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.

How to use const in C++ by Sándor Dargo_468 x 60 copy.png

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

## What are rvalue references?

Let’s start with a quick recap on rvalue references. They were introduced in C++11. Since then, we have referred to the traditional references (marked with one `&`) as lvalue references.

Using rvalue (`&&`) references, we can avoid unnecessary copying by moving the values instead of making an extra copy. However, this method can potentially make the original values unusable. 

```
MyObject a{param1, param2};
MyObject b = std::move(a);
a.foo() // Don't do this, it's unsafe, potentially a is in a default constructed state or worse
```
With the help of rvalue references, we can limit unnecessary copying and implement perfect forwarding functions, thus achieving higher performance and more robust libraries.

If we try to define rvalue references in contrast with lvalue references, we have to define lvalue references first. We can say that an lvalue is an expression whose address can be taken. Therefore, an lvalue reference is a locator value.

An rvalue is an unnamed value that exists only during the evaluation of an expression. In other words, we cannot take the address of an rvalue. An rvalue is not an lvalue.


# What are rvalue references?

Let’s start with a quick recap on rvalue references. They were introduced in C++11. Since then, we have referred to the traditional references (marked with one `&`) as lvalue references.

Using rvalue (`&&`) references, we can avoid unnecessary copying by moving the values instead of making an extra copy. However, this method can potentially make the original values unusable. 

```
MyObject a{param1, param2};
MyObject b = std::move(a);
a.foo() // Don't do this, it's unsafe, potentially a is in a default constructed state or worse
```
With the help of rvalue references, we can limit unnecessary copying and implement perfect forwarding functions, thus achieving higher performance and more robust libraries.

If we try to define rvalue references in contrast with lvalue references, we have to define lvalue references first. We can say that an lvalue is an expression whose address can be taken. Therefore, an lvalue reference is a locator value.

An rvalue is an unnamed value that exists only during the evaluation of an expression. In other words, we cannot take the address of an rvalue. An rvalue is not an lvalue.


Let’s learn about the const rvalue references.


Introduction

Arguments using const

Local Variables

Local Members

Functions

Return Types

const Parameters

const and Smart Pointers

Rvalue References

Summary

const Rvalue References

What are rvalue references?