How to escape a string for use in Boost Regex

Question

I\'m just getting my head around regular expressions, and I\'m using the Boost Regex library.

I have a need to use a regex that includes a specific URL, and it choke

Answer 1

In C++11, you can use raw string literals to avoid escaping the regex string:

std::string myRegex = R"(something\.com)";

See http://en.cppreference.com/w/cpp/language/string_literal, item (6).

Answer 2

. ^ $ | ( ) [ ] { } * + ? \

Ironically, you could use a regex to escape your URL so that it can be inserted into a regex.

const boost::regex esc("[.^$|()\\[\\]{}*+?\\\\]");
const std::string rep("\\\\&");
std::string result = regex_replace(url_to_escape, esc, rep,
                                   boost::match_default | boost::format_sed);

(The flag boost::format_sed specifies to use the replacement string format of sed. In sed, an escape & will output whatever matched by the whole expression)

Or if you are not comfortable with sed's replacement string format, just change the flag to boost::format_perl, and you can use the familiar $& to refer to whatever matched by the whole expression.

const std::string rep("\\\\$&");
std::string result = regex_replace(url_to_escape, esc, rep,
                                   boost::match_default | boost::format_perl);

Answer 3

Using code from Dav (+ a fix from comments), I created ASCII/Unicode function regex_escape():

std::wstring regex_escape(const std::wstring& string_to_escape) {
    static const boost::wregex re_boostRegexEscape( _T("[.^$|()\\[\\]{}*+?\\\\]") );
    const std::wstring rep( _T("\\\\&") );
    std::wstring result = regex_replace(string_to_escape, re_boostRegexEscape, rep, boost::match_default | boost::format_sed);
    return result;
}

For ASCII version, use std::string/boost::regex instead of std::wstring/boost::wregex.

Answer 4

Same with boost::xpressive:

const boost::xpressive::sregex re_escape_text = boost::xpressive::sregex::compile("([\\^\\.\\$\\|\\(\\)\\[\\]\\*\\+\\?\\/\\\\])");

std::string regex_escape(std::string text){
    text = boost::xpressive::regex_replace( text, re_escape_text, std::string("\\$1") );
    return text;
}