Principles of Reuse

How to Write Scalable Code

Rule #2: Don't reinvent the wheel

• Integrate high-quality third-party classes into your code

• Write reusable code. Assume that others will integrate your classes into their applications

Libraries

• Libraries are simply collections of prewritten, precompiled code

  • Procedural languages provide a sets of functions

  • Object Oriented languages provide sets of classes

  • C++ is half and half

Anyone can create a library…

Creating a Library

Creating a C/C++ library is remarkably simple

• Designing a good one is quite hard, but more on that later

• Create your classes, and C functions as normal

• Separate out your function and class declarations into header files

• Separate your function/method implementation into .cpp files

• Do NOT include a main function

• Compile your code with the -c flag

  • This means "compile only", and does not attempt to create a final, executable program… instead you will get one or more object files. (.o files)

Using a Custom Library

To use a library, we simply add the precompiled .a file when we compile the application (the thing with a main method in it)

• You can add as many libraries as you like on the command line

• This provides strong decoupling of library code from application code…

• Different programmers can develop the different parts at different times

C++ Standard Libraries

C++ provides many libraries as standard, above those in C

• <iostream> library that deals with basic input and output

  • Imported using #include <iostream>

  • It serves as a modern alternative to the stdio.h library (printf and scanf)

• <string> library provides the string type

• <regex> <queue> <stack> <list> <map> <strstream> <utility>

From C: 

• <cstring> provides string related functions (string.h) 

• <cmath> provides cos(), sin(), round(), sqrt(), pow() and more

• <cstdlib> provides conversion, memory handling, sorting, search ..

iostream - What’s New

• cin: Equivalent to scanf for input

• cout: Equivalent to printf for output 

• cerr: Used for printing errors 

• clog: Employed for logging purposes

Namespaces

• The C++ standard library uses a namespace call std

• Namespaces provide space where we can define or declare identifiers. i.e. variables, methods and classes

• A namespace is designed to differentiate functions, classes, variables with the same name available in different libraries

• In essence, a namespace also defines a scope

  

The string Class

In C, we represent strings as a null terminated sequence of chars in memory and use a pointer to the start of that memory to refer to it (char *)…

• This can be a bit limiting however…

  • We either used fixed length arrays

  • Or need to deal with dynamic memory allocation (malloc/free)

• C++ wraps this functionality in the string class

• The string class definition can be imported using #include

• string provides access to a wide range of methods useful for string manipulation