How to Replace Text in a String Using Regex in C++?

Regular expressions or what we can call regex for short are sequences of symbols and characters that create a search pattern and help us to find specific patterns within a given text. In this article, we will learn how to replace text in a string using regex in C++.

Example

Input:
str = "Hello, World! Hello, GFG!" ; 
text = "Hello";
replace= "Hi";

Output:
Hi, World! Hi, GFG!

Replace Regex Matches in C++ String

To replace a text in a string using regex, we can use the function std::regex_replace(). It is defined inside the <regex> header so we need to include it in our program.

Algorithm

1. Define the main string, string to be replaced and replacement string.
2. Create a regex object of the string you want to replace.
3. Then pass the main string, regex object and replacement string to the regex_replace() function.
4. The function regex_replace() returns a new string with the replacements applied.

C++ Program to Replace Text in a String Using Regex

// C++  program to replace a pattern in a string using
// regex.
#include <iostream>
#include <regex>
#include <string>
using namespace std;

int main()
{
    // target string
    string str = "Hello, World! Hello, GFG!";

    // Pattern string
    string pattern = "Hello";

    // regex object
    regex reg(pattern);

    // replacement string
    string replacement = "Hi";

    // call regex_replace() and store the result
    string result = regex_replace(str, reg, replacement);

    // Output the result
    cout << "Original: " << str << endl;
    cout << "Modified: " << result << endl;

    return 0;
}

Original: Hello, World! Hello, GFG!
Modified: Hi, World! Hi, GFG!

Time Complexity: O(N)
Auxiliary Space: O(N)