C++ Structs vs Classes

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

1struct Vector3 {
2  float x;
3  float y;
4  float z;
5}
6
7class Character {
8  Vector3 Location { 0.0f, 0.0f, 0.0f };
9};
10

1auto Ability {
2  int MinDamage;
3  int MaxDamage;
4  float CritChance;
5}
6

1struct Ability {
2  int MinDamage;
3  int MaxDamage;
4  float CritChance;
5}
6

1typedef Ability {
2  int MinDamage;
3  int MaxDamage;
4  float CritChance;
5}
6

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:

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.

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:

1MyFirstVector.Add(MySecondVector);
2

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

1MyFirstVector + MySecondVector;
2

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