How to Find the Length of a Substring in a char Array?

In C++, a substring is a string inside another string that is the contiguous part of the string. In this article, we will learn how to find the length of a substring in a char array in C++.

Example

Input: 
str[] = "Hello, World!";
substr= "World";

Output: Length of substring World is: 5

Finding Length of Substring Within Char Array in C++

To find the length of a substring in a char array iterate through the character array and use the std::strstr() function to search for the first occurrence of a substring within a character array if the substring is found calculate its length using the std::string::length() function.

C++ Program to Find Length of Substring in a Char Array

The below example demonstrates how we can find the length of the given substring in a char array.

C++

// C++ Program to find length of a substring in a char array

#include <cstring> // For strstr
#include <iostream>
#include <string> // For std::string

using namespace std;

// Function to find the length of a substring within a char
// array
int findLen(const char* str, const string& substr)
{
    // Search for the substring in the char array
    const char* found = strstr(str, substr.c_str());
    if (found != nullptr) {
        // If found, return the length of the substring
        return substr.length();
    }
    else {
        // If not found, return -1
        return -1;
    }
}

int main()
{
    // Example usage
    const char* str = "Hello, World!. This is GeeksforGeeks";
    string substr = "World";

    // Find the length of the substring
    int length = findLen(str, substr);

    // Output the result
    if (length != -1) {
        cout << "Length of the substring '" << substr
             << "': " << length << endl;
    }
    else {
        cout << "Substring not found." << endl;
    }

    return 0;
}

Output

Length of the substring 'World': 5

Time Complexity: O(N), here N is the length of parent string.
Auxilliary Space: O(1)