C++ map - at() Function

The C++ map::at function returns a reference to the mapped value of element identified with specified key. If the specified key does not match with key of any element of the map, the function throws an out_of_range exception.

Note: The map::at function produces the same result as operator[] function, except operator[] does not throw an out_of_range exception if the specified key does not match with key of any element of the map.

Syntax

• C++11

mapped_type& at (const key_type& k);
const mapped_type& at (const key_type& k) const;

Parameters

Time Complexity

Logarithmic i.e, Θ(log(n)).

Example:

In the example below, the map::at function is used to get the mapped value of the specified key in MyMap.

#include <iostream>
#include <map>
using namespace std;
 
int main (){
  map<int, string> MyMap;
  map<int, string>::iterator it;

  //populating MyMap
  MyMap[101] = "John";
  MyMap[102] = "Marry";
  MyMap[103] = "Kim";

  //changing the mapped value for key=103
  MyMap.at(103) = "Ramesh";

  //accessing mapped value of specified key
  cout<<"MyMap.at(101) = "<<MyMap.at(101)<<"\n";
  cout<<"MyMap.at(102) = "<<MyMap.at(102)<<"\n";
  cout<<"MyMap.at(103) = "<<MyMap.at(103)<<"\n";

  return 0;
}

The output of the above code will be:

MyMap.at(101) = John
MyMap.at(102) = Marry
MyMap.at(103) = Ramesh