Ch2.21: struct

Overview

A struct lets you group several values together under a single name. In this chapter, we define the simplest kind of struct: an aggregate. An aggregate contains only data members and has no hidden behavior.

You will learn:

• how to define a struct aggregate
• how to create an object of that type
• how to read and write its members
• how aggregate initialization works

1. Defining a struct aggregate

A struct with only data members is an aggregate.

struct Point {
    int x;
    int y;
};  // ← do not forget this semicolon

The semicolon is required. Forgetting it is a very common beginner mistake.

This defines a new type named Point with two members: x and y.

2. Creating a struct object

You can create a Point using brace initialization:

Point p{3, 4};

This sets p.x = 3 and p.y = 4.

3. Accessing and modifying members

Use the dot operator (.) to read or write members.

Point p{3, 4};

print("x=", p.x, " y=", p.y);

p.x = 10;
p.y = 20;

print("x=", p.x, " y=", p.y);

Each member behaves like a normal variable.

4. Designated initialization

Aggregates support designated initializers:

Point a{.x = 1, .y = 2};

This sets the members by name.

5. What we are not covering yet

In this chapter, we intentionally avoid:

• class
• public / private
• member functions
• constructors
• methods
• containers
• loops

A struct aggregate is simply a group of values with no hidden behavior.

Key takeaways

• A struct with only data members is an aggregate.
• Aggregates support simple brace initialization.
• Members are accessed using ..
• Aggregates contain no hidden behavior.