How to return a vector in c++

In this post, we will see how to return a vector in C++.

vectors can be returned from a function in C++ using two methods: return by value and return by reference. In this article, we will discuss efficient ways to return a vector from a function in C++.

Table of Contents

Return by Value
Return by Reference
Conclusion

Return by Value

It is a preferred method to return vector from function in C++. It can reduce the execution time and space because in this method, an object is not copied for returning a vector. It only points the pointer to the vector which will be returned.

Code:

//Program to return only even elements in a vector

#include <vector>

#include <iostream>

using namespace std;

//Print function

void print_vector(vector<int> &vect)

{ cout<<"Even elements are: ";

for (auto i = vect.begin(); i != vect.end(); ++i)

{cout<< *i << " ";}

}

//Return by value

vector<int> myFunction(vector<int> &results){

vector <int> even_vector;

for (const auto &i : results) {

if(i%2==0){

even_vector.push_back(i);

}

return even_vector;

}

int main(){

vector<int> vec={20, 51, 11, 88, 44, 77, 14, 99};

vector<int> even_vect=myFunction(vec);

print_vector(even_vect);

}

Output:

Even elements are: 20 88 44 14

Return by Reference

This method is better for returning large classes and structures. We will not return the reference of the local variable which is declared in the function because that can lead to dangling reference. In this method, we pass the vector by reference(& myFunction) and we will return as reference only.

Code:

//Program to calculate the squares of the elements in a vector

#include <vector>

#include <iostream>

using namespace std;

//Print function

void print_vector(vector<long> &vect)

{ cout<<"Squares of the elements are: ";

for (auto i = vect.begin(); i != vect.end(); ++i)

{cout<< *i << " ";}

}

//Return by reference

vector<long> &myFunction(vector<long> &results){

for ( auto &i : results) {

i*=i;

}

return results;

}

int main(){

vector<long> vec={20, 51, 11, 88, 44, 77, 14, 99};

vector<long> vect=myFunction(vec);

print_vector(vect);

}

Output:

Squares of the elements are: 400 2601 121 7744 1936 5929 196 9801

Conclusion

In this article we discussed two efficient methods to return vector in C++. We can use return by value for smaller classes or structures. Return by reference method is only useful in the case of large structures and classes.

That’s all about how to return a vector in C++.
Happy Learning!!

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How to return a vector in c++

Return by Value

Further reading:

Vector in C++

Return array from function in C++

Return by Reference

Conclusion

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