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>Chapter 31. <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> - C Library</TD
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><A
NAME="LIBPQ-FASTPATH"
>31.7. The Fast-Path Interface</A
></H1
><P
>   <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> provides a fast-path interface
   to send simple function calls to the server.
  </P
><DIV
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><P
><B
>Tip: </B
>    This interface is somewhat obsolete, as one can achieve similar
    performance and greater functionality by setting up a prepared
    statement to define the function call.  Then, executing the statement
    with binary transmission of parameters and results substitutes for a
    fast-path function call.
   </P
></BLOCKQUOTE
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><P
>   The function <CODE
CLASS="FUNCTION"
>PQfn</CODE
>
   requests execution of a server function via the fast-path interface:
</P><PRE
CLASS="SYNOPSIS"
>PGresult *PQfn(PGconn *conn,
               int fnid,
               int *result_buf,
               int *result_len,
               int result_is_int,
               const PQArgBlock *args,
               int nargs);

typedef struct
{
    int len;
    int isint;
    union
    {
        int *ptr;
        int integer;
    } u;
} PQArgBlock;</PRE
><P>
  </P
><P
>   The <TT
CLASS="PARAMETER"
>fnid</TT
> argument is the OID of the function to be
   executed.  <TT
CLASS="PARAMETER"
>args</TT
> and <TT
CLASS="PARAMETER"
>nargs</TT
> define the
   parameters to be passed to the function; they must match the declared
   function argument list.  When the <TT
CLASS="PARAMETER"
>isint</TT
> field of a
   parameter structure is true, the <TT
CLASS="PARAMETER"
>u.integer</TT
> value is sent
   to the server as an integer of the indicated length (this must be
   2 or 4 bytes); proper byte-swapping occurs.  When <TT
CLASS="PARAMETER"
>isint</TT
>
   is false, the indicated number of bytes at <TT
CLASS="PARAMETER"
>*u.ptr</TT
> are
   sent with no processing; the data must be in the format expected by
   the server for binary transmission of the function's argument data
   type.  (The declaration of <TT
CLASS="PARAMETER"
>u.ptr</TT
> as being of
   type <TT
CLASS="TYPE"
>int *</TT
> is historical; it would be better to consider
   it <TT
CLASS="TYPE"
>void *</TT
>.)
   <TT
CLASS="PARAMETER"
>result_buf</TT
> points to the buffer in which to place
   the function's return value.  The caller must have allocated sufficient
   space to store the return value.  (There is no check!) The actual result
   length in bytes will be returned in the integer pointed to by
   <TT
CLASS="PARAMETER"
>result_len</TT
>.  If a 2- or 4-byte integer result
   is expected, set <TT
CLASS="PARAMETER"
>result_is_int</TT
> to 1, otherwise
   set it to 0.  Setting <TT
CLASS="PARAMETER"
>result_is_int</TT
> to 1 causes
   <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> to byte-swap the value if necessary, so that it
   is delivered as a proper <TT
CLASS="TYPE"
>int</TT
> value for the client machine;
   note that a 4-byte integer is delivered into <TT
CLASS="PARAMETER"
>*result_buf</TT
>
   for either allowed result size.
   When <TT
CLASS="PARAMETER"
>result_is_int</TT
> is 0, the binary-format byte string
   sent by the server is returned unmodified. (In this case it's better
   to consider <TT
CLASS="PARAMETER"
>result_buf</TT
> as being of
   type <TT
CLASS="TYPE"
>void *</TT
>.)
  </P
><P
>   <CODE
CLASS="FUNCTION"
>PQfn</CODE
> always returns a valid
   <TT
CLASS="STRUCTNAME"
>PGresult</TT
> pointer. The result status should be
   checked before the result is used.   The caller is responsible for
   freeing  the  <TT
CLASS="STRUCTNAME"
>PGresult</TT
>  with
   <CODE
CLASS="FUNCTION"
>PQclear</CODE
> when it is no longer needed.
  </P
><P
>   Note that it is not possible to handle null arguments, null results,
   nor set-valued results when using this interface.
  </P
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