Get Map Element at Offset in C++ STL

Prerequisites: Map in C++ STL

Since the map is not indexed as arrays or vectors sequential access is not possible in the map but to access an element at a particular offset.

Example: 

inserted elements are { ‘a’,11 } , { ‘b’,12 } , { ‘ c ‘, 13 } 

then we can get { ‘b’, 12 } for 2 position.

Methods to Get Map Element at Offset in C++ STL

• Using an iterator to begin() and offset
• Using advance() function
• Using the next() function 

1. Using an iterator to begin() and offset

The iterator to the begin() is incremented until it reaches the offset using the while loop and then the key-value pair is printed.

C++

// C++ Program to Get
// Map Element At Offset
// using iterator to begin()
// and offset
#include <bits/stdc++.h>
using namespace std;

int main()
{
    // Declaring a map with char ,int
    map<char, int> m;

    // Adding pairs into the map
    m.insert({ 'a', 3 });
    m.insert({ 'g', 2 });
    m.insert({ 'f', 4 });
    m.insert({ 'e', 5 });
    m.insert({ 'd', 4 });
    m.insert({ 'b', 3 });

    int offset = 3;
    auto itr = m.begin();

    int k = 0;

    // Iterate while k is <offset
    while (k < offset) {
        k++;
        itr++;
    }

    // print the key value pair at offset
    cout << itr->first << " " << itr->second << endl;
}

Output

e 5

2. Using advance() function

Using the advance function the offset is given directly and it directly moves the iterator to the particular offset in the map.

Syntax:

advance(begin_itr,offset)

C++

// C++ Program to Get
// Map Element At Offset
// Using advance()
#include <bits/stdc++.h>
using namespace std;

int main()
{
    // Declaring a map with char ,int
    map<char, int> m;

    // Adding pairs into the map
    m.insert({ 'a', 3 });
    m.insert({ 'g', 2 });
    m.insert({ 'f', 4 });
    m.insert({ 'e', 5 });
    m.insert({ 'd', 4 });
    m.insert({ 'b', 3 });

    int offset = 3;

    auto itr = m.begin();
    advance(itr, offset);
    // print the key value pair at offset

    cout << itr->first << " " << itr->second << endl;
}

Output

e 5

3. Using the next() function

The next() function can be used which takes the beginning iterator and the offset. The return value of the next() function is the pointer to the key-value pair at the particular offset.

Syntax:

next(begin_itr, offset)

C++

// C++ Program to Get
// Map Element At Offset
// Using the next()
#include <bits/stdc++.h>
using namespace std;

int main()
{
    // Declaring a map with char ,int
    map<char, int> m;

    // Adding pairs into the map
    m.insert({ 'a', 3 });
    m.insert({ 'g', 2 });
    m.insert({ 'f', 4 });
    m.insert({ 'e', 5 });
    m.insert({ 'd', 4 });
    m.insert({ 'b', 3 });

    int offset = 3;

    auto itr = m.begin();
    auto nitr = next(itr, offset);

    // print the key value pair at offset
    cout << nitr->first << " " << nitr->second << endl;
}

Output

e 5