C++ Structs vs Classes

An introduction to structs - an alternative to classes that provides another way to define our own data types.
This lesson is part of the course:

Intro to C++ Programming

Become a software engineer with C++. Starting from the basics, we guide you step by step along the way

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Ryan McCombe
Ryan McCombe

In some of our class examples, we suggested that our objects should have properties like WorldPosition - where that character currently exists in the world.

We could store this as 3 separate properties, eg, an x, y and z co-ordinate. But for situations like this, it is much better to package these things together, as a single object.

This means we need to create a new custom type of data. We've already seen how to do that using a class, but there is an alternative - something called a structure, or struct

struct Vector3 {
  float x;
  float y;
  float z;

class Character {
  Vector3 Location { 0.0f, 0.0f, 0.0f };

What is a Vector3?

A "vector" is a concept from maths and physics. Vectors are the most common way of representing a position within a space.

A custom Vector3 type (sometimes abbreviated to Vec3) is typically how this is done within graphics applications.

The 3 in the type name indicates it is a 3-dimensional vector, used to store a position in a 3D environment.

We go into this concept in more detail in the next chapter.

Test your Knowledge

How could we create a struct that represents a combat ability?

C++ Structs vs Classes

You may be thinking this problem could also be solved by classes. This is completely true - Vector3 could indeed be a class.

In C++, structs and classes are almost identical.

Structs once existed to solve these simple data requirements when we didn't need all the power of a class. However, as the language evolved over time, structs have become more powerful.

They are now just as powerful as classes. Structs can have functions, constructors, inheritance, and everything else that a class has.

The only difference between a struct and a class is that, by default, members of a struct are public whilst in a class, they are private.

However, the C++ community still attaches semantic differences to the two concepts. Even though they're technically almost identical, their usage is commonly different.

Google's style guide offers a good example, and many developers / companies have a similar approach:

  • structs should be used for passive objects that carry data, but lack any functionality other than access/setting the data members.
  • All fields must be public, and accessed directly rather than through getter/setter methods.
  • Methods should not provide behaviour but should only be used to set up the data e.g., constructor, Initialize(), Reset().
  • If more functionality is required, a class is more appropriate.
  • If in doubt, make it a class.

Moreover, the difference between classes and structs may become slightly more important when working within the context of other ecosystems, such as a game engine.

For example, in Unreal, structs have legitimate technical limitations that makes their differences with classes much more significant than what C++ has by default.

Test your Knowledge

What is the main difference between a struct and a class?

Previously, we've seen how built in objects like int and bool allowed us to use operators like + and >= to interact with them.

It would be useful if we had a way to define operators for our custom types too. For example, we'll need the ability to add two of our vectors together.

We could define a function on our struct to facilitate that. It could allow us to add vectors together by doing something like this:


But it would be nice if we could just do it like this instead:

MyFirstVector + MySecondVector;

In the next lesson, we can see how we can update our classes and structs to make these types of interactions possible.

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Ryan McCombe
Ryan McCombe
This lesson is part of the course:

Intro to C++ Programming

Become a software engineer with C++. Starting from the basics, we guide you step by step along the way

Namespaces, Enums and Structs
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This lesson is part of the course:

Intro to C++ Programming

Become a software engineer with C++. Starting from the basics, we guide you step by step along the way

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C++ Operator Overloading

Learn how we can enhance our classes and structs by letting them define their our own operators.
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