_ID                     NUMBER
TS_VALUE                  TIMESTAMP(3)
SQL> select * from ts_test order by ts_id;
     TS_ID TS_VALUE
         1 01-JAN-09 08.00.00.123 AM
         2 01-JAN-09 12.34.56.789 PM
         3 01-JAN-09 04.46.00.046 PM
         4 01-JAN-09 10.00.00.314 PM
4 rows selected.I use the same query as above in the OCI sample code to get the values back out of the table.
  ** will hold pointers to TimeStamp Descriptor memory
  unsigned char *pTSD = (unsigned char *) NULL;
  ** temp pointer used with descriptors
  OCIDateTime *pTemp = NULL;
  ** allocate memory for the ts_id column
  if ((pID_val = (ub4 *) malloc(sizeof(ub4) * arrsize)) == NULL)
    printf("Failed to allocate memory for pID_val!\n");
    return;
  ** allocate memory for the ts descriptors
  if ((pTSD = (unsigned char *) malloc(sizeof(unsigned char *) * arrsize)) == NULL)
    printf("Failed to allocate memory for pTSD!\n");
    return;
  ** allocate date time descriptors
  for (i = 0; i < arrsize; i++)
    rc = OCIDescriptorAlloc(pDBCtx->envhp,
                            (void **) &pTSD[i * sizeof(OCIDateTime *)],
                            (ub4) OCI_DTYPE_TIMESTAMP,
                            (size_t) 0,
                            (void **) 0);
  ** define the first column in the results
  rc = OCIDefineByPos(stmtp,
                      &defnp,
                      pDBCtx->errhp,
                      (ub4) 1,
                      (void *) pID_val,
                      (sword) sizeof(ub4),
                      (ub2) SQLT_INT,
                      (void *) pID_ind,
                      (ub2 *) 0,
                      (ub2 *) 0,
                      (ub4) OCI_DEFAULT);
  ** define the second column in the results
  rc = OCIDefineByPos(stmtp,
                      &defnp,
                      pDBCtx->errhp,
                      (ub4) 2,
                      (void *) &pTSD[0],
                      (sword) sizeof(OCIDateTime *),
                      (ub2) SQLT_TIMESTAMP,
                      (void *) pTS_ind,
                      (ub2 *) 0,
                      (ub2 *) 0,
                      (ub4) OCI_DEFAULT);
  ** execute the statement
  rc = OCIStmtExecute(pDBCtx->svchp,
                      stmtp,
                      pDBCtx->errhp,
                      (ub4) arrsize,
                      (ub4) 0,
                      (CONST OCISnapshot *) NULL,
                      (OCISnapshot *) NULL,
                      (ub4) OCI_DEFAULT);
  ** get the text value of the timestamp
  ** null-terminate it, and display the value.
  ** the address of the allocated descriptor
  ** is copied from the dynamically allocated
  ** memory to the temp variable and that
  ** is passed to OCIDateTimeToText
  for (i = 0; i < arrsize; i++)
    memcpy((void *) &pTemp, &pTSD[i * sizeof(OCIDateTime *)], sizeof(OCIDateTime *));
    rc = OCIDateTimeToText((void *) pDBCtx->usrhp,
                           pDBCtx->errhp,
                           pTemp,
                           (oratext *) 0,
                           (ub1) 0,
                           (ub1) 3,
                           (oratext *) 0,
                           (size_t) 0,
                           &buflen,
                           buf);
    buf[buflen] = '\0';
    printf("Timestamp value[%d]: %s\n", *pID_val++, buf);
...Obviously there's lots left out, but hopefully that can be of some help. I've not really thoroughly reviewed the code so there may be a few things to fix. Anyway, using the above table and data the full sample outputs this on my system:
Timestamp value[1]: 01-JAN-09 08.00.00.123 AM
Timestamp value[2]: 01-JAN-09 12.34.56.789 PM
Timestamp value[3]: 01-JAN-09 04.46.00.046 PM
Timestamp value[4]: 01-JAN-09 10.00.00.314 PM
ENTER to continue...Thanks,
Mark