Lambda Expressions: Syntax, Capture Clauses ([=], [&]), and Predicates

Intermediate13 min read•Updated: 2026-10-22

⚡ Lambda Expressions: Syntax, Capture Clauses, and Predicates

Introduction

A lambda expression is an anonymous function object defined inline at the call site. Introduced in C++11 and refined in Modern C++, lambdas simplify working with STL algorithms.

🧩 Lambda Anatomy

1[ capture-clause ] ( parameters ) -> return-type {
2    // Function body
3};

🎒 The Capture Clause Demystified

The capture clause controls which variables from the enclosing outer scope are accessible inside the lambda:

Capture Clause	Meaning
`[]`	No captures: Can only access parameters passed to the lambda
`[x]`	Captures variable `x` by value (copy)
`[&x]`	Captures variable `x` by reference
`[=]`	Captures all used outer variables by value (copy)
`[&]`	Captures all used outer variables by reference

1#include <iostream>
2#include <vector>
3#include <algorithm>
4 
5int main() {
6    std::vector<int> studentAges = {17, 19, 21, 16, 24, 18, 22};
7    int votingAge = 18;
8 
9    // Capture 'votingAge' by value inside lambda predicate:
10    int adultCount = std::count_if(studentAges.begin(), studentAges.end(), [votingAge](int age) {
11        return age >= votingAge;
12    });
13 
14    std::cout << "Adult Students (>= 18): " << adultCount << "\n";
15 
16    // Modifying external variable via reference capture:
17    int totalYears = 0;
18    std::for_each(studentAges.begin(), studentAges.end(), [&totalYears](int age) {
19        totalYears += age;
20    });
21 
22    std::cout << "Sum of ages: " << totalYears << "\n";
23    return 0;
24}

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Exception Handling with try, catch, and throw

Lambda Expressions: Syntax, Capture Clauses ([=], [&]), and Predicates

Intermediate13 min read•Updated: 2026-10-22

Study Materials

⚡ Lambda Expressions: Syntax, Capture Clauses, and Predicates

Introduction

A lambda expression is an anonymous function object defined inline at the call site. Introduced in C++11 and refined in Modern C++, lambdas simplify working with STL algorithms.

🧩 Lambda Anatomy

1[ capture-clause ] ( parameters ) -> return-type {
2    // Function body
3};

🎒 The Capture Clause Demystified

The capture clause controls which variables from the enclosing outer scope are accessible inside the lambda:

Capture Clause	Meaning
`[]`	No captures: Can only access parameters passed to the lambda
`[x]`	Captures variable `x` by value (copy)
`[&x]`	Captures variable `x` by reference
`[=]`	Captures all used outer variables by value (copy)
`[&]`	Captures all used outer variables by reference

1#include <iostream>
2#include <vector>
3#include <algorithm>
4 
5int main() {
6    std::vector<int> studentAges = {17, 19, 21, 16, 24, 18, 22};
7    int votingAge = 18;
8 
9    // Capture 'votingAge' by value inside lambda predicate:
10    int adultCount = std::count_if(studentAges.begin(), studentAges.end(), [votingAge](int age) {
11        return age >= votingAge;
12    });
13 
14    std::cout << "Adult Students (>= 18): " << adultCount << "\n";
15 
16    // Modifying external variable via reference capture:
17    int totalYears = 0;
18    std::for_each(studentAges.begin(), studentAges.end(), [&totalYears](int age) {
19        totalYears += age;
20    });
21 
22    std::cout << "Sum of ages: " << totalYears << "\n";
23    return 0;
24}

Next Lesson

Exception Handling with try, catch, and throw

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

Related Lessons

Previous Lesson	Next Lesson
Transforming and Accumulating: std::transform, std::accumulate, std::count_if	Exception Handling with try, catch, and throw

Practice Quiz

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

Previous Next