Vector front() in C++ STL

In C++, the vector front() is a built-in function used to retrieve the first element of the vector. It provides a reference to the first element, allowing you to read or modify it directly.

Let’s take a quick look at a simple example that uses the vector front() method:

#include <bits/stdc++.h>
using namespace std;

int main() {
    vector<int> vec = {11, 23, 45, 9};

    // Printing the first element of the vector
    cout << vec.front();
  
    return 0;
}

11

This article covers the syntax, usage, and common example about the vector front() method in C++ STL:

Syntax of Vector front()

v.front();

Parameters:

• This function does not take any parameter.

Return Value:

• Returns the reference to the first element of the vector container if present.
• If the vector is empty, then the behaviour is undefined.

Examples of vector front()

Modify the First Element of the Vector

#include <bits/stdc++.h>
using namespace std;

int main() {
    vector<int> v = {5, 10, 15, 20};

    // Modify the first element
    v.front() = 50;

    for (int i : v)
        cout << i << " ";
    return 0;
}

50 10 15 20 

Behaviour of Vector front() with Empty Vectors

#include <bits/stdc++.h>
using namespace std;

int main() {
    vector<int> v;

    if (!v.empty()) {
        cout << v.front();
    } else {
        cout << "Vector is empty!";
    }

    return 0;
}

Vector is empty!

Difference Between Vector front() and begin()

The vector front() and begin() both can be used to access the first element of the vector but there are a few differences between them:

In short,

• Use front() for quick, direct access to the first element when no iteration is needed.
• Use begin() when working with iterators or algorithms.