Proposed resolution:

This wording is relative to N3691.

1. Edit [re.syn], header <regex> synopsis, as indicated:

   #include <initializer_list>
   
   namespace std {
   
     […]
     
     // 28.11.2, function template regex_match:
     […]
     template <class ST, class SA, class Allocator, class charT, class traits> 
     bool regex_match(const basic_string<charT, ST, SA>&&, 
                      match_results<
                        typename basic_string<charT, ST, SA>::const_iterator, 
                        Allocator>&, 
                      const basic_regex<charT, traits>&, 
                      regex_constants::match_flag_type = 
                        regex_constants::match_default) = delete;
   
     // 28.11.3, function template regex_search:
     […]
     template <class ST, class SA, class Allocator, class charT, class traits> 
     bool regex_search(const basic_string<charT, ST, SA>&&, 
                       match_results<
                         typename basic_string<charT, ST, SA>::const_iterator, 
                         Allocator>&, 
                       const basic_regex<charT, traits>&, 
                       regex_constants::match_flag_type = 
                         regex_constants::match_default) = delete;
     […]
   }
   

[ 2014-02-13 Issaquah: Move as Immediate ]

Consider the following code:

const regex r(R"(meow(\d+)\.txt)");
smatch m;
if (regex_match(dir_iter->path().filename().string(), m, r)) {
  DoSomethingWith(m[1]);
}

This occasionally crashes. The problem is that dir_iter->path().filename().string() returns a temporary string, so the match_results contains invalidated iterators into a destroyed temporary string.

It's fine for regex_match/regex_search(str, reg) to accept temporary strings, because they just return bool. However, the overloads taking match_results should forbid temporary strings.