[LLVMbugs] [Bug 22061] New: A match_results returns an incorrect sub_match if the sub_match::matched is false

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=22061

            Bug ID: 22061
           Summary: A match_results returns an incorrect sub_match if the
                    sub_match::matched is false
           Product: libc++
           Version: unspecified
          Hardware: All
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: kariya_mitsuru at hotmail.com
                CC: llvmbugs at cs.uiuc.edu, mclow.lists at gmail.com
    Classification: Unclassified

Created attachment 13607
  --> http://llvm.org/bugs/attachment.cgi?id=13607&action=edit
clang++ -v

Please see the following sample.

====================================== sample code
======================================
#include <iostream>
#include <regex>

int main()
{
    const char s[] = "abc";
    const std::regex re("(\\d+)|(\\w+)");

    std::cmatch m;
    std::regex_search(s, m, re);
    std::cout << std::boolalpha;
    for (size_t i = 0, n = m.size(); i < n; ++i) {
        auto&& sub = m[i];
        std::cout << i << ":" << sub.matched << ", str = '" << sub.str() << "',
"
            "range = [" << sub.first - s << ", " << sub.second - s << ")" <<
std::endl;
    }
}
=========================================================================================
============================= output =============================
0:true, str = 'abc', range = [0, 3)
1:false, str = '', range = [-4479204, -4479204)
2:true, str = 'abc', range = [0, 3)
==================================================================

cf. http://melpon.org/wandbox/permlink/42XecnPeRQGI1tAV


The C++11 standard 28.10[re.results]/p.4 says, "Otherwise matched is false, and
members first and second point to the end of the sequence that was searched."

So, I think that the output should be 

============================= output =============================
0:true, str = 'abc', range = [0, 3)
1:false, str = '', range = [3, 3)
2:true, str = 'abc', range = [0, 3)
==================================================================

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