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Showing content from https://www.geeksforgeeks.org/cpp/vector-front-in-cpp-stl/ below:

Vector front() in C++ STL

Last Updated : 21 Nov, 2024

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:

C++


 #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;
}

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 C++


 #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;
}

Behaviour of Vector front() with Empty Vectors C++


 #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;
}

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:

Feature Vector front() Vector begin() Purpose Returns a reference to the first element of the vector. Returns an iterator pointing to the first element of the vector. Return Type Reference (T&) or constant reference (const T&). vector<T>::iterator type. Usage Only used for direct access to the first element. Can be used for iteration and access. Syntax v.front(); *v.begin();

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.

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