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

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  • Difficulty Level : Basic
  • Last Updated : 11 Oct, 2021
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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);
}

Output:

5: Not Present

4: Present

This article is contributed by Rohit Thapliyal. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 


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