How to Check if a Substring Exists in a Char Array in C++?

In C++, Char array and std::string both are used to store a sequence of characters to represent textual data. In this article, we will learn how to check if a substring exists within a char array in C++.

Example

Input:
charArray[]= "Hello, Geek"
subString="Geek"

Output:
Geek substring is found in char array: Hello, Geek!

Search for a Substring in Char Array

The C++ STL provides the std::find() function to search for a given substring in a range of values.

• If the substring is found, then find() function will return the index of the first occurrence of the given substring.
• If the substring is not found, then std::string::npos (no position) is returned which indicates that the given substring does not exist in a char array.

C++ Program to Search for a Substring in Char Array

// C++ program to check if a substring is present in a char
// array
#include <iostream>
#include <string>
using namespace std;

int main()
{
    // character array
    char char_arr[] = "Hello, Geek!";
    // substring
    const char* sub_string = "Geek";

    // converting character array to string using string
    string char_arr_str = char_arr;

    // use the find method to check substring present or not
    if (char_arr_str.find(sub_string) != string::npos) {
        cout << sub_string
             << " substring is found in char array: "
             << char_arr_str << endl;
    }
    else {
        cout << sub_string
             << " substring is not found in char array: "
             << char_arr_str << endl;
    }

    return 0;
}

Geek substring is found in char array: Hello, Geek!

Time Complexity: O(N * M), where N is the size of the char array and M is the size of the substring.
Auxiliary Space: O(1)

We can also use strstr() function to check if a substring exists in a char array or not.