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### regex_match

    #include <boost/regex.hpp>

The algorithm `regex_match` determines whether a given regular expression matches all of a given character sequence denoted by a pair of bidirectional-iterators, the algorithm is defined as follows, the main use of this function is data input validation.

| Important
Note that the result is true only if the expression matches the whole of the input sequence. If you want to search for an expression somewhere within the sequence then use `regex_search`. If you want to match a prefix of the character string then use `regex_search` with the flag match_continuous set.

    template <class BidirectionalIterator, class Allocator, class charT, class traits>
    bool regex_match(BidirectionalIterator first, BidirectionalIterator last,
                     match_results<BidirectionalIterator, Allocator>& m,
                     const basic_regex <charT, traits>& e,
                     match_flag_type flags = match_default);

    template <class BidirectionalIterator, class charT, class traits>
    bool regex_match(BidirectionalIterator first, BidirectionalIterator last,
                     const basic_regex <charT, traits>& e,
                     match_flag_type flags = match_default);

    template <class charT, class Allocator, class traits>
    bool regex_match(const charT* str, match_results<const charT*, Allocator>& m,
                     const basic_regex <charT, traits>& e,
                     match_flag_type flags = match_default);

    template <class ST, class SA, class Allocator, class charT, class traits>
    bool regex_match(const basic_string<charT, ST, SA>& s,
                     match_results<typename basic_string<charT, ST, SA>::const_iterator, Allocator>& m,
                     const basic_regex <charT, traits>& e,
                     match_flag_type flags = match_default);

    template <class charT, class traits>
    bool regex_match(const charT* str,
                     const basic_regex <charT, traits>& e,
                     match_flag_type flags = match_default);

    template <class ST, class SA, class charT, class traits>
    bool regex_match(const basic_string<charT, ST, SA>& s,
                     const basic_regex <charT, traits>& e,
                     match_flag_type flags = match_default);

##### Description

    template <class BidirectionalIterator, class Allocator, class charT, class traits>
    bool regex_match(BidirectionalIterator first, BidirectionalIterator last,
                     match_results<BidirectionalIterator, Allocator>& m,
                     const basic_regex <charT, traits>& e,
                     match_flag_type flags = match_default);

Requires: Type BidirectionalIterator meets the requirements of a Bidirectional Iterator (24.1.4).

Effects: Determines whether there is an exact match between the regular expression e, and all of the character sequence [first, last), parameter flags (see `match_flag_type`) is used to control how the expression is matched against the character sequence. Returns true if such a match exists, false otherwise.

Throws: `std::runtime_error` if the complexity of matching the expression against an N character string begins to exceed O(N2), or if the program runs out of stack space while matching the expression (if Boost.Regex is configured in recursive mode), or if the matcher exhausts its permitted memory allocation (if Boost.Regex is configured in non-recursive mode).

Postconditions: If the function returns false, then the effect on parameter m is undefined, otherwise the effects on parameter m are given in the table:

Element | Value
--- | ---
`m.size()` | `1 + e.mark_count()`
`m.empty()` | `false`
`m.prefix().first` | `first`
`m.prefix().last` | `first`
`m.prefix().matched` | `false`
`m.suffix().first` | `last`
`m.suffix().last` | `last`
`m.suffix().matched` | `false`
`m[0].first` | `first`
`m[0].second` | `last`
`m[0].matched` | true if a full match was found, and false if it was a partial match (found as a result of the match_partial flag being set).
`m[n].first` | For all integers `n < m.size()`, the start of the sequence that matched sub-expression n. Alternatively, if sub-expression n did not participate in the match, then `last`.
`m[n].second` | For all integers `n < m.size()`, the end of the sequence that matched sub-expression n. Alternatively, if sub-expression n did not participate in the match, then `last`.
`m[n].matched` | For all integers `n < m.size()`, true if sub-expression n participated in the match, false otherwise.

    template <class BidirectionalIterator, class charT, class traits>
    bool regex_match(BidirectionalIterator first, BidirectionalIterator last,
                   const basic_regex <charT, traits>& e,
                   match_flag_type flags = match_default);

Effects: Behaves "as if" by constructing an instance of `match_results<BidirectionalIterator> what`, and then returning the result of `regex_match(first, last, what, e, flags)`.

    template <class charT, class Allocator, class traits>
    bool regex_match(const charT* str, match_results<const charT*, Allocator>& m,
                   const basic_regex <charT, traits>& e,
                   match_flag_type flags = match_default);

Effects: Returns the result of `regex_match(str, str + char_traits<charT>::length(str), m, e, flags)`.

    template <class ST, class SA, class Allocator,
             class charT, class traits>
    bool regex_match(const basic_string<charT, ST, SA>& s,
                   match_results<typename basic_string<charT, ST, SA>::const_iterator, Allocator>& m,
                   const basic_regex <charT, traits>& e,
                   match_flag_type flags = match_default);

Effects: Returns the result of `regex_match(s.begin(), s.end(), m, e, flags)`.

    template <class charT, class traits>
    bool regex_match(const charT* str,
                   const basic_regex <charT, traits>& e,
                   match_flag_type flags = match_default);

Effects: Returns the result of `regex_match(str, str + char_traits<charT>::length(str), e, flags)`.

    template <class ST, class SA, class charT, class traits>
    bool regex_match(const basic_string<charT, ST, SA>& s,
                   const basic_regex <charT, traits>& e,
                   match_flag_type flags = match_default);

Effects: Returns the result of `regex_match(s.begin(), s.end(), e, flags)`.

##### Examples

The following example processes an ftp response:

    #include <stdlib.h>
    #include <boost/regex.hpp>
    #include <string>
    #include <iostream>

    using namespace boost;

    regex expression("([0-9]+)(\\-| |$)(.*)");

    // process_ftp:
    // on success returns the ftp response code, and fills
    // msg with the ftp response message.
    int process_ftp(const char* response, std::string* msg)
    {
       cmatch what;
       if(regex_match(response, what, expression))
       {
          // what[0] contains the whole string
          // what[1] contains the response code
          // what[2] contains the separator character
          // what[3] contains the text message.
          if(msg)
             msg->assign(what[3].first, what[3].second);
          return std::atoi(what[1].first);
       }
       // failure did not match
       if(msg)
          msg->erase();
       return -1;
    }