Check if a vector is empty in C++

In this article, we will discuss different ways to check if a vector is empty or not in C++.

Table Of Contents

Method 1: using vector::empty()

In C++. the vector class provides a function empty(). It returns true if the calling vector object is empty, otherwise it returns false. Let’s see an example,

#include <vector>
#include <iostream>

using namespace std;

int main()
{
    vector<int> vecObj;

    // Check if a vector is empty
    if ( vecObj.empty() )
    {
        cout<< "Vector is Empty" << endl;
    }
    else
    {
        cout<< "Vector is not Empty" << endl;
    }
    return 0;
}

Output:

Vector is Empty

We created a vector with no elements, therefore the vector::empty() function returned true.

Method 2: using vector::size()

In C++, the vector class provides a function size(). It returns the number fo elements in the calling vector object. If a vector is empty then the vector::size() function will return 0, for that vector object. Let’s see an example,

#include <vector>
#include <iostream>

using namespace std;

int main()
{
    vector<int> vecObj;

    // Check if a vector is empty
    // by confirming if its size is 0
    if ( vecObj.size() == 0)
    {
        cout<< "Vector is Empty" << endl;
    }
    else
    {
        cout<< "Vector is not Empty" << endl;
    }
    return 0;

}

Output:

Vector is Empty

We created a vector with no elements, therefore the vector::size() function returned 0.

Method 3: using vector::begin() & vector::end()

The vector::begin() function returns an iterator that points to the first element of vector. Whereas, the vector::end() function returns an iterator that points one past the last
element in the vector. So, if a vector is empty, then the value returned by the begin() and end() functions will be same for that vector. Let’s see an example,

#include <vector>
#include <iostream>

using namespace std;

int main()
{
    vector<int> vecObj;

    // Check if a vector is empty
    if ( vecObj.begin() == vecObj.end() )
    {
        cout<< "Vector is Empty" << endl;
    }
    else
    {
        cout<< "Vector is not Empty" << endl;
    }
    return 0;

}

Output:

Vector is Empty

Summary

We learned about different ways to check if a vector is empty or not in C++.