Understanding std::regex declaration : regex_error exception at runtime

Question

I have the following executable. I compile it with gcc 4.7.2 (g++ foo.cc -std=c++11).

At run time, the exception regex_error is thrown.

What am I doing wrong ?

#include <regex>

int main(int, char**){
    std::regex re("\\d");
}

UPDATE The error code in the exception is error_escape. So I tried "\\d". It doesn't fail at runtime, but I doesn't match againt "1", but it DOES match "\d". So this is clearly not what I want

AFAIK, g++ does not support regex yet. Your code, compiled with clang, works perfect. — awesoon, Mar 22 '13 at 16:24
@Lightness Most useful correction I have *ever* seen on stackoverflow! — us2012, Mar 22 '13 at 16:28
Please put your entire testing program, where we can see that it doesn't match "1" but matches "\d". — Roberto, Mar 22 '13 at 16:30
@Fanael, Lightness, thank you for corrections. (Why can't I notice more than one user?) — awesoon, Mar 22 '13 at 16:43
Even with today's release of GCC 4.8 and an updated libstdc++, regex is still broken. You're better off using Boost at this time. — Nathan Ernst, Mar 22 '13 at 21:48

score 2 · Accepted Answer · edited May 23 '17 at 12:24

2

So the answer seem to be that the implementation in the GCC4.7 STL is incomplete. Thank you all for your comments.

No matches with c++11 regex

Thank you soon and Nathan Ernst !

edited May 23 '17 at 12:24

Community

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answered Mar 25 '13 at 11:19

Tristram Gräbener

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score -3 · Answer 2 · answered Mar 22 '13 at 16:22

-3

Why not catch it?

#include <regex>
#include <iostream>

int main(int, char**){
    try {
        std::regex re("\\d");
    } catch(std::exception const& e) {
        std::cout << e.what() << "\n";
    }
}

answered Mar 22 '13 at 16:22

Alex Chamberlain

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How does this explain the exception? – Lightness Races in Orbit Mar 22 '13 at 16:28
@LightnessRacesinOrbit In most cases, `e.what()` will give you a sensible explanation of what's going on... – Alex Chamberlain Mar 22 '13 at 16:32
The OP already knows which exception is being thrown. The question is _why_. – Lightness Races in Orbit Mar 22 '13 at 16:36
1

@LightnessRacesinOrbit http://en.cppreference.com/w/cpp/regex/regex_error suggests that it would give an explanation of what went wrong. – Alex Chamberlain Mar 22 '13 at 16:36
In this case `e.what()` returns `"regex_error"` which is not very helpful. If you catch `std::regex_error` explicitly, you can print out the return value of `e.code()` , which you can decipher by looking at the regex header files. However, in this case all of this is a wild goose chase because there is *nothing wrong with the regular expression* -- in this case, gcc 4.7 just has a very broken implementation of regex that fails almost everything. – Mark Lakata Jun 08 '16 at 17:49

Understanding std::regex declaration : regex_error exception at runtime

2 Answers2