C++11 regex end-of-line doesn't match

Question

I can't get the $ (dollar-sign) to work as documented in C++11 regular expressions. This is with ECMAScript syntax (the default).

Example (regex.cc):

#include <iostream>
#include <regex>

int main() {
    if ( std::regex_search("one\ntwo", std::regex{"one$"}) ) {
        std::cout << "Should match, doesn't." << std::endl;
    }

    if ( std::regex_search("one\ntwo", std::regex{"two$"}
                         , std::regex_constants::match_not_eol) ) {
        std::cout << "Shouldn't match, does." << std::endl;
    }

    return 0;
}

Expected output: Should match, doesn't.

Actual output: Shouldn't match, does.

From http://www.cplusplus.com/reference/regex/ECMAScript/:

$ - End of line - Either it is the end of the target sequence, or precedes a line terminator.

From http://www.cplusplus.com/reference/regex/regex_search/:

match_not_eol - Not End-Of-Line - The last character is not considered an end of line ("$" does not match).

Tested with Clang 3.3 and 3.4 on FreeBSD 10:

clang++ -std=c++11 -stdlib=libc++ -o regex regex.cc && ./regex

What am I missing?

Answer 1

Looks like you stumbled on LWG issue 2343

To quote,

If Multiline is true, $ matches just before LineTerminator.

If Multiline is false, $ does not match just before LineTerminator.

[,,,]

Multiline of the existing implementations are as follows:

Multiline=false:

libstdc++ r206594

libc++ r199174

Multiline=true:

Visual Studio Express 2013

boost 1.55

Note: using the current SVN version of libc++, your first test IS actually matched, so looks like this LWG issue is going to be resolved in Multiline's favor

The second issue (match_not_eol ignored) looks like a fairly straightforward implementation bug. Boost.regex doesn't match that test case.