How to Do Case-Insensitive Search for a Substring in C++?

// C++ program to perform a case insensitive substring
// search
#include <algorithm>
#include <iostream>
#include <string>

using namespace std;

// Function to compare two characters in a case-insensitive
// manner
bool caseInsensitiveCharCompare(char a, char b)
{
    // Convert both characters to lower case and compare
    // them
    return tolower(a) == tolower(b);
}

// Function to perform a case-insensitive search for a
// substring in a string
bool caseInsensitiveSubstringSearch(const string& str,
                                    const string& substr)
{
    // Use the search function with the case-insensitive
    // character comparison function
    auto it
        = search(str.begin(), str.end(), substr.begin(),
                 substr.end(), caseInsensitiveCharCompare);

    // Return true if the substring was found, false
    // otherwise
    return it != str.end();
}

// Main function
int main()
{
    // Define the string and the substring
    string str = "Hello World";
    string substr = "WORLD";

    // Call the case-insensitive substring search function
    bool found
        = caseInsensitiveSubstringSearch(str, substr);

    // Print the result
    if (found) {
        cout << "Substring found"
             << endl; // If the substring was found
    }
    else {
        cout << "Substring not found"
             << endl; // If the substring was not found
    }

    return 0;
}