30 Regular expressions library [re]

30.12 Regular expression iterators [re.iter]

30.12.1 Class template regex_­iterator [re.regiter]

1
#
The class template regex_­iterator is an iterator adaptor.
It represents a new view of an existing iterator sequence, by enumerating all the occurrences of a regular expression within that sequence.
A regex_­iterator uses regex_­search to find successive regular expression matches within the sequence from which it was constructed.
After the iterator is constructed, and every time operator++ is used, the iterator finds and stores a value of match_­results<BidirectionalIterator>.
If the end of the sequence is reached (regex_­search returns false), the iterator becomes equal to the end-of-sequence iterator value.
The default constructor constructs an end-of-sequence iterator object, which is the only legitimate iterator to be used for the end condition.
The result of operator* on an end-of-sequence iterator is not defined.
For any other iterator value a const match_­results<BidirectionalIterator>& is returned.
The result of operator-> on an end-of-sequence iterator is not defined.
For any other iterator value a const match_­results<BidirectionalIterator>* is returned.
It is impossible to store things into regex_­iterators.
Two end-of-sequence iterators are always equal.
An end-of-sequence iterator is not equal to a non-end-of-sequence iterator.
Two non-end-of-sequence iterators are equal when they are constructed from the same arguments.
namespace std {
  template<class BidirectionalIterator,
            class charT = typename iterator_traits<BidirectionalIterator>::value_type,
            class traits = regex_traits<charT>>
    class regex_iterator {
    public:
      using regex_type        = basic_regex<charT, traits>;
      using iterator_category = forward_iterator_tag;
      using value_type        = match_results<BidirectionalIterator>;
      using difference_type   = ptrdiff_t;
      using pointer           = const value_type*;
      using reference         = const value_type&;

      regex_iterator();
      regex_iterator(BidirectionalIterator a, BidirectionalIterator b,
                     const regex_type& re,
                     regex_constants::match_flag_type m = regex_constants::match_default);
      regex_iterator(BidirectionalIterator, BidirectionalIterator,
                     const regex_type&&,
                     regex_constants::match_flag_type = regex_constants::match_default) = delete;
      regex_iterator(const regex_iterator&);
      regex_iterator& operator=(const regex_iterator&);
      bool operator==(const regex_iterator&) const;
      const value_type& operator*() const;
      const value_type* operator->() const;
      regex_iterator& operator++();
      regex_iterator operator++(int);

    private:
      BidirectionalIterator                begin;               // exposition only
      BidirectionalIterator                end;                 // exposition only
      const regex_type*                    pregex;              // exposition only
      regex_constants::match_flag_type     flags;               // exposition only
      match_results<BidirectionalIterator> match;               // exposition only
    };
}
2
#
An object of type regex_­iterator that is not an end-of-sequence iterator holds a zero-length match if match[0].matched == true and match[0].first == match[0].second.
[Note
:
For example, this can occur when the part of the regular expression that matched consists only of an assertion (such as '^', '$', '\b', '\B').
— end note
]

30.12.1.1 Constructors [re.regiter.cnstr]

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regex_iterator();
1
#
Effects: Constructs an end-of-sequence iterator.
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regex_iterator(BidirectionalIterator a, BidirectionalIterator b, const regex_type& re, regex_constants::match_flag_type m = regex_constants::match_default);
2
#
Effects: Initializes begin and end to a and b, respectively, sets pregex to addressof(re), sets flags to m, then calls regex_­search(begin, end, match, *pregex, flags).
If this call returns false the constructor sets *this to the end-of-sequence iterator.

30.12.1.2 Comparisons [re.regiter.comp]

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bool operator==(const regex_iterator& right) const;
1
#
Returns: true if *this and right are both end-of-sequence iterators or if the following conditions all hold:
  • (1.1)
    begin == right.begin,
  • (1.2)
    end == right.end,
  • (1.3)
    pregex == right.pregex,
  • (1.4)
    flags == right.flags, and
  • (1.5)
    match[0] == right.match[0];
otherwise false.

30.12.1.3 Indirection [re.regiter.deref]

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const value_type& operator*() const;
1
#
Returns: match.
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const value_type* operator->() const;
2
#
Returns: addressof(match).

