Operating System: Windows 10 1909

MinGW-64: 8.1

I need to use regular expressions in my program to match some simple stuff. At first, I used std::regex, but I found that it crashed when running. It threw an exception.

    
    std::string pattern =  "[abc]";
    try {
        std::cout<<"111111111\n";
        std::regex regexPattern(pattern);
        std::cout<<"222222222\n";
        std::smatch match;

        if (std::regex_match(line, match, regexPattern)) {
            ...
        }
    } catch (const std::exception& e) {
        std::cerr << "regex match error: " << e.what() << std::endl;
        return false;
    }

An exception was thrown

111111111
regex match error: std::bad_alloc

It crashes immediately when creating a std::regex object. It doesn’t match anything at all.

Just like in the code before, I tested letting it match something simple like "[abc]" and it still crashes, but if I let it match something simple like "abc" without brackets, it runs—but that doesn’t really make any sense.

I even made a small program to test using std::regex, but it runs just fine.

#include <iostream>
#include <regex>
#include <string>

int main() {

    try {
        std::regex re("[abc]");
        if (std::regex_search("a", re)) {
            std::cout << "yes 1\n";
        }
    } catch (const std::exception& e) {
        std::cout << "no 1" << e.what() << "\n";
    }
    
    try {
        std::regex re("[a-z]");
        if (std::regex_search("m", re)) {
            std::cout << "yes 2\n";
        }
    } catch (const std::exception& e) {
        std::cout << "no 2" << e.what() << "\n";
    }
    
    return 0;
}

yes 1
yes 2

I don’t know why my program crashes, but the small snippet of code works just fine. I asked AI, and it said that this is a known serious bug in GCC libstdc’s std::regex. The regex implementation in libstdc has a lot of flaws. Some regular expressions will go into infinite recursion/infinite memory allocation when compiled, crazily requesting memory → std::bad_alloc, running out of memory and crashing.

But can something as simple as the regex "[abc]" really make std::regex crash?

In the end, I gave up on using std::regex and used an open-source library called slre for simple regex matching.