CV-qualifiers Explained - Understanding const and volatile

CV-qualifiers

0. Preface

Let’s talk about CV-qualifiers! const is for expressing constants, and volatile is for expressing volatile (changeable) types.

In the STL, const and volatile together are defined as CV-qualifiers. Check it out here!

1. Notation

In C++, type qualifiers like CV-qualifiers can appear on both the left and right sides of a type.

Let me show you what I mean:

const int i = 100;
int const i = 100;

If you’re coming from other programming languages, this might be confusing because const is usually written to the left of the type.

In C and C++, both expressions above are correct and identical!

Here’s the key rule: const modifies from right to left, and only when there’s nothing to the left does it modify from left to right.

Why did they design it this way?

Readability Benefits

While the examples above were identical, things get different when dealing with pointers:

const char *const s = "aaa";
char const *const s = "aaa";

Both expressions are the same, but notice how we have two const keywords mixed in. In the first example, one const modifies from left to right, and the other modifies from right to left.

When expressions become complex, consistently placing const on the right (right-to-left modification) makes for much better readability.

Think of it this way:

• char const *const s reads as “s is a const pointer to const char”
• Reading right to left: “s is const, pointing to char that is const”

This convention becomes especially helpful when you’re dealing with more complex pointer declarations. By always putting const on the right side of what it modifies, you can read the declaration from right to left in a consistent manner.

Pro Tips for CV-qualifiers

1. Be Consistent: Choose either left-side or right-side const and stick with it throughout your codebase
2. Right-to-Left Reading: Many C++ experts prefer right-side const because it reads more naturally from right to left
3. Team Standards: Follow your team’s coding standards - consistency matters more than personal preference

Understanding CV-qualifiers properly will make you a better C++ programmer and help you write more maintainable code! 🎯