Question

In C++ please.

4. Explain why inserting an element into map with insert() is
   considered "safe" while inserting with indexing operator is
   considered "unsafe" with respect to an existing element. Give
   example code which demonstrates the safety of element insert with
   insert()

Answer 1

# Inserting an element into map with insert() is always considered as  "safe" :

In c++ map::insert() is a built-in function (STL) which is used to insert elements with a specific key in the map container.

INSERT is better from the point of safety (it is exceptionally good)

The expression map[key] = value is having two operations:

1. map[key] -           map[key] is used for creating a map element with default value.
2. = value -             value is used for copying the value into that element.

Sometimes an exception may occur at the second step. Then result the operation in that case will be only partially done (a new element was added into map, but that element was not initialized with value pair). In this situation when an operation is not complete, but the system state is modified .

insert operation always gives a strong guarantee, means it will never have side effects because insert is either completely done or it leaves the map in unmodified state.

1. Syntax for insert():

   iterator map_name.insert({key, element})
   

   Parameters: This function accepts a pair of key and element which must be inserted into the map container. if the key already exists in the map then function does not insert the key and element in the map .

   Return Value: The function always returns an iterator pointing to the new element in the container.

# Example code :

#include <bits/stdc++.h>
using namespace std;

int main()
{

  
   map<int, int> mp;     // This line initialize the container

  
   mp.insert({ 2, 30 }); // These lines insert elements in random order
   mp.insert({ 1, 40 });   // These lines insert elements in random order
    mp.insert({ 3, 60 });    // These lines insert elements in random order

    cout << "KEY\tELEMENT\n"; // this line prints the elements
   for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
       cout << itr->first
           << '\t' << itr->second << '\n';
   }
   return 0;
}

Output of the code :

KEY     ELEMENT
1       40
2       30
3       60