Is there public API to fetch errcode?

Hi Postgres hackers,
ereport() can accept an error code. For example:
            ereport(FATAL,
                    (errcode(ERRCODE_TOO_MANY_CONNECTIONS),
                     errmsg("number of requested standby connections
exceeds \"max_wal_senders\" (currently %d)",
                            max_wal_senders)));

In this case the error happens during connection initialization, outside
of an SQL query. I.e. PGresult is not available.

I suspect that the error code is available on the client as
PGconn->last_sqlstate however it is private and I can't find any public
API to fetch it.

Does libpq have an API to extract this code?

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Sergey