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vector::at() function with example in C++ STL

C++ STL vector::at() function: Here, we are going to learn about the at() function of vector header in C++ STL with example.
Submitted by IncludeHelp, on May 15, 2019

C++ vector::at() function

vector::at() is a library function of "vector" header, it is used to access an element from specified position, it accepts a position/index and returns the reference to the element at specified position/index.

Note: To use vector, include <vector> header.

Syntax

Syntax of vector::at() function

vector::at(size_type n);

Parameter(s)

void – It is a position of an element to be accessed.

Return value

reference – It returns a reference to the element at position n.

Sample Input and Output

Input:
vector<int> vector1{ 1, 2, 3, 4, 5 };

Function call:
cout << vector1.at(0) << endl;
cout << vector1.at(1) << endl;

Output:
1
2

C++ program to demonstrate example of vector::at() function

//C++ STL program to demonstrate example of
//vector::at() function

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> v1{ 10, 20, 30, 40, 50 };

    //accessing elements
    cout << "first element : " << v1.at(0) << endl;
    cout << "second element: " << v1.at(1) << endl;
    cout << "last element  : " << v1.at(v1.size() - 1) << endl;

    //accessing all elemenets
    cout << "all elements of vector v1..." << endl;
    for (int i = 0; i < v1.size(); i++)
        cout << "element at index " << i << " : " << v1.at(i) << endl;

    return 0;
}

Output

first element : 10
second element: 20
last element  : 50
all elements of vector v1...
element at index 0 : 10
element at index 1 : 20
element at index 2 : 30
element at index 3 : 40
element at index 4 : 50

Reference: C++ vector::at()