30.12.1.4 Increment [re.regiter.incr]

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regex_iterator& operator++();
1
#
Effects: Constructs a local variable start of type BidirectionalIterator and initializes it with the value of match[0].second.
2
#
If the iterator holds a zero-length match and start == end the operator sets *this to the end-of-sequence iterator and returns *this.
3
#
Otherwise, if the iterator holds a zero-length match, the operator calls: 
regex_search(start, end, match, *pregex,
             flags | regex_constants::match_not_null | regex_constants::match_continuous)
If the call returns true the operator returns *this.
Otherwise the operator increments start and continues as if the most recent match was not a zero-length match.
4
#
If the most recent match was not a zero-length match, the operator sets flags to flags | regex_­constants​::​match_­prev_­avail and calls regex_­search(start, end, match, *pregex, flags).
If the call returns false the iterator sets *this to the end-of-sequence iterator.
The iterator then returns *this.
5
#
In all cases in which the call to regex_­search returns true, match.prefix().first shall be equal to the previous value of match[0].second, and for each index i in the half-open range [0, match.size()) for which match[i].matched is true, match.position(i) shall return distance(begin, match[i].​first).
6
#
[Note
:
This means that match.position(i) gives the offset from the beginning of the target sequence, which is often not the same as the offset from the sequence passed in the call to regex_­search.
— end note
]
7
#
It is unspecified how the implementation makes these adjustments.
8
#
[Note
:
This means that a compiler may call an implementation-specific search function, in which case a program-defined specialization of regex_­search will not be called.
— end note
]
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regex_iterator operator++(int);
9
#
Effects: As if by: 
regex_iterator tmp = *this;
++(*this);
return tmp;

30.12.2 Class template regex_­token_­iterator [re.tokiter]

1
#
The class template regex_­token_­iterator is an iterator adaptor; that is to say it represents a new view of an existing iterator sequence, by enumerating all the occurrences of a regular expression within that sequence, and presenting one or more sub-expressions for each match found.
Each position enumerated by the iterator is a sub_­match class template instance that represents what matched a particular sub-expression within the regular expression.
2
#
When class regex_­token_­iterator is used to enumerate a single sub-expression with index -1 the iterator performs field splitting: that is to say it enumerates one sub-expression for each section of the character container sequence that does not match the regular expression specified.
3
#
After it is constructed, the iterator finds and stores a value regex_­iterator<BidirectionalIterator> position and sets the internal count N to zero.
It also maintains a sequence subs which contains a list of the sub-expressions which will be enumerated.
Every time operator++ is used the count N is incremented; if N exceeds or equals subs.size(), then the iterator increments member position and sets count N to zero.
4
#
If the end of sequence is reached (position is equal to the end of sequence iterator), the iterator becomes equal to the end-of-sequence iterator value, unless the sub-expression being enumerated has index -1, in which case the iterator enumerates one last sub-expression that contains all the characters from the end of the last regular expression match to the end of the input sequence being enumerated, provided that this would not be an empty sub-expression.
5
#
The default constructor constructs an end-of-sequence iterator object, which is the only legitimate iterator to be used for the end condition.
The result of operator* on an end-of-sequence iterator is not defined.
For any other iterator value a const sub_­match<BidirectionalIterator>& is returned.
The result of operator-> on an end-of-sequence iterator is not defined.
For any other iterator value a const sub_­match<BidirectionalIterator>* is returned.
6
#
It is impossible to store things into regex_­token_­iterators.
Two end-of-sequence iterators are always equal.
An end-of-sequence iterator is not equal to a non-end-of-sequence iterator.
Two non-end-of-sequence iterators are equal when they are constructed from the same arguments.
namespace std {
  template<class BidirectionalIterator,
            class charT = typename iterator_traits<BidirectionalIterator>::value_type,
            class traits = regex_traits<charT>>
    class regex_token_iterator {
    public:
      using regex_type        = basic_regex<charT, traits>;
      using iterator_category = forward_iterator_tag;
      using value_type        = sub_match<BidirectionalIterator>;
      using difference_type   = ptrdiff_t;
      using pointer           = const value_type*;
      using reference         = const value_type&;

      regex_token_iterator();
      regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
                           const regex_type& re,
                           int submatch = 0,
                           regex_constants::match_flag_type m =
                             regex_constants::match_default);
      regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
                           const regex_type& re,
                           const vector<int>& submatches,
                           regex_constants::match_flag_type m =
                             regex_constants::match_default);
      regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
                           const regex_type& re,
                           initializer_list<int> submatches,
                           regex_constants::match_flag_type m =
                             regex_constants::match_default);
      template<size_t N>
        regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
                             const regex_type& re,
                             const int (&submatches)[N],
                             regex_constants::match_flag_type m =
                               regex_constants::match_default);
      regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
                           const regex_type&& re,
                           int submatch = 0,
                           regex_constants::match_flag_type m =
                             regex_constants::match_default) = delete;
      regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
                           const regex_type&& re,
                           const vector<int>& submatches,
                           regex_constants::match_flag_type m =
                             regex_constants::match_default) = delete;
      regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
                           const regex_type&& re,
                           initializer_list<int> submatches,
                           regex_constants::match_flag_type m =
                             regex_constants::match_default) = delete;
      template<size_t N>
      regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b,
                           const regex_type&& re,
                           const int (&submatches)[N],
                           regex_constants::match_flag_type m =
                             regex_constants::match_default) = delete;
      regex_token_iterator(const regex_token_iterator&);
      regex_token_iterator& operator=(const regex_token_iterator&);
      bool operator==(const regex_token_iterator&) const;
      const value_type& operator*() const;
      const value_type* operator->() const;
      regex_token_iterator& operator++();
      regex_token_iterator operator++(int);

