Programming in C with Linux

C is the programming language most frequently associated with UNIX-like operating systems such as Linux or BSD. Since the 1970s, the bulk of the UNIX operating system and its applications have been written in C. Because the C language doesn't directly rely on any specific hardware architecture, UNIX was one of the first portable operating systems. In other words, the majority of the code that makes up UNIX does not know and doesn't care which computer it is actually running on. Machine-specific features are isolated in a few modules within the Unix kernel, which makes it easy for you to modify them when you are porting to different hardware architectures.

C is a compiled language, which means that your C source code is first analyzed by the preprocessor. It is then translated into assembly language and then into machine instructions that are appropriate to the target CPU. An assembler then creates a binary, or object, file from the machine instructions. Finally, the object file is linked to any required external software support by the linker. A C program is stored in a text file that ends with a .c extension and always contains at least one routine, or function, such as main(), unless the file is an include file (with an .h extension, also known as a header file) containing shared variable definitions or other data or declarations. Functions are the commands that perform each step of the task that the C program was written to accomplish.

Note

The Linux kernel is mostly written in C, which is why Linux works with so many different CPUs. To learn more about building the Linux kernel from source, see Chapter 39, "Kernel and Module Management."

Programming in C++

C++ is an object-oriented extension to C. Because C++ is a superset of C, C++ compilers compile C programs correctly, and it is possible to write non-object-oriented code in C++. The reverse is not true: C compilers cannot compile C++ code.

C++ extends the capabilities of C by providing the necessary features for object-oriented design and code. C++ also provides some features, such as the capability to associate functions with data structures, that do not require the use of class-based object-oriented techniques. For these reasons, the C++ language enables existing UNIX programs to migrate toward the adoption of object orientation over time.

Support for C++ programming using Fedora is provided by gcc, which you run with the name g++ when you are compiling C++ code. KDE includes some intermediate C++ tools, such as moc (the Meta Object Compiler) for use when building KDE applications.

Getting Started with Linux C/C++ Programming

Writing C programs for Linux requires that you understand C syntax, have some understanding of how to interface with the Linux kernel (by using one or more of 1,100 different C functions, known as system calls), and know how to use Linux programming tools such as gcc and make. You'll learn about each of these concepts and processes in this chapter.

To get started, you need to make sure that you have installed all the necessary software development packages (perhaps by using the system-config-packages client; refer to Chapter 7, "Managing Software") to support your project. Installation of basic development software requires more than 50 different software packages and 110MB of hard drive space. If you plan to build programs for the Linux kernel, you need the Kernel development packages and an additional 180MB of storage space (not counting temporary disk space required when building a new kernel).

You should also become familiar with a good text editor. Although GNU purists use the emacs editing environment to write, edit, and compile programs, many other developers do just fine with an editor such as vi or nano for editing source and then use the command line to run development tools.

When programming for GNOME or KDE, you might find it most convenient to use a graphical development project manager, such as GNOME's Glade (the GTK+ User Interface Builder, glade-2), TRolltech's Qt Designer (designer), or KDE's KDevelop (the KDE development environment, kdevelop). These clients allow you to prototype an application with graphical drawing tools, which frees you to concentrate on your client's interface. You can use either to automatically generate all necessary project and source code files for skeletal applications. See the "Graphical Development Tools" section, later in this chapter, for more information.

The Process of Programming

Many Linux C programmers start by writing a program that solves an immediate need, such as a simple command-line program to download or upload phone numbers or other data to a cellular phone or handheld computer. Many beginners get started by becoming proficient in using a Linux text editor, researching any required software routines and reading documentation, browsing available Linux source code, learning how to run a compiler (such as gcc, discussed later in this chapter), and then launching into the iterative process of editing, compiling, executing, and testing.

The following sections in this chapter discuss some of the required or helpful software tools included with Fedora Core. You also see how to create, compile, and run a simple C program and how to use several graphical prototyping tools (such as Glade, Designer, or KDevelop) to shorten the process of developing a user interface for graphical programs. These tools can free up time and effort on those tasks, allowing you to concentrate on the core functions of your new program.