c++11 regex back references

Question

I don't manage to use back references in regular expression in c++. After trying more esoteric things, I tried this simple script on gcc 4.8.1:

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

using namespace std;

int main() {
    regex e("(..)\\1");
    string s("aaaa");
    if (regex_match(s,e))
        cout << "match" << endl;
    return 0;
}

but it produces a runtime error. I tried various flags in regex_constants like ECMAScript or grep but to no avail. What's wrong with this way of using back references in C++ regex engine?

Just to make sure I was not missing something trivial, I tried this in Java

class TestIt
{
    public static void main (String[] args) throws java.lang.Exception
    {
        final String s = "aaaa";
        final String e = "(..)\\1";
        if (s.matches(e))
            System.out.printf("match");
    }
};

and obviously it prints match as expected, which is reassuring.

just to highlight: he's trying to use back references in the *search* pattern - and not in the *replace* pattern. this is valid in some regex engines. — Karoly Horvath, Feb 23 '14 at 09:54
The regex facilities in libstdc++ are not fully working. Use boost or another regex inplementation until this is fixed, or use libc++. — n. m. could be an AI, Feb 23 '14 at 10:14
I think it depends on your library version. I tried your code on my Mac Xcode 5.0.2 and it worked fine. — Mithrandir, Feb 23 '14 at 10:17
See also this: http://stackoverflow.com/questions/12530406/is-gcc4-7-buggy-about-regular-expressions/12665408#12665408. — Aleph, Feb 23 '14 at 10:29
@Mithrandir as I just learned, libc++ (which is used by llvm compiler, in turn used by Xcode) provides full support for regex, while libstdc++ (used by gcc) only provides partial support for now. — UndefinedBehavior, Feb 23 '14 at 10:49
@UndefinedBehavior: well, i guess will have to wait until GCC 4.9 to enjoy full support. :-( — Mithrandir, Feb 23 '14 at 10:58
Work as expected with clang++/libc++: http://coliru.stacked-crooked.com/a/2d740591ad66d4ad — Cubbi, Feb 23 '14 at 23:11
@UndefinedBehavior: I think you can put that up as an answer. — nhahtdh, Feb 24 '14 at 04:48

score 0 · Accepted Answer · answered Feb 28 '14 at 22:18

0

The regex engine included in gcc (in libstdc++) is not fully working yet. This regex works as expected on clang. So this issue has nothing to do with the way C++ treats regular expressions; rather it depends on the compiler used.

answered Feb 28 '14 at 22:18

UndefinedBehavior

836
1
11
20

Can you given GCC version numbers in which back references don't work? – einpoklum May 01 '16 at 18:51

c++11 regex back references

1 Answers1