    private:
      using position_iterator =
        regex_iterator<BidirectionalIterator, charT, traits>;   // exposition only
      position_iterator position;                               // exposition only
      const value_type* result;                                 // exposition only
      value_type suffix;                                        // exposition only
      size_t N;                                                 // exposition only
      vector<int> subs;                                         // exposition only
    };
}
7
#
A suffix iterator is a regex_­token_­iterator object that points to a final sequence of characters at the end of the target sequence.
In a suffix iterator the member result holds a pointer to the data member suffix, the value of the member suffix.match is true, suffix.first points to the beginning of the final sequence, and suffix.second points to the end of the final sequence.
8
#
[Note
:
For a suffix iterator, data member suffix.first is the same as the end of the last match found, and suffix​.second is the same as the end of the target sequence.
— end note
]
9
#
The current match is (*position).prefix() if subs[N] == -1, or (*position)[subs[N]] for any other value of subs[N].

30.12.2.1 Constructors [re.tokiter.cnstr]

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regex_token_iterator();
1
#
Effects: Constructs the end-of-sequence iterator.
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regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b, const regex_type& re, int submatch = 0, regex_constants::match_flag_type m = regex_constants::match_default); regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b, const regex_type& re, const vector<int>& submatches, regex_constants::match_flag_type m = regex_constants::match_default); regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b, const regex_type& re, initializer_list<int> submatches, regex_constants::match_flag_type m = regex_constants::match_default); template<size_t N> regex_token_iterator(BidirectionalIterator a, BidirectionalIterator b, const regex_type& re, const int (&submatches)[N], regex_constants::match_flag_type m = regex_constants::match_default);
2
#
Preconditions: Each of the initialization values of submatches is >= -1.
3
#
Effects: The first constructor initializes the member subs to hold the single value submatch.
The second, third, and fourth constructors initialize the member subs to hold a copy of the sequence of integer values pointed to by the iterator range [begin(submatches), end(submatches)).
4
#
Each constructor then sets N to 0, and position to position_­iterator(a, b, re, m).
If position is not an end-of-sequence iterator the constructor sets result to the address of the current match.
Otherwise if any of the values stored in subs is equal to -1 the constructor sets *this to a suffix iterator that points to the range [a, b), otherwise the constructor sets *this to an end-of-sequence iterator.

30.12.2.2 Comparisons [re.tokiter.comp]

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bool operator==(const regex_token_iterator& right) const;
1
#
Returns: true if *this and right are both end-of-sequence iterators, or if *this and right are both suffix iterators and suffix == right.suffix; otherwise returns false if *this or right is an end-of-sequence iterator or a suffix iterator.
Otherwise returns true if position == right.position, N == right.N, and subs == right.subs.
Otherwise returns false.

30.12.2.3 Indirection [re.tokiter.deref]

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const value_type& operator*() const;
1
#
Returns: *result.
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const value_type* operator->() const;
2
#
Returns: result.

30.12.2.4 Increment [re.tokiter.incr]

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regex_token_iterator& operator++();
1
#
Effects: Constructs a local variable prev of type position_­iterator, initialized with the value of position.
2
#
If *this is a suffix iterator, sets *this to an end-of-sequence iterator.
3
#
Otherwise, if N + 1 < subs.size(), increments N and sets result to the address of the current match.
4
#
Otherwise, sets N to 0 and increments position.
If position is not an end-of-sequence iterator the operator sets result to the address of the current match.
5
#
Otherwise, if any of the values stored in subs is equal to -1 and prev->suffix().length() is not 0 the operator sets *this to a suffix iterator that points to the range [prev->suffix().first, prev->suffix().second).
6
#
Otherwise, sets *this to an end-of-sequence iterator.
7
#
Returns: *this
🔗
regex_token_iterator& operator++(int);
8
#
Effects: Constructs a copy tmp of *this, then calls ++(*this).
9
#
Returns: tmp.