C++ Find Index of Substring in String

In this C++ tutorial, you will learn how to find the index of given substring in the string using string::find() function, with examples.

Find index of substring in string in C++

string::find() function returns the index of first occurrence of given substring in this string, if there is an occurrence of substring in this string. If the given substring is not present in this string, find() returns -1.

Syntax

The syntax to find the index of substring substr in string str is

str.find(substr)

We can also specify the starting position start in this string and the length n in this string, from which substring has to be searched.

str.find(substr, start, n)

start is optional. And if start is provided, n is optional.

Examples

1. Get Index of substring in string

In the following program, we take two strings: str and substr, and find the index of first occurrence of substr in str using string::find() function.

C++ Program

#include <iostream>
using namespace std;

int main() {
    string str = "hello world. round world.";
    string substr = "world";
    int index = str.find(substr);
    cout << "Index of substring : " << index << endl;
}

Output

Index of substring : 6
Program ended with exit code: 0

2. Index of substring in string in a specific span of the string

In the following program, we take two strings: str and substr, and find the index of first occurrence of substr in str from a specific start position in str, using string::find() function.

C++ Program

#include <iostream>
using namespace std;

int main() {
    string str = "hello world. round world.";
    string substr = "world";
    int start = 8;
    int index = str.find(substr, start);
    cout << "Index of substring : " << index << endl;
}

Output

Index of substring : 19
Program ended with exit code: 0

Conclusion

In this C++ Tutorial, we learned how to find the first occurrence of a given substring in this string using string::find() function, with examples.