Get an iterator to a specific position in a vector in C++

This post will discuss how to get an iterator to a particular position of a vector in C++.

1. Using + operator

Since an iterator supports the arithmetic operators + and -, we can initialize an iterator to some specific position using the (+) operator, as demonstrated below:

#include <iostream>

#include <vector>

#include <iterator>

using namespace std;

int main()

{

vector<int> ints = { 3, 6, 1, 5, 8 };

int index;

// using normal iterators

index = 2;

std::vector<int>::iterator it = ints.begin() + index;

cout << "Element at index " << index << " is " << *it << endl;

// using constant iterators

index = 4;

std::vector<int>::const_iterator c_itr = ints.cbegin() + index;

cout << "Element at index " << index << " is " << *c_itr;

return 0;

}

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Output:

Element at index 2 is 1
Element at index 4 is 8

2. Using `std::advance` function

Another solution is to get an iterator to the beginning of the vector and then call std::advance to advance the iterator by specific elements.

#include <iostream>

#include <vector>

#include <iterator>

using namespace std;

int main()

{

vector<int> ints = { 3, 6, 1, 5, 8 };

int index;

// using normal iterators

index = 2;

std::vector<int>::iterator it = ints.begin();

std::advance(it, index);

cout << "Element at index " << index << " is " << *it << endl;

// using constant iterators

index = 4;

std::vector<int>::const_iterator c_itr = ints.cbegin();

std::advance(c_itr, index);

cout << "Element at index " << index << " is " << *c_itr;

return 0;

}

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Output:

Element at index 2 is 1
Element at index 4 is 8

3. Using `std::next` function

In C++11 and above, the recommended approach is to use std::next, which advances the specified iterator by the specific number of elements.

#include <iostream>

#include <vector>

#include <iterator>

using namespace std;

int main()

{

vector<int> ints = { 3, 6, 1, 5, 8 };

int index;

// using normal iterators

index = 2;

std::vector<int>::iterator it = std::next(ints.begin(), index);

cout << "Element at index " << index << " is " << *it << endl;

// using constant iterators

index = 4;

std::vector<int>::const_iterator c_itr = std::next(ints.cbegin(), index);

cout << "Element at index " << index << " is " << *c_itr;

return 0;

}

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Output:

Element at index 2 is 1
Element at index 4 is 8

That’s all about getting an iterator to a specific position in a vector in C++.

Get an iterator to a specific position in a vector in C++

1. Using + operator

2. Using std::advance function

3. Using std::next function

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2. Using `std::advance` function

3. Using `std::next` function