Summary

The libpq++ API provides five related classes that you can use to build client applications written in C++:

• PgConnection ” Provides a minimal object that can manage a database connection.

• PgDatabase ” Extends PgConnection with a set of member functions that provide access to a result set.

• PgTransaction ” Extends PgDatabase to provide an automatic transaction context.

• PgCursor ” Extends PgTransaction with member functions that manage a cursor.

• PgLargeObject ” Extends PgConnection with member functions for dealing with large-objects.

You are most likely to use the PgDatabase and PgLargeObject classes in your applications. You might extend the PgConnection class if you want to control the connection process more closely. I recommend that you view the PgTransaction and PgCursor classes as sample code. You probably won't use either of those classes, but you can certainly learn from their implementations .

libpq++ is a wrapper around the libpq C API. If you build your own C++ classes based on PgConnection , you can use the entire libpq API because a PgConnection object contains a PGconn * (and you need a PGConn * to use the libpq API).

At the time I am writing this chapter, another C++ API is appearing in the PostgreSQL community. The libpqxx library is a STL-friendly class library that seems to be much more complete than libpq++. libpqxx provides individual classes for dealing with database connections, transactions, cursors , triggers, and result sets. The classes exported by libpqxx provide a number of convenience features. For example, you can iterate through a result set using array indexing (rather than using explicit member functions).

You can find more information about libpqxx at http:// members .ams.chello.nl/j.vermeulen31/proj-libpqxx.html. By the time this book is published, libpqxx may be an official part of the PostgreSQL distribution.