find() in C++ STL

std::find() is a standard algorithm provided by the C++ Standard Template Library (STL). It is used to find the first occurrence of a given value in a specified range. The function works with containers that provide iterators, such as arrays, vectors, lists, and deques.

Example: Using std::find() with sort()

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    vector<int> v = {1, 3, 6, 2, 9};

    // Sorting the vector
    sort(v.begin(), v.end());

    // Search for element 6
    auto it = find(v.begin(), v.end(), 6);

    // Print index
    cout << distance(v.begin(), it);

    return 0;
}

2

Explanation:

• sort(v.begin(), v.end()) sorts the vector in ascending order.
• After sorting, the vector becomes: {1, 2, 3, 6, 9}.
• std::find() performs a linear search to locate the value 6.
• distance() calculates the index of the found element in the sorted vector.
• Even though the container is sorted, std::find() does not use binary search; it still scans elements one by one.

Syntax

The std::find() is a C++ STL function defined inside <algorithm> header file.

std::find(first, last, value);

Parameters:

• first: Iterator to the first element of range.
• last: Iterator to the theoretical element just after the last element of range.
• value: Value to be searched.

Return Value:

• If the value is found, it returns an iterator to its position; otherwise, it returns the end iterator.

The following examples demonstrate the use of find() function for different cases:

Example 1: Search for an Element in the Array

#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[5] = {1, 3, 6, 2, 9};

    // Search an element 6
    auto it = find(arr, arr + 5, 6);

	// Print index
    cout << distance(arr, it);
    return 0;
}

2

Explanation: In this example, the std::find() function returns an iterator pointing to the value 6. The distance() function is then used to determine its index, which is 2.

Example 2: Try to Find an Element That Is Not Present

#include <bits/stdc++.h>
using namespace std;

int main() {
    vector<int> v = {1, 3, 6, 2, 9};

    // Search an element 22
    auto it = find(v.begin(), v.end(), 22);
	
  	// Check if element is present
  	if (it != v.end())
      
    	// Print index
        cout << distance(v.begin(), it);
    else
        cout << "Not Present";
  
    return 0;
}

Not Present

Explanation: If the element is not found, std::find() returns the iterator to the end of the range. By comparing the returned iterator with v.end(), we can determine that the element is not present in the vector.