C++ Vector Library - at() Function


Advertisements

Description

The C++ function std::vector::at() returns reference to the element present at location n in the vector.

Declaration

Following is the declaration for std::vector::at() function form std::vector header.

C++98

reference at (size_type n);
const_reference at (size_type n) const;

Parameters

n − Position of element from container.

Return value

Returns an element from specified location if n is valid vector index.

If vector object is constant qualified then method returns constant reference otherwise it returns non-constant reference.

Exceptions

If n is not valid index out_of_bound exception is thrown.

Time complexity

Constant i.e. O(1)

Example

The following example shows the usage of std::vector::at() function.

#include <iostream>
#include <vector>

using namespace std;

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

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

   return 0;
}

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

1
2
3
4
5
vector.htm
Advertisements