Check if a key is present in a C++ map or unordered_map

Last Updated : 30 Apr, 2024

A C++ map and unordered_map are initialized to some keys and their respective mapped values.
Examples:

Input : 
Map : 1 -> 4, 2 -> 6, 4 -> 6
Check1 : 5, Check2 : 4
Output : 5 : Not present, 4 : Present

C++ implementation :

map

// CPP code to check if a // key is present in a map #include <bits/stdc++.h> using namespace std;  // Function to check if the key is present or not string check_key(map<int, int> m, int key) {     // Key is not present     if (m.find(key) == m.end())         return "Not Present";      return "Present"; }  // Driver int main() {     map<int, int> m;      // Initializing keys and mapped values     m[1] = 4;     m[2] = 6;     m[4] = 6;      // Keys to be checked     int check1 = 5, check2 = 4;      // Function call     cout << check1 << ": " << check_key(m, check1) << '\n';     cout << check2 << ": " << check_key(m, check2); }

unordered_map

// CPP code to check if a key is present  // in an unordered_map #include <bits/stdc++.h> using namespace std;  // Function to check if the key is present or not string check_key(unordered_map<int, int> m, int key) {     // Key is not present     if (m.find(key) == m.end())         return "Not Present";      return "Present"; }  // Driver int main() {     unordered_map<int, int> m;      // Initialising keys and mapped values     m[1] = 4;     m[2] = 6;     m[4] = 6;      // Keys to be checked     int check1 = 5, check2 = 4;      // Function call     cout << check1 << ": " << check_key(m, check1) << '\n';     cout << check2 << ": " << check_key(m, check2); }

Output:

5: Not Present
4: Present

Approach 2nd:

we can also use the count function of the map in c++.

Implementation:

1. Map

C++

// CPP code to check if a // key is present in a map #include <bits/stdc++.h> using namespace std;  // Function to check if the key is present or not using count() string check_key(map<int, int> m, int key) {     // Key is not present     if (m.count(key) == 0)         return "Not Present";      return "Present"; }  // Driver int main() {     map<int, int> m;      // Initializing keys and mapped values     m[1] = 4;     m[2] = 6;     m[4] = 6;      // Keys to be checked     int check1 = 5, check2 = 4;      // Function call     cout << check1 << ": " << check_key(m, check1) << '\n';     cout << check2 << ": " << check_key(m, check2); }

Output:

5: Not Present

4: Present

2. Unordered Map

C++

// CPP code to check if a key is present  // in an unordered_map #include <bits/stdc++.h> using namespace std;  // Function to check if the key is present or not using count() string check_key(unordered_map<int, int> m, int key) {     // Key is not present     if (m.count(key) == 0)         return "Not Present";      return "Present"; }  // Driver int main() {     unordered_map<int, int> m;      // Initialising keys and mapped values     m[1] = 4;     m[2] = 6;     m[4] = 6;      // Keys to be checked     int check1 = 5, check2 = 4;      // Function call     cout << check1 << ": " << check_key(m, check1) << '\n';     cout << check2 << ": " << check_key(m, check2); }