Quite often the public interface of a library that you are interested in is written in a different programming language than the one you use. You will need an interface library that bridges the gap between both languages. This is the case with SQLite, a lightweight database management system [44]. It is written in C and there is a host of libraries to communicate with SQLite in all manner of languages.

For Fortran, there is the fsqlite library that I developed. It was inspired by the work of Al Danial [27], but focused on FORTRAN 77, that was mainly an example of how you could interface to the SQLite library. I wanted a generic solution instead.

The design decisions and the implementation of fsqlite illustrate a more general question: how to combine Fortran and other programming languages? Each time you need to consider:

1. ■ Low-level aspects of the combination:

2. - How do the basic types of the two languages relate to each other?

3. - What are the naming and calling conventions?

4. ■ High-level aspects relating to the actual library: What is a good “model” for the interface? Should you simply write wrapping routines that merely translate the routine interfaces or should you build a higher-level interface, molding the original interface into something that is a better fit for the library's use?

This chapter will cover both types of issues in the context of interfacing with C (an intermediate layer in C is often a convenient way to communicate with any other language) and of the interface to SQLite.