Check if a string contains a substring in C++

This tutorial will discuss about a unique way to check if a string contains a substring in C++.

To check if a string contains another string or not, we can use the find() function of string class in C++. It returns the index position of first occurrence of the given substring in the string. If the given substring does not exists in the string, then it will return std::string::npos.

We have created a function to check if a string contains a substring or not using the string::find() function,

// Returns True if string contains
// the given sub string.
bool contains(
        const std::string& str,
        const std::string& subString)
{
    // Check if substring exists in string
    return str.find(subString) != std::string::npos;
}

This function accepts two strings as arguments, and returns True if the first string contains the second string. Internally, it uses the std::string::find() function to locate the substring in main string.

Let’s see the complete example,

#include <iostream>
#include <string>

// Returns True if string contains
// the given sub string.
bool contains(
        const std::string& str,
        const std::string& subString)
{
    // Check if substring exists in string
    return str.find(subString) != std::string::npos;
}

int main()
{
    std::string str = "This is a sample text";
    std::string subString = "sample";

    // Check if string contains a substring
    if (contains(str, subString))
    {
        std::cout << "Yes, String contains the substring \n";
    }
    else
    {
        std::cout << "No, String does not contains the substring \n";
    }

    return 0;
}

Output :

Yes, String contains the substring

Summary

Today we learned about several ways to check if a string contains a substring in C++. Thanks.