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2329.regex_match()/regex_search() withmatch_results should forbid temporary strings

Section: 28.6.3[re.syn]Status:C++14Submitter: Stephan T. LavavejOpened: 2013-09-21Last modified: 2016-01-28

Priority:2

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Discussion:

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 thatdir_iter->path().filename().string() returns a temporary string, so thematch_results contains invalidated iterators into a destroyed temporary string.

It's fine forregex_match/regex_search(str, reg) to accept temporary strings, because they just returnbool. However, the overloads takingmatch_results should forbid temporary strings.

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

Proposed resolution:

This wording is relative to N3691.

1. Edit 28.6.3[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;  […]}