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How to Reverse a String in C++?

How to Match a Pattern in a String in C++?

Last Updated : 04 Mar, 2024

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In C++, strings are sequences of characters stored in a char array. Matching a pattern in a string involves searching for a specific sequence of characters (the pattern) within a given string. In this article, we will learn how to match a pattern in a string in C++.

Example:

Input:
Text: "GeeksForGeeks"
Pattern: "(Geek)(.*)" // Geek followed by any characterOutput:
Pattern matched!

Pattern Matching in C++

To match a pattern in a string we can use regular expressions, which provide a powerful and flexible way to describe and match patterns within strings. C++ provides the <regex> library, which offers support for regular expressions, allowing for more complex pattern matching.

Approach:

Use the std::regex class to create a regular expression object, passing the pattern as a parameter to the constructor.
Use std::regex_search or std::regex_match to search for or match the pattern within the string.
If a match is found print pattern matched.

C++ Program to Match a Pattern in a String

The below program demonstrates how we can match a pattern in a string in C++.

C++

// C++ Program to show how to match a pattern in a string #include <iostream> #include <regex> #include <string> using namespace std;  int main() {     string text = "GeeksForGeeks";      // Define the regular expression pattern to match     regex pattern(         "(Geek)(.*)"); // Geek followed by any character      // Check if the entire string matches the pattern     if (regex_match(text, pattern)) {         // If matched, print message         cout << "Pattern found!" << endl;     }     else {         // If not matched, print message         cout << "Pattern not found!" << endl;     }      return 0; }

Output

Pattern found!

Time Complexity: O(N), here N is the size of the input string.
Auxiliary Space: O(1)

Note: For larger texts or more complex patterns, consider using more efficient string matching algorithms like the Knuth-Morris-Pratt (KMP) algorithm or the Boyer-Moore algorithm. These algorithms can handle larger inputs more effectively.

How to Reverse a String in C++?

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