SQLAPI++ is described as 'C++ library for accessing multiple SQL databases (Oracle, SQL Server, DB2, Sybase, Informix, InterBase, SQLBase, MySQL, PostgreSQL, SQLite, SQL Anywhere and ODBC)' and is an app in the Development category. There are 2 alternatives to SQLAPI++ for Linux, Windows and BSD. The best alternative is Abstract Database Connector, which is both free and Open Source.
Abstract Database Connector is a C/C++ library for making connections to several databases (MySQL, mSQL, PostgreSQL, Interbase, Informix, BDE, ODBC). It runs on Linux, UNIX, BeOS, and Windows, and a dynamic driver loader for ELF OSes is under development.
CppDB is an SQL connectivity library that is designed to provide platform and Database independent connectivity API similarly to what JDBC, ODBC and other connectivity libraries do. http://cppcms.com/sql/cppdb/.