unordered_map empty in C++ STL

unordered_map find in C++ STL

Last Updated : 26 Sep, 2024

In C++, std::unordered_map::find function is used to search for a specific element using the key in an unordered map container. It is a member function of std::unordered_map container defined inside <unordered_map> header file.

Syntax

um.find(key);

Parameters

key: The key of the element to be searched.

Return Value

If the given key is found, it returns an iterator to that pair.
Otherwise, it returns the end iterator.

Example of unordered_map::find()

C++

// C++ program to demonstrate how to use 
// unordered_map::find() function
#include <bits/stdc++.h>
using namespace std;

void checkKey(unordered_map<int, string>& um, int key) {
  	 // Searching for element with key
    if (um.find(key) == um.end())
        cout << "Key " << key <<
          " Not Present\n";
    else
        cout << "Key " << key << 
          " Present\n";
}

int main() {
    unordered_map<int, string> um = {{12, "Geeks"},
                  {678, "Geeksfor"}, {88, "Gfg"}};

    // Key1 and key2 which have to search
    int key1 = 678;
    int key2 = 456;
	
  	checkKey(um, key1);
  	checkKey(um, key2);
	return 0;
}

Output

Key 678 Present
Key 456 Not Present

Time Complexity: O(1) on average. O(n) in worst case where n is the number of elements.
Space Complexity: O(1)

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