PostgreSQL™ provides a fast-path interface to send simple function calls to the server.
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.
The function PQfn
requests execution of a server function via the fast-path interface:
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;
The fnid
argument is the OID of the function to be
executed. args
and nargs
define the
parameters to be passed to the function; they must match the declared
function argument list. When the isint
field of a
parameter structure is true, the u.integer
value is sent
to the server as an integer of the indicated length (this must be 1,
2, or 4 bytes); proper byte-swapping occurs. When isint
is false, the indicated number of bytes at *u.ptr
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. result_buf
is the buffer in which to
place the return value. The caller must have allocated sufficient
space to store the return value. (There is no check!) The actual result
length will be returned in the integer pointed to by
result_len
. If a 1, 2, or 4-byte integer result
is expected, set result_is_int
to 1, otherwise
set it to 0. Setting result_is_int
to 1 causes
libpq to byte-swap the value if necessary, so that it
is delivered as a proper int value for the client machine.
When result_is_int
is 0, the binary-format byte string
sent by the server is returned unmodified.
PQfn
always returns a valid
PGresult pointer. The result status should be
checked before the result is used. The caller is responsible for
freeing the PGresult with
PQclear
when it is no longer needed.
Note that it is not possible to handle null arguments, null results, nor set-valued results when using this interface.