C++ Unordered_set::find() Function

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The C++ std::unordered_set::find() function is used to find or search an element with key equivalent to key k in the container and returns an iterator if it is found, otherwise it returns an iterator to unordered_set::end().

The unordered_set is an associative container that contains a set of unique objects of type key. Every operation like insertion, search, and removal in an unordered_set has constant-time complexity.

Syntax

Following is the syntax for std::unordered_set::find() function.

iterator find ( const key_type& k );
const_iterator find ( const key_type& k ) const;

Parameters

• k − It indicates the key to be searched for.

Return Value

It returns an iterator to the element if the specified value is found; otherwise, it returns unordered_set::end if it is not found in the container.

Example 1

Let's look at the following example, where we are going to demonstrate the usage of unordered_set::find() function.

#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;

int main () {
   unordered_set<string> myset = { "sai","ram","krishna" };
   //searching a key "ram"
   unordered_set<string>::const_iterator got = myset.find ("ram");
   if ( got == myset.end() )
      cout << "not found in myset";
   else
      cout << *got << " is in myset";
   cout << endl;
   return 0;
}

Output

If we run the above code it will generate the following output −

ram is in myset

Example 2

Consider the following example, where we are going to check whether the specified key is available or not.

#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;

int main () {
   unordered_set<int> myset = { 10, 100, 1000, 10000 };
   
   if ( myset.find(100) != myset.end() )
      cout<< "100 is available in unordered set! "<<endl;
   if ( myset.find(1000) != myset.end() )
      cout<< "1000 is available in unordered set! "<<endl;
   else
      cout<< "specified key is not available in unordered set! "<<endl;
      
   return 0;
}

Output

Following is the output of the above code −

100 is available in unordered set! 
1000 is available in unordered set! 

Example 3

In the following example, we are going to erase the element that is found and display the left over elements.

#include <iostream>
#include <unordered_set>
using namespace std;
 
int main (){
   unordered_set<int> myUset{50, 500, 10, 100, 200};
   unordered_set<int>::iterator it;

   it = myUset.find(50);
   myUset.erase(it);
   myUset.erase(myUset.find(10));

   cout<<"myUset contains: ";
   for(it = myUset.begin(); it != myUset.end(); ++it)
      cout<<*it<<" ";

   return 0;
}

Output

Output of the above code is as follows −

myUset contains: 200 100 500