Function pqBuildErrorMessage3

src/interfaces/libpq/fe-protocol3.c:1182–1345

* Construct an error message from the fields in the given PGresult, * appending it to the contents of "msg". */

 * appending it to the contents of "msg".
 */
void
pqBuildErrorMessage3(PQExpBuffer msg, const PGresult *res,
					 PGVerbosity verbosity, PGContextVisibility show_context)
{
	const char *val;
	const char *querytext = NULL;
	int			querypos = 0;

	/* If we couldn't allocate a PGresult, just say "out of memory" */
	if (res == NULL)
	{
		appendPQExpBufferStr(msg, libpq_gettext("out of memory\n"));
		return;
	}

	/*
	 * If we don't have any broken-down fields, just return the base message.
	 * This mainly applies if we're given a libpq-generated error result.
	 */
	if (res->errFields == NULL)
	{
		if (res->errMsg && res->errMsg[0])
			appendPQExpBufferStr(msg, res->errMsg);
		else
			appendPQExpBufferStr(msg, libpq_gettext("no error message available\n"));
		return;
	}

	/* Else build error message from relevant fields */
	val = PQresultErrorField(res, PG_DIAG_SEVERITY);
	if (val)
		appendPQExpBuffer(msg, "%s:  ", val);

	if (verbosity == PQERRORS_SQLSTATE)
	{
		/*
		 * If we have a SQLSTATE, print that and nothing else.  If not (which
		 * shouldn't happen for server-generated errors, but might possibly
		 * happen for libpq-generated ones), fall back to TERSE format, as
		 * that seems better than printing nothing at all.
		 */
		val = PQresultErrorField(res, PG_DIAG_SQLSTATE);
		if (val)
		{
			appendPQExpBuffer(msg, "%s\n", val);
			return;
		}
		verbosity = PQERRORS_TERSE;
	}

	if (verbosity == PQERRORS_VERBOSE)
	{
		val = PQresultErrorField(res, PG_DIAG_SQLSTATE);
		if (val)
			appendPQExpBuffer(msg, "%s: ", val);
	}
	val = PQresultErrorField(res, PG_DIAG_MESSAGE_PRIMARY);
	if (val)