Gain insights into software design patterns in C, explore their implementation, discover underlying principles, and learn to build a vocabulary for better communication and coding practices.

c.tar.gz

main+customer.c

main+customer.c-copy

watches

customers

observer

Reactor

Reactor-copy

observer-copy

Software design patterns are a valuable tool in any software developer's skill set. However, most design patterns are described in the context of an object-oriented programming language such as C++ or Java. The C language is sadly absent in the pattern literature. This course is here to change that by demonstrating that it is possible to use patterns in C programs and how it adds benefits to C programmers. You will learn why design patterns are more of a communication tool than technical solutions, and how patterns let you build and share a common vocabulary that simplifies communication.

The course presents a number of patterns and explains how to implement them in C. Each pattern is introduced via the problem it solves and the domains where the pattern can be used. We also discuss the underlying design principles as well as the trade-offs when applying the pattern. Finally, the course covers a set of coding idioms that will guide you when applying design patterns in C.

Software Design Patterns in C

Managing dependencies between entities in a software system is crucial to a solid design. In the [previous chapter](https://www.educative.io/courses/software-design-patterns-c/implementing-the-strategy-pattern), we had a look at the **open-closed principle**. Now we’ll turn to another principle for dependency
management and illustrate how both of these principles may be realized in C using the **Observer** pattern.

Returning to the examples used for the **State** pattern, we described techniques for implementing the
behavior of a simple digital stop-watch: 
* Implementing such a watch typically involves the task of fetching
the time from some kind of time source. 
* As the time source probably will be tied to interactions with the
operating system, it is  good to encapsulate it in an abstraction hiding the system-specific parts
to ease unit testing and portability. 
* Similarly, we should encapsulate the internals of the digital stop-watch in a module of its own.
* As the digital stop-watch is responsible for fetching the time
from the time-source (to present it on its digital display), it stays clear that there will be a
dependency between the watch and the time-source. There are two obvious choices for the direction
of this dependency.

In this lesson, we will explain the theory of the observer pattern.

Introduction to Pattern in C

The First-Class ADT Pattern

The State Pattern

The Strategy Pattern

The Observer Pattern

The Reactor Pattern

Idiomatic Expressions

Conclusion

Theory of the Observer Pattern

Dependencies arise