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### 2329. `regex_match()/regex_search()` with `match_results` should forbid temporary strings

Section: 32.3 [re.syn] Status: C++14 Submitter: Stephan T. Lavavej Opened: 2013-09-21 Last 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 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.

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

Proposed resolution:

This wording is relative to N3691.

1. Edit 32.3 [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;
   >       […]
   >     }