How to Find Substring in String in C++

Jinku Hu Feb 02, 2024

C++ C++ String

Use find Method to Find Substring in a String in C++
Use rfind Method to Find Substring in a String in C++

This article demonstrates methods to find a given substring in a string in C++.

Use `find` Method to Find Substring in a String in C++

The most straightforward way of solving the issue is the find function, which is a built-in string method, and it takes another string object as an argument.

#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl using std::string;

int main() {
  string str1 = "this is random string oiwao2j3";
  string str2 = "oiwao2j3";
  string str3 = "random s tring";

  str1.find(str2) != string::npos
      ? cout << "str1 contains str2" << endl
      : cout << "str1 does not contain str3" << endl;

  str1.find(str3) != string::npos
      ? cout << "str1 contains str3" << endl
      : cout << "str1 does not contain str3" << endl;

  return EXIT_SUCCESS;
}

Output:

str1 contains str2
str1 does not contain str3

Alternatively, you can use find to compare specific character ranges in two strings. To do this, you should pass the starting position and length of the range as arguments to the find method:

#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl using std::string;
using std::stoi;

int main() {
  string str1 = "this is random string oiwao2j3";
  string str3 = "random s tring";
  constexpr int length = 6;
  constexpr int pos = 0;

  str1.find(str3.c_str(), pos, length) != string::npos
      ? cout << length << " chars match from pos " << pos << endl
      : cout << "no match!" << endl;

  return EXIT_SUCCESS;
}

Output:

6 chars match from pos 0

Use `rfind` Method to Find Substring in a String in C++

rfind method has a similar structure as find. We can utilize rfind to find the last substring or specify a certain range to match it with the given substring.

#include <iostream>
#include <string>

using std::cin;
using std::cout;
using std::endl using std::string;
using std::stoi;

int main() {
  string str1 = "this is random string oiwao2j3";
  string str2 = "oiwao2j3";

  str1.rfind(str2) != string::npos
      ? cout << "last occurrence of str3 starts at pos " << str1.rfind(str2)
             << endl
      : cout << "no match!" << endl;

  return EXIT_SUCCESS;
}

Output:

last occurrence of str3 starts at pos 22

Author: Jinku Hu

Founder of DelftStack.com. Jinku has worked in the robotics and automotive industries for over 8 years. He sharpened his coding skills when he needed to do the automatic testing, data collection from remote servers and report creation from the endurance test. He is from an electrical/electronics engineering background but has expanded his interest to embedded electronics, embedded programming and front-/back-end programming.

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Use find Method to Find Substring in a String in C++

Use rfind Method to Find Substring in a String in C++

Related Article - C++ String

Use `find` Method to Find Substring in a String in C++

Use `rfind` Method to Find Substring in a String in C++