LASS="FUNCTION"
>PQinstanceData</CODE
>,
   <CODE
CLASS="FUNCTION"
>PQsetInstanceData</CODE
>,
   <CODE
CLASS="FUNCTION"
>PQresultInstanceData</CODE
> and
   <CODE
CLASS="FUNCTION"
>PQsetResultInstanceData</CODE
> functions.  Note that
   unlike the passthrough pointer, instance data of a <TT
CLASS="STRUCTNAME"
>PGconn</TT
>
   is not automatically inherited by <TT
CLASS="STRUCTNAME"
>PGresult</TT
>s created from
   it.  <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> does not know what passthrough
   and instance