Gain insights into the C++ keyword 'const,' its usage in various contexts, and implications when returning pointers and references. Learn about preventing accidental data changes.

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In this course, you will learn about the C++ keyword const and its behaviour under different usage conditions, including local, global and static contexts. This course will help you to understand const and its implications when you attempt to return pointers and references in C++. By the end of the course, you will have a solid grip on const and its usage in preventing any accidental change of data.

Secure Coding Practices in C++: A Deep Dive into const

# Explanation 

We’ll also encounter some developers who will be reluctant to declare variables, functions, parameters, etc. as `const` "because it doesn’t matter anyway."

In his talk "Rich Code for Tiny Computers", Jason Turner argued for the usage of `const` through an example.

# The Example
In Jason Turner’s example, there is a static array of 16 colors, where each color is represented by a `Color` object, which takes an ID and the red, green, and blue (RGB) components encoded as integers.

Then, the program performs a simple operation on the array of colors... However, the compiler had 350 instructions to complete in this single operation.

During the talk, Turner asked the audience if there were some best practices that they could use to reduce the required overhead. Some suggested using `constexpr`, others recommended precomputed data, but the solution was even simpler.

Turner just had to add `const` to the declaration, and the number of instructions went down from about 350 to 5. No typo there, from 350 to 5! Changing `static std::array<Color, 16> colors {{...}} to static const std::array<Color, 16> colors {{...}}` reduced the required number of instructions by a factor of 70.

"So if you don’t currently use `const` anywhere you can, I bet you will after this talk!", Turner said as he concluded the talk.


Let’s learn why making const variables or parameters matters.


Why does const matter?

Let’s learn why making const variables or parameters matters.

Introduction

Arguments using const

Local Variables

Local Members

Functions

Return Types

const Parameters

const and Smart Pointers

Rvalue References

Summary

Why does const matter?

Explanation

The Example