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.
PQsetNoticeProcessor sets a handler for notice and warning messages.
typedef void (*PQnoticeProcessor) (void *arg, const char *message); PQnoticeProcessor PQsetNoticeProcessor(PGconn *conn, PQnoticeProcessor proc, void *arg); |
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. (You can use this pointer 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);
} |
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 current notice-processor pointer for PGconn is copied into the PGresult for possible use by routines like PQgetvalue.