return codes

How does one check return codes with an embedded sql program? (I dont seem
to find any info on this, in any of the documentation that I have seen).
In other databases, I have checked the values of sqlca.sqlcode or similar
fields. While I see that this field exists, I dont know if postgres is
similar in this request, and I dont know if there is a better source of
examples of using postgres than the docs and Bruce's book.

thanks,

jr