You may be new to computer programming and wondering what is a code library. When we think of a conventional library an image of a large building with shelves and books come to mind. You then take a book from the shelf category you are interested in and read the information. When it comes to code libraries the concept is very similar but in a virtual, computerised sense.
When building computer applications it is sometimes useful to reuse blocks of code for future projects to save time. The advantages don’t end there, what if you could make use of code that other programmers have written. This is all possible by using code libraries.
So, this is the general concept of why we use a code library. The ability to include prewritten code packaged into a library for use in an application. This in turn greatly reduces the amount of programming time required to build an application. Not only this, a level of standardisation and stability can be introduced by using a code library that is regularly maintained and trusted by the wider development community.
To add, a library of code can be maintained and updated by third-party vendors for updated functionality, improved performance and security with, quite often, minimal changes to the core application that you are working on.
Table of contents
What are code libraries used for?
What is a source code library?
Code library examples
– Python Code Libraries
– JavaScript Code Libraries
– PHP Code Libraries
– Java Code Libraries
– C Code Libraries
What is a library function?
Where can I find free code libraries?
Further code library resources
What are code libraries used for?
Code libraries are used to add extra functionality and features to your core application. In traditional compiled programming languages like C, that may be as simple as enabling the programmer to output text to the computer’s screen. Or possibly the use of mathematical functions when working on equations.
Whatever it may be, the library is a type of extension to the standard capabilities that an application can perform. Generally, this can be referenced by including a line of code, usually in the header of the document to connect (or include) that code library for use. Once in place, classes and functions from the newly introduced library can be invoked for use.
What is a source code library?
A source code library generally refers to the original source of the code before putting through any compilers or generators used to run the application. To make any modifications to an application the source code is required to make those changes.
To emphasise this point a little more I’ll use an analogy of manufacturing a car. The car manufacturer first designs the car and the manufacturing plant is then set up to actually build and manufacture the car based on that design. If modifications need to be made to the car’s design, it won’t work by taking the built car and modifying it, you need to make those changes to the original design so all cars manufactured in the future include the modification.
So in short, the source code library is the original design. Any copies (or compiled versions) are like the manufacturing processing plant as mentioned in the analogy above.
Code library examples
What code libraries look like and how they are used will vary from one programming language to another. Below is a small cross-section of some of the most popular programming languages so you get an idea on a practical level of how various code libraries might be used with a specific language.
Python Code Libraries
Python code libraries are included in the application by using the import statement. A Python library is a collection of one or more modules.
Have a look at the Python standard library that includes built-in functions that can be used by all Python code without the need of an import statement.
Python’s standard library is very extensive, offering a wide range of facilities as indicated by the long table of contents listed below. The library contains built-in modules (written in C) that provide access to system functionality such as file I/O that would otherwise be inaccessible to Python programmers, as well as modules written in Python that provide standardized solutions for many problems that occur in everyday programming.
Source: The Python Standard Library page on the python.org website
If you are interested in creating your own Python library see this article How to create a Python library.
JavaScript Code Libraries
JavaScript is a client-side scripting language that is used in conjunction with HTML. With JavaScript code libraries (or simply JavaScript libraries), an external .js file is included in the head section of the HTML document. The script tag is used to call the JavaScript library file like this…
<script src="libraryfile.js"></script>See javascripting.com for a sizable list of the JavaScript libraries that you can choose from.
PHP Code Libraries
There are a number of ways PHP code libraries can be called into the main PHP script. Usually this is by declaring the library files you are going to use using the include() or require() functions. However if part of a larger application or framework there maybe different methods of achieving this.
Many PHP applications today use code libraries through a package manager called Composer…
Composer is a tool for dependency management in PHP. It allows you to declare the libraries your project depends on and it will manage (install/update) them for you.
Source: Composer Documentation from getcomposer.org
Also, see this article listing some popular PHP libraries to get an idea of what is available, Top 40 PHP Libraries of 2020 Every Developer Should Know.
Java Code Libraries
As an introduction and basic orientation of Java code libraries and packages, w3schools could be a good place to start. The Java Packages page covers the main Java API library which is a set of prewritten classes that are included in the Java Development Environment and also covers the concept of packages.
C Code Libraries
With the C programming language, it’s worth looking at the C standard library to see what is available. This Wikipedia page gives a list of 29 of the header files in the C standard library. Below is some brief code showing the inclusion of the standard input-output header file so the text string “Everything you can imagine is real.” can be displayed to the screen…
#include <stdio.h>
int main()
{
printf("Everything you can imagine is real.");
}What is a library function?
Library functions are prewritten functions contained within a code library that carry out a specific task. For example, with the C programming language, the printf function outputs to the screen as seen in the code example above. To use this function the #include <stdio.h> library header must be declared at the top of the file.
It is the same principle as other programming languages and even custom code libraries. You are referencing a specific function that is contained within the library to perform a certain task.
Where can I find free code libraries?
Depending on the programming language the good majority of code libraries are free. However, it’s worthwhile looking at the licensing a particular code library may be bound by before using it in your application.
Some developers may charge a licence fee for the library they have built but generally, this will come along with additional support. Github has one of the largest repositories of code in the world. See the Version Control Tutorial Videos on Website Library for to get up to speed on GIT and learn more about the open-source community.
Further code library resources
Below is a list of useful resources for researching code libraries. Hopefully, they will provide some additional information on what has been mentioned above and help to consolidate the understanding that you already have gained on this subject.
Code Libraries video on the Computerphile channel – Dr Steve Bagley explores standard programming #INCLUDEs libraries using the C programming language and how they work.
Write Code Libraries in the C Programming Language – A hands-on practical tutorial on how to write code libraries in the C Programming Language.