Overloading Comparison Operators (==, !=, <) and Subscript Operator ([])0%

Overloading Stream Insertion (<<) and Extraction (>>) Operators with friend Functions

Overloading Comparison Operators (==, !=, <) and Subscript Operator ([])

Intermediate13 min read•Updated: 2026-10-22

🔍 Overloading Comparison Operators and the Subscript Operator ([])

Introduction

The subscript operator operator[] enables custom collection classes to be accessed with array-like bracket syntax myCollection[i]. Comparison operators enable searching, sorting, and associative indexing.

🗃️ Implementing `operator[]` (Const & Non-Const Pair)

To provide both read and write capabilities, always implement operator[] as a pair:

1
Non-const version for element mutation: Type& operator[](size_t index)
2
Const version for read-only access: const Type& operator[](size_t index) const

1#include <iostream>
2#include <stdexcept>
3#include <array>
4 
5class IntList {
6private:
7    std::array<int, 5> m_items = {0, 0, 0, 0, 0};
8 
9public:
10    // Non-const: allows assignment: list[0] = 50;
11    int& operator[](std::size_t index) {
12        if (index >= m_items.size()) {
13            throw std::out_of_range("IntList index out of bounds!");
14        }
15        return m_items[index];
16    }
17 
18    // Const: allows reading on const objects: int val = constList[0];
19    const int& operator[](std::size_t index) const {
20        if (index >= m_items.size()) {
21            throw std::out_of_range("IntList index out of bounds!");
22        }
23        return m_items[index];
24    }
25};
26 
27int main() {
28    IntList list;
29    list[0] = 42;
30    list[1] = 84;
31 
32    std::cout << "list[0]: " << list[0] << ", list[1]: " << list[1] << "\n";
33 
34    const IntList& constRef = list;
35    std::cout << "Read via const: " << constRef[0] << "\n";
36    return 0;
37}

🛸 Comparison with C++20 Spaceship Operator (`<=>`)

In C++20, writing comparison operators is as simple as asking the compiler to generate default member-wise comparisons:

1#include <iostream>
2#include <compare>
3 
4struct EmployeeRecord {
5    int id;
6    double salary;
7 
8    // Compiler automatically synthesizes ==, !=, <, <=, >, >=
9    auto operator<=>(const EmployeeRecord&) const = default;
10};
11 
12int main() {
13    EmployeeRecord e1{101, 65000.0};
14    EmployeeRecord e2{102, 72000.0};
15 
16    std::cout << std::boolalpha;
17    std::cout << "e1 < e2 : " << (e1 < e2) << "\n";
18    std::cout << "e1 == e2: " << (e1 == e2) << "\n";
19    return 0;
20}

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Overloading Arithmetic Operators (+, -, *, /)	Overloading Stream Insertion (<<) and Extraction (>>) Operators with friend Functions

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Overloading Stream Insertion (<<) and Extraction (>>) Operators with friend Functions

Overloading Comparison Operators (==, !=, <) and Subscript Operator ([])

Intermediate13 min read•Updated: 2026-10-22

Study Materials

🔍 Overloading Comparison Operators and the Subscript Operator ([])

Introduction

🗃️ Implementing `operator[]` (Const & Non-Const Pair)

To provide both read and write capabilities, always implement operator[] as a pair:

1
Non-const version for element mutation: Type& operator[](size_t index)
2
Const version for read-only access: const Type& operator[](size_t index) const

1#include <iostream>
2#include <stdexcept>
3#include <array>
4 
5class IntList {
6private:
7    std::array<int, 5> m_items = {0, 0, 0, 0, 0};
8 
9public:
10    // Non-const: allows assignment: list[0] = 50;
11    int& operator[](std::size_t index) {
12        if (index >= m_items.size()) {
13            throw std::out_of_range("IntList index out of bounds!");
14        }
15        return m_items[index];
16    }
17 
18    // Const: allows reading on const objects: int val = constList[0];
19    const int& operator[](std::size_t index) const {
20        if (index >= m_items.size()) {
21            throw std::out_of_range("IntList index out of bounds!");
22        }
23        return m_items[index];
24    }
25};
26 
27int main() {
28    IntList list;
29    list[0] = 42;
30    list[1] = 84;
31 
32    std::cout << "list[0]: " << list[0] << ", list[1]: " << list[1] << "\n";
33 
34    const IntList& constRef = list;
35    std::cout << "Read via const: " << constRef[0] << "\n";
36    return 0;
37}

🛸 Comparison with C++20 Spaceship Operator (`<=>`)

In C++20, writing comparison operators is as simple as asking the compiler to generate default member-wise comparisons:

1#include <iostream>
2#include <compare>
3 
4struct EmployeeRecord {
5    int id;
6    double salary;
7 
8    // Compiler automatically synthesizes ==, !=, <, <=, >, >=
9    auto operator<=>(const EmployeeRecord&) const = default;
10};
11 
12int main() {
13    EmployeeRecord e1{101, 65000.0};
14    EmployeeRecord e2{102, 72000.0};
15 
16    std::cout << std::boolalpha;
17    std::cout << "e1 < e2 : " << (e1 < e2) << "\n";
18    std::cout << "e1 == e2: " << (e1 == e2) << "\n";
19    return 0;
20}

Next Lesson

Overloading Stream Insertion (<<) and Extraction (>>) Operators with friend Functions

Continue learning with hands-on practice, examples, and exercises in the upcoming topic.

Related Lessons

Previous Lesson	Next Lesson
Overloading Arithmetic Operators (+, -, *, /)	Overloading Stream Insertion (<<) and Extraction (>>) Operators with friend Functions

Practice Quiz

Test your understanding of this lesson with 1 questions. Each question has one correct answer.

Previous Next

🔍 Overloading Comparison Operators and the Subscript Operator ([])

Introduction

🗃️ Implementing operator[] (Const & Non-Const Pair)

🛸 Comparison with C++20 Spaceship Operator (<=>)

Overloading Stream Insertion (<<) and Extraction (>>) Operators with friend Functions

Related Lessons

Practice Quiz

Loading Page Content...

🔍 Overloading Comparison Operators and the Subscript Operator ([])

Introduction

🗃️ Implementing operator[] (Const & Non-Const Pair)

🛸 Comparison with C++20 Spaceship Operator (<=>)

Overloading Stream Insertion (<<) and Extraction (>>) Operators with friend Functions

Related Lessons

Practice Quiz

🗃️ Implementing `operator[]` (Const & Non-Const Pair)

🛸 Comparison with C++20 Spaceship Operator (`<=>`)

🗃️ Implementing `operator[]` (Const & Non-Const Pair)

🛸 Comparison with C++20 Spaceship Operator (`<=>`)