executing procedure with CLOB parameter from C

Hi,

i'm trying to execute PL/SQL procedure from C using OCI. database: oracleDB 9.2

That procedure has one parameter, CLOB,
and the question is, how to transfer that CLOB to procedure.

I have the following piece of code (assuming that handles are initialized):

--------cut

 char select[] = "select MY_PACK.load_xml( :xml ) from dual"; char my_txt[] ="testing testing";

   rc = OCIStmtPrepare(p_sql, p_err, (OraText*)select,

(ub4) strlen( select ), (ub4) OCI_NTV_SYNTAX, (ub4) OCI_DEFAULT);
   if( checkerr( p_err, rc ) != 0 )

                   return 1;

  rc = OCIBindByName(p_sql, &p_bnd, p_err, (text *) ":xml", 4,

   		   (dvoid **) my_txt, strlen(my_txt) , SQLT_CHR, (dvoid *) 0,


           (ub2 *) 0, (ub2 *) 0, (ub4) 0, (ub4 *) 0, OCI_DEFAULT);

    if( checkerr( p_err, rc ) != 0 )
	   	return 1;

	rc = OCIDefineByPos(p_sql, &p_dfn, p_err, 1, (dvoid *) &p_int,


           (sword) 4, SQLT_INT, (dvoid *) 0, (ub2 *)0,

           (ub2 *)0, OCI_DEFAULT);

   if( checkerr( p_err, rc ) != 0 )
	   	return 1;
         
rc = OCIStmtExecute(p_svc, p_sql, p_err, (ub4) 1, (ub4) 0,


           (CONST OCISnapshot *) NULL, (OCISnapshot *) NULL, OCI_DEFAULT);

    if( checkerr( p_err, rc ) != 0 )
 	   	return 1;

--------cut

in this way, my string is insterted, (conversion STR->CLOB occurs), but for data larger that about 2k there is an error:  ORA-01460: unimplemented or unreasonable conversion requested ok, that fine, i should use CLOB's from the beginning, but how to do that?
how to use OCILOBLocator in 'select' clause ? Do you have any idea? or pieco of example code ?

-- 
best regards,
lukes