11 Interoperability with C: Exposing your app to the web

Pure Fortran is powerful for numerical and array-oriented computation that is ubiquitous in physical sciences and engineering. Howewer, there are quite a few things that aren’t possible in Fortran alone, but can be done in a low-level systems programming language such as C. These include reading and writing data to hardware devices, drawing graphics on the screen in real-time, or sending data over the internet. Interoperability with C allows a programmer to call C functions from Fortran programs. This is important for two reasons: First, enables the above-mentioned low-level functionality, and gives Fortran access to the C ecosystem of libraries. Second, C itself is interoperable with many popular programming languages today, such as Python, JavaScript, Go, or Rust. By using C as the interfacing language, Fortran programs can invoke code written in most other languages, and vice versa. In the real world, this allows Fortran code to be used within web servers, databases, and real-time graphics.

11.1  Interfacing C: Writing a minimal TCP client and server

11.1.1  Introducing networking to Fortran

11.1.2  Installing libdill

11.2  TCP server program: Receiving network connections

11.2.1  IP address data structures

11.2.2  Initializing the IP address structure

11.2.3  Checking IP address values

11.2.4  Intermezzo: Matching compatible C and Fortran data types

11.2.5  Creating a socket and listening for connections

11.2.6  Accepting incoming connections to a socket

11.2.7  Sending a TCP message to the client

11.2.8  Closing a connection

11.3  TCP client program: Connecting to a remote server

11.3.1  Connecting to a remote socket

11.3.2  Receiving a message

11.3.3  The complete client program

11.4  Some interesting mixed Fortran-C projects

11.5  Answer Key

11.5.1  Exercise 1: The Fortran interface to ipaddr_port