RE2 – Google Regular Expressions

Project: RE2 GitHub Language: C++

Overview

RE2 is a high-performance, memory-safe regex engine developed by Google. Unlike backtracking engines such as PCRE, RE2 guarantees linear-time execution, making it suitable for online and production systems, even when processing user-provided patterns. It avoids vulnerabilities such as ReDoS (Regular Expression Denial of Service).

RE2 supports a subset of PCRE syntax, including most standard operators, character classes, and captures, but does not support backreferences or complex lookarounds. Its primary design goal is safety and predictability, not complete Perl compatibility.

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Key Features

• Linear-time execution: All regex matching is guaranteed to be O(n) in input size.
• Memory safety: Prevents excessive stack or heap usage even for complex patterns.
• Dynamic usage: Patterns can be compiled at runtime and reused.
• Capture groups: Supports standard capturing and named groups.
• Partial syntax coverage: Supports most common patterns, but lacks backreferences and some advanced lookarounds.

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Typical Use Cases

• Online systems with user-provided regex, such as search engines or filtering tools.
• Large-scale text scanning, log analysis, or real-time event processing.
• Scenarios where performance and safety are more critical than full Perl compatibility.

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Industrial Fit

Requirement	RE2 Support
Online, user-facing safety	✔️
Predictable performance	✔️
Dynamic pattern compilation	✔️
Advanced Perl-only syntax	❌
Captures / group extraction	✔️
Memory-safe	✔️

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C++ Example

#include <re2/re2.h>
#include <iostream>
#include <string>

int main() {
    std::string text = "User: Alice, Score: 42";
    std::string user;
    int score;

    // Compile the regex
    RE2 pattern("User: (\\w+), Score: (\\d+)");

    // Match the text
    if (RE2::FullMatch(text, pattern, &user, &score)) {
        std::cout << "User: " << user << ", Score: " << score << std::endl;
    } else {
        std::cout << "No match found" << std::endl;
    }

    return 0;
}

Explanation:

• RE2::FullMatch checks whether the entire input matches the pattern.
• Captured groups are extracted into variables (user and score).
• RE2 guarantees linear-time execution regardless of input or pattern complexity.