Book Image

Linux System Programming Techniques

By : Jack-Benny Persson
Book Image

Linux System Programming Techniques

By: Jack-Benny Persson

Overview of this book

Linux is the world's most popular open source operating system (OS). Linux System Programming Techniques will enable you to extend the Linux OS with your own system programs and communicate with other programs on the system. The book begins by exploring the Linux filesystem, its basic commands, built-in manual pages, the GNU compiler collection (GCC), and Linux system calls. You'll then discover how to handle errors in your programs and will learn to catch errors and print relevant information about them. The book takes you through multiple recipes on how to read and write files on the system, using both streams and file descriptors. As you advance, you'll delve into forking, creating zombie processes, and daemons, along with recipes on how to handle daemons using systemd. After this, you'll find out how to create shared libraries and start exploring different types of interprocess communication (IPC). In the later chapters, recipes on how to write programs using POSIX threads and how to debug your programs using the GNU debugger (GDB) and Valgrind will also be covered. By the end of this Linux book, you will be able to develop your own system programs for Linux, including daemons, tools, clients, and filters.
Table of Contents (14 chapters)

Defining feature test macros

In this recipe, we'll learn what some common POSIX standards are, how and why to use them, and how we specify them using feature test macros.

We have already seen several examples of when we have included either a POSIX standard or some specific C standard. For example, when we used getopt(), we defined _XOPEN_SOURCE 500 at the very top of the source code file (mph-to-kph_v2.c from Chapter 2, Making Your Programs Easy to Script).

A feature test macro controls the definitions that are exposed by system header files. We can leverage this in two ways. Either we can use it to create portable applications by using a feature test macro that prevents us from using non-standard definitions or we can use it the other way around, allowing us to use non-standard definitions.

Getting ready

We will write two small programs in this recipe, str-posix.c and which-c.c. You can either download them from