C++11 regex throwing std::regex_error

Question

I'm working on a project that requires me to find all theorems in LaTeX source, but I'm having trouble with std::regex:

#include <iostream>
#include <regex>

int main() {
  std::regex r("\\begin{theorem}"); // throws `std::regex_error`

  return 0;
}

I've tried constructing this object with different regex_constants, but it always throws exceptions.

Doing a search on SO shows that there were problems with libstdc++, but they were all from several years ago.

I'm using gcc 5.2.0 from homebrew

Why doesn't this work?

Have you put in a try/catch and printed the message on the exception? — Michael Albers
– Michael Albers, Commented Oct 25, 2015 at 22:41
When I catch it, the output of e.what() is just regex_error. — erip
– erip, Commented Oct 25, 2015 at 22:44
Good ole g++. I suspect you need to escape the "{" and "}" as it's probaly wanting to treat those as meta characters and expecting a number in there instead of text. — Michael Albers
– Michael Albers, Commented Oct 25, 2015 at 22:47
@MichaelAlbers Escaping the curlies seems to have worked. If you add it as an answer, I'll accept it. — erip
– erip, Commented Oct 25, 2015 at 22:50
{ is a metacharacter, the regex engine expects a count or a range after it, like {3}, {3,} or {3,6} for instance — Lucas Trzesniewski
– Lucas Trzesniewski, Commented Oct 25, 2015 at 22:51

Michael Albers · Accepted Answer · 2015-10-25 22:51:25Z

2

You need to escape the { and }. They are being treated as meta characters as in "a{1,3}".

answered Oct 25, 2015 at 22:51

Michael Albers

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