is OCIDefineArrayOfStruct() needed for each subsequent OCIDefineByPos() ?

Hello,
According to my application logic, I change the DEFINE addresses between each FETCH. do I have to call OCIDefineArrayOfStruct() after each OCIDefineByPos() ?

Here is the pseudo code:

OCIDefineByPos();
OCIDefineArrayOfStruct();

while (OCIStmtFetch2()==OCI_SUCCESS)
 {
.....
OCIDefineByPos();
.....
 }

as seen above, I call it just one time before the first FECTH and it works. But, I need a confirmation.

thanks in advance...