How to Capture std::vector in Lambda Function?

In C++, lambda functions allow users to define an inline function anywhere in the program. They are also able to capture the objects from outside its definition. In this article, we will look at how to capture a std::vector object in lambda functions in C++.

Capture std::vector in Lambda Function

To capture the std::vector container object that is present outside of the lambda function definition, we can use the capture clause of the lambda expression. The capture clause allows both capture by value and capture by reference method.

Capture by Value

[vector_name] (args){
    // code
}

Capture by Reference

[&vector_name] (args) {
    // code
}

C++ Program to Capture std::vector in Lambda Function

C++

// C++ program to capture std::vector in a lambda function
#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> vec = { 1, 2, 3, 4, 5 };

    // Lambda function capturing vector by reference
    auto printVector = [&vec]() mutable {
        for (auto elem : vec) {
            cout << elem << " ";
        }
        cout << endl;
    };

    // modifying vector by capturing using value
    auto addVectorV = [vec]() mutable{
        for (auto& elem : vec) {
            elem = elem + 1;
        }
    };

    // modifying vector by capturing using reference
    auto addVectorR = [&vec]() {
        for (auto& elem : vec) {
            elem = elem + 1;
        }
    };

    addVectorV();
    cout << "Original Vector after calling addVectorV: ";
    printVector();

    addVectorR();
    cout << "Original Vector after calling addVectorR: ";
    printVector();

    return 0;
}

Output

Original Vector after calling addVectorV: 1 2 3 4 5 
Original Vector after calling addVectorR: 2 3 4 5 6