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

Last Updated : 30 Apr, 2024
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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


 


R

Rohit Thapliyal
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