C++ Vector Library - operator[] Function

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Description

The C++ function std::vector::operator[] returns a reference to the element present at location n.

Declaration

Following is the declaration for std::vector::operator[] function form std::vector header.

C++98

reference operator[] (size_type n);
const_reference operator[] (size_type n) const;

Parameters

n − Position of an element in container.

Return value

Returns a reference to the element present at location n.

Exceptions

This member funtion never throws exception. If n is not valid index then behavior is undefined.

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::vector::operator[] function.

#include <iostream>
#include <vector>

using namespace std;

int main(void) {   
   vector<int> v = {1, 2, 3, 4, 5};

   for (int i = 0; i < v.size(); ++i)
      cout << v[i] << endl;

   return 0;
}

Let us compile and run the above program, this will produce the following result −

1
2
3
4
5