Regex Replace in C++

In C++, you can replace text in a string using the std::regex_replace() function from the <regex> library. This function allows you to search for patterns in a string and replace them with new text.

Basic Replacement

To perform a basic replacement, you need a string, a regex pattern, and a replacement string:

1#include <iostream>
2#include <regex>
3
4int main() {
5  std::string input = "Hello World";
6  std::regex pattern("World");
7  std::string replacement = "Everyone";
8
9  std::string result = std::regex_replace(
10    input, pattern, replacement);
11  std::cout << "Before: " << input <<
12    "\nAfter: " << result;
13}

1Before: Hello World
2After: Hello Everyone

Replacement with Capture Groups

You can also use capture groups in your regex pattern and refer to them in the replacement string using $ followed by the group number:

1#include <iostream>
2#include <regex>
3
4int main() {
5  std::string input = "abc123def456";
6  std::regex pattern("(\\d+)");
7  std::string replacement = "[$1]";
8
9  std::string result = std::regex_replace(
10    input, pattern, replacement);
11  std::cout << "Before: " << input
12    << "\nAfter: " << result;
13}

1Before: abc123def456
2After: abc[123]def[456]

Here, (\d+) captures one or more digits, and [$1] replaces each match with the captured digits enclosed in brackets.

Escaping Special Characters

If your replacement string includes special characters, you need to escape them with a backslash. For example, to include a literal dollar sign in the replacement:

1#include <iostream>
2#include <regex>
3
4int main() {
5  std::string input = "Price: 5 dollars";
6  std::regex pattern("(\\d+) dollars");
7  std::string replacement = "$$ $1";
8
9  std::string result = std::regex_replace(
10    input, pattern, replacement);
11  std::cout << "Before: " << input
12    << "\nAfter: " << result;
13}

1Before: Price: 5 dollars
2After: Price: $ 5

Summary

Using std::regex_replace() in C++ allows you to perform complex string replacements efficiently. Whether you need simple text replacements or advanced modifications using capture groups, std::regex_replace() provides a powerful tool for manipulating strings.