1. Why C?

C is a small but extensible language, with software libraries (standard and third party) extending the core language. Among high-level languages, C still sets the mark for performance; hence, C is well suited for applications, especially ones such as database systems and web servers that must perform at a high level. The syntax for C is straightforward, but with an oddity here and there. Anyone who programs in a contemporary high-level language already knows much of C syntax, as other languages have borrowed widely from C.

C is also the dominant systems language: modern operating systems are written mostly in C, with assembly language accounting for the rest. Other programming languages routinely and transparently use standard library routines written in C. For example, when an application written in any other high-level language prints the Hello, world! greeting, it is a C library function that ultimately writes the message to the screen. The standard system libraries for input/output, networking, string processing, mathematics, security, cryptography, data encoding, and so on are likewise written mainly in C. To write a program in C is to write in the system’s native language.

C has been a modern language from the start. The familiar function, which can take arguments and return a value, is the primary code module in C. C exhibits a separation of concerns by distinguishing between interfaces, which describe how functions are called, and implementations, which provide the operational details. As noted, C is naturally and easily extended through software libraries, whether standard or third party. As these libraries become better and richer, so does C. C programmers can create arbitrarily rich data types and data structures and package their own code modules as reusable libraries. C supports higher-order functions (functions that can take functions as arguments) without any special, fussy syntax. This book covers C’s modern features, but always with an eye on C’s close-to-the-metal features.

To understand C is to understand the underlying architecture of a modern computing machine, from an embedded device through a handheld up to a node in a server cluster. C sits atop assembly language, which is symbolic (human-understandable) machine language. Every assembly language is specific to a computer architecture. The assembly language for an Intel device differs from that of an ARM device. Even within an architectural family such as Intel, changes in the architecture are reflected in assembly language. As symbolic machine language, assembly language is approachable, although reading and writing assembly code can be daunting. Assembly language is of interest even to programmers in other languages because it reveals so much about the underlying system. C does not reveal quite as much, but far more than any other high-level language; C also reveals what is common across architectures. One sign of just how close C is to assembly language shows up in compilation: a C compiler can handle any mix of C and assembly source code, and C source is translated first into assembly code. From time to time, it will be useful to compare C source with the assembly source into which the C source translates.

C source code ports well: a C program that compiles on one platform should compile on another, unless platform-specific libraries and data structure sizes come into play. Perfect portability remains an ideal, even for C. C plays still another role—as the lingua franca among programming languages: any language that can talk to C can talk to any other language that does so. Most other languages support C calls in one form or another; a later code example shows how straightforwardly Python can consume library functions written in C.

2. From the Basics Through Advanced Features

The code examples in the book are available at https://github.com/mkalin/cbook.git , and comments are welcome at [email protected].