C++ vector::front() Function

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The C++ vector::front() function returns a reference to the first element and was available in the <vector> header file. A segmentation fault error will be returned if we attempt to call the front() function on a vector that is empty.

In contrast to begin() function which returns an iterator pointing to the first element of the vector, the front() function returns a reference to the first element in the vector container. The time complexity of the front() function is constant.

Syntax

Following is the syntax for C++ vector::front() Function −

 reference front();const_reference front() const; 

Parameters

It doesn't accept any kind of parameters.

Example 1

Let's consider the following example, where we are going to use front() function.

 #include <iostream> #include <vector> using namespace std; int main(void) { vector<int> v = {1, 2, 3, 4, 5}; cout << "First element of vector = " << v.front() << endl; return 0; } 

Output

When we compile and run the above program, this will produce the following result −

 First element of vector = 1 

Example 2

Considering the another scenario, where we are going to use the string value and applying the frot() function.

 #include<iostream> #include<vector> using namespace std; int main() { vector<string> myvector{"SHINCHAN","SHEERO","KICK"}; cout<<myvector.front(); return 0; } 

Output

On running the above program, it will produce the following result −

 SHINCHAN 

Example 3

In the following example, we are going to use push_back() function and then applying the front() function.

 #include <iostream> #include <vector> using namespace std; int main(){ vector<int> myvector; myvector.push_back(11); myvector.push_back(33); myvector.push_back(98); cout << myvector.front(); return 0; } 

Output

When we execute the above program, it will produce the following result −

 11 

Example 4

Following is the example, where we are going to do subtraction assignment.

 #include <iostream> #include <vector> int main (){ std::vector<int> tutorial; tutorial.push_back(33); tutorial.push_back(13); tutorial.front() -= tutorial.back(); std::cout << "Element is: " << tutorial.front() << '\n'; return 0; } 

Output

On running the above program, it will produce the following result −

 Element is: 20