The same as fill_sqlda, except that it changes all the data types in sqlda to type DT_STRING. Enough space is allocated to hold the string representation of the type originally specified by the SQLDA,
up to a maximum of maxlen bytes. The length fields in the SQLDA (sqllen) are modified appropriately. Returns sqlda if successful and returns the null pointer if there is not enough memory available.
The SQLDA should be freed using the free_filled_sqlda function.