C++ Structures

In this page:

What Is a Struct?
Declaring and Using Structs
Structs vs Classes in C++
Nesting and Arrays of Structs
Passing Structs to Functions

What Is a Struct?

A struct in C++ groups related variables of possibly different types under one name, giving you a single unit that models a real-world record like a point, a date, or a book. Unlike a plain array, each member has its own name and type, so you access fields by meaning (book.pages) instead of by numeric index.

Example: What Is a Struct?

cpp

#include <iostream>

struct Point {
	int x;
	int y;
};

int main() {
	Point p = {3, 4};
	std::cout << p.x << "," << p.y << std::endl;
	return 0;
}

Declaring and Using Structs

You declare a struct with the struct keyword followed by a name and a brace-enclosed list of member variables, then create instances the same way you'd declare any other type. Dot notation (.) reaches a member on a struct value, while arrow notation (->) reaches a member through a pointer to a struct.

Example: Declaring and Using Structs

cpp

#include <iostream>

struct Point {
	int x;
	int y;
};

int main() {
	Point p1;
	p1.x = 1;
	p1.y = 2;
	std::cout << p1.x << "," << p1.y << std::endl;
	return 0;
}

Structs vs Classes in C++

Unlike in C, a C++ struct can have constructors, member functions, and even inheritance -- the only real difference from a class is that struct members default to public while class members default to private. Convention still uses struct for simple data-holding types and class for types with real behavior and invariants to protect, even though the compiler treats them almost identically.

Example: Structs vs Classes in C++

cpp

#include <iostream>

struct Point {
	int x;
	Point(int px) : x(px) {} // structs can have constructors too
};

int main() {
	Point p(5); // only real difference from class: public by default
	std::cout << p.x << std::endl;
	return 0;
}

Nesting and Arrays of Structs

Structs can contain other structs as members, letting you build up composite types like an Address inside a Person, and you can declare arrays of structs to hold many records of the same shape in one contiguous block. This is the same pattern used to model rows of tabular data before reaching for a full class hierarchy.

Example: Nesting and Arrays of Structs

cpp

#include <iostream>
#include <string>

struct Address { std::string city; };
struct Person { std::string name; Address addr; };

int main() {
	Person p = {"Alex", {"Delhi"}};
	std::cout << p.name << " lives in " << p.addr.city << std::endl;
	return 0;
}

Passing Structs to Functions

Passing a struct by value copies every member, which is wasteful for large structs, so functions typically take a const StructType& reference to read data without copying or a plain reference to modify the caller's struct in place. Choosing the right passing style here is the same performance consideration that applies to passing any sizeable object in C++.

Example: Passing Structs to Functions

cpp

#include <iostream>

struct Point { int x; int y; };

void printPoint(const Point &p) { // avoids copying every member
	std::cout << p.x << "," << p.y << std::endl;
}

int main() {
	Point p = {3, 4};
	printPoint(p);
	return 0;
}

🔒

Chapter Quiz — Complete all 14 topics to unlock

0/14 topics done

Complete these topics first:

← Previous Lesson C++ Copy Constructor Next Lesson → C++ Enums