How to unbind the definition by OCIDefineByPos?

I precomiled a query SQL when the program initialized. For example , the SQL has 10 columns, and I used OciDefineByPos to define the column ouput.I want to define 5 column In function A and define the other column in function B.

In ODBC,before define the other cols in function B,I must call SQLFreeStmt(hstmt,SQL_UNBIND) .

I want to know, with OCI,in function B, how to unbind the definitions which were defined in function A.

thanks!