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Check vector is empty or not | C++ STL
Here, we are going to learn how to check whether a vector is empty or not in C++ STL (Standard Template Library)? There are two ways to check whether list is empty or not 1) using vector::empty() and 2) vector::size().
Submitted by IncludeHelp, on August 24, 2018
Vector are dynamic arrays in nature, they can resize themselves according to the number of elements, if elements are added or deleted, size or memory of the vector is automatically resized.
There are two methods to check whether a given vector is an empty vector or not.
- Using vector::empty() function
- Using vector::size() function
1) vector::empty() function
It returns true, if vector is empty else it returns false.
Syntax:
vector_name.empty();
Example:
Input:
vector<int> v1{10, 20, 30, 40, 50 };
vector<int> v2{};
Function calls:
v1.empty()
v2.empty()
Output:
false
true
2) vector::size() function
It returns total number of elements of a vector.
Syntax:
vector_name.size();
Example:
Input:
vector<int> v1{10, 20, 30, 40, 50 };
vector<int> v2{};
Function calls:
v1.size()
v2.size()
Output:
5
0
Program 1: (Using vector::empty() function)
#include <iostream>
#include <vector>
using namespace std;
int main() {
//declare and assign a vectors
//non-empty
vector<int> v1{ 10, 20, 30, 40, 50 };
//empty
vector<int> v2{};
//check whether vector are empty or not
//using empty () function
if(v1.empty())
cout << "vector: v1 is an empty vector" << endl;
else
cout << "vector: v1 has " << v1.size () << " elements" << endl;
if (v2.empty ())
cout << "vector: v2 is an empty vector" << endl;
else
cout << "vector: v2 has " << v2.size () << " elements" << endl ;
return 0;
}
Output
vector: v1 has 5 elements
vector: v2 is an empty vector
Program 2: (Using vector::size() function)
#include <iostream>
#include <vector>
using namespace std;
int main() {
//declare and assign a vectors
//non-empty
vector<int> v1{10, 20, 30, 40, 50};
//empty
vector<int> v2{};
//variable to store size
int n = 0;
//check whether vector are empty or not
//using empty () function
n = v1.size () ;
if(n==0)
cout << "Vector: v1 is an empty vector" << endl;
else
cout << "vector: v1 has " << n << " elements" << endl;
n = v2.size ();
if(n==0)
cout << "vector: v2 is an empty vector" << endl;
else
cout << "vector: v2 has " << v2.size () << " elements" << endl ;
return 0;
}
Output
vector: v1 has 5 elements
vector: v2 is an empty vector