1.8. libpq Control Functions

• PQsetNoticeProcessor Control reporting of notice and warning messages generated by libpq.

  typedef void (*PQnoticeProcessor) (void *arg, const char *message);
  
  PQnoticeProcessor
  PQsetNoticeProcessor(PGconn *conn,
                       PQnoticeProcessor proc,
                       void *arg);

By default, libpq prints "notice" messages from the backend on stderr, as well as a few error messages that it generates by itself. This behavior can be overridden by supplying a callback function that does something else with the messages. The callback function is passed the text of the error message (which includes a trailing newline), plus a void pointer that is the same one passed to PQsetNoticeProcessor. (This pointer can be used to access application-specific state if needed.) The default notice processor is simply

static void
defaultNoticeProcessor(void * arg, const char * message)
{
    fprintf(stderr, "%s", message);
}

To use a special notice processor, call PQsetNoticeProcessor just after creation of a new PGconn object.

The return value is the pointer to the previous notice processor. If you supply a callback function pointer of NULL, no action is taken, but the current pointer is returned.

Once you have set a notice processor, you should expect that that function could be called as long as either the PGconn object or PGresult objects made from it exist. At creation of a PGresult, the PGconn's current notice processor pointer is copied into the PGresult for possible use by routines like PQgetvalue.