## set

    Container

- Summary
- Data Type and Member Function Indexes
- Synopsis
- Description
- Interface
- Constructors
- Destructors
- Assignment Operators
- Allocators
- Iterators
- Member Functions
- Non-member Operators
- Specialized Algorithms
- Example
- Warnings
- See Also

### Summary

An associative container that supports unique keys. A set supports bidirectional iterators.

### Data Type and Member Function Indexes
(exclusive of constructors and destructors)

Member Functions
begin() clear() count() empty() end() equal_range() | erase() find() get_allocator() insert() key_comp() lower_bound() | max_size() operator!=() operator>() operator>=() operator<() operator<=() | operator=() operator==() rbegin() rend() size() swap() upper_bound() value_comp()

### Synopsis

    #include <set>
    template <class Key, class Compare = less<Key>,
    class Allocator = allocator<Key> >
    class set ;

### Description

set<Key, Compare, Allocator> is an associative container that supports unique keys and allows for fast retrieval of the keys. A set contains, at most, one of any key value. The keys are sorted using `Compare`.

Since a set maintains a total order on its elements, you cannot alter the key values directly. Instead, you must insert new elements with an `insert_iterator`.

Any type used for the template parameter `Key` must include the following (where `T` is the `type`, `t` is a `value` of `T` and `u` is a `const` `value` of `T`):

Copy constructors | `T(t)` and `T(u)`
Destructor | `t.~T()`
Address of | `&t` and `&u` yielding `T*` and `const T*` respectively
Assignment | `t = a` where `a` is a (possibly `const`) value of `T`

The `type` used for the `Compare` template parameter must satisfy the requirements for binary functions.

### Interface

    template <class Key, class Compare = less<Key>,
    class Allocator = allocator<Key> >
    class set {
    public:
    // types
    typedef Key key_type;
    typedef Key value_type;
    typedef Compare key_compare;
    typedef Compare value_compare;
    typedef Allocator allocator_type;
    typedef typename Allocator::reference reference;
    typedef typename Allocator::const_reference const_reference;
    class iterator;
    class const_iterator;
    typedef typename Allocator::size_type size_type;
    typedef typename Allocator::difference_type difference_type;
    typedef typename std::reverse_iterator<iterator>
                          reverse_iterator;
    typedef typename std::reverse_iterator<const_iterator>
                          const_reverse_iterator;

    // Construct/Copy/Destroy
    explicit set (const Compare& = Compare(),
                  const Allocator& = Allocator ());
    template <class InputIterator>
    set (InputIterator, InputIterator,
         const Compare& = Compare(),
         const Allocator& = Allocator ());
    set (const set<Key, Compare, Allocator>&);
    ~set ();
    set<Key, Compare, Allocator>& operator=
       (const set <Key, Compare, Allocator>&);
    allocator_type get_allocator () const;

    // Iterators
    iterator begin ();
    const_iterator begin () const;
    iterator end ();
    const_iterator end () const;
    reverse_iterator rbegin ();
    const_reverse_iterator rbegin () const;
    reverse_iterator rend ();
    const_reverse_iterator rend () const;

    // Capacity
    bool empty () const;
    size_type size () const;
    size_type max_size () const;

    // Modifiers
    pair<iterator, bool> insert (const value_type&);
    iterator insert (iterator, const value_type&);
    template <class InputIterator>
    void insert (InputIterator, InputIterator);
    void erase (iterator);
    size_type erase (const key_type&);
    void erase (iterator, iterator);
    void swap (set<Key, Compare, Allocator>&);
    void clear ();

    // Observers
    key_compare key_comp () const;
    value_compare value_comp () const;

    // Set operations
    size_type count (const key_type&) const;
    pair<iterator, iterator> equal_range (const  key_type&) const;
    iterator find (const key_type&) const;
    iterator lower_bound (const key_type&) const;
    iterator upper_bound (const key_type&) const
    };

    // Non-member Operators
    template <class Key, class Compare, class Allocator>
    bool operator== (const set<Key, Compare, Allocator>&,
    const set<Key, Compare, Allocator>&);
    template <class Key, class Compare, class Allocator>
    bool operator!= (const set<Key, Compare, Allocator>&,
    const set<Key, Compare, Allocator>&);
    template <class Key, class Compare, class Allocator>
    bool operator< (const set<Key, Compare, Allocator>&,
    const set<Key, Compare, Allocator>&);
    template <class Key, class Compare, class Allocator>
    bool operator> (const set<Key, Compare, Allocator>&,
    const set<Key, Compare, Allocator>&);
    template <class Key, class Compare, class Allocator>
    bool operator<= (const set<Key, Compare, Allocator>&,
    const set<Key, Compare, Allocator>&);
    template <class Key, class Compare, class Allocator>
    bool operator>= (const set<Key, Compare, Allocator>&,
    const set<Key, Compare, Allocator>&);

    // Specialized Algorithms
    template <class Key, class Compare, class Allocator>
    void swap (set <Key, Compare, Allocator>&,
    set <Key, Compare, Allocator>&);

### Constructors

    explicit
    set(const Compare& comp = Compare(),
    const Allocator& alloc = Allocator());

Creates a set of zero elements. If the function object `comp` is supplied, it is used to compare elements of the set. Otherwise, the default function object in the template argument is used. The template argument defaults to `less (<)`. The allocator alloc is used for all storage management.

    template <class InputIterator>
    set(InputIterator first, InputIterator last,
    const Compare& comp = Compare()
    const Allocator& alloc = Allocator());

Creates a set of length `last - first`, filled with all values obtained by dereferencing the `InputIterators` on the range `[first, last)`. If the function object `comp` is supplied, it is used to compare elements of the set. Otherwise, the default function object in the template argument is used. The template argument defaults to `less (<)`. Uses the allocator Allocator() for all storage management.

    set(const set<Key, Compare, Allocator>& x);

Copy constructor. Creates a copy of `x`.

### Destructors

    ~set();

Releases any allocated memory for self.

### Assignment Operators

    set<Key, Compare, Allocator>&
    operator=(const set<Key, Compare, Allocator>& x);

Returns a reference to self. Self shares an implementation with `x`.

### Allocators

    allocator_type
    get_allocator() const;

Returns a copy of the allocator used by self for storage management.

### Iterators

    iterator
    begin();

Returns an `iterator` that points to the first element in self.

    const_iterator
    begin() const;

Returns a `const_iterator` that points to the first element in self.

    iterator
    end();

Returns an `iterator` that points to the past-the-end value.

    const_iterator
    end() const;

Returns a `const_iterator` that points to the past-the-end value.

    reverse_iterator
    rbegin();

Returns a `reverse_iterator` that points to the past-the-end value.

    const_reverse_iterator
    rbegin() const;

Returns a `const_reverse_iterator` that points to the past-the-end value.

    reverse_iterator
    rend();

Returns a `reverse_iterator` that points to the first element.

    const_reverse_iterator
    rend() const;

Returns a `const_reverse_iterator` that points to the first element.

### Member Functions

    void
    clear();

Erases all elements from the set.

    size_type
    count(const key_type& x) const;

Returns the number of elements equal to `x`. Since a set supports unique keys, `count` always returns `1` or `0`.

    bool
    empty() const;

Returns `true` if the size is zero.

    pair<iterator, iterator>
    equal_range(const key_type&  x) const;

Returns `pair(lower_bound(x),upper_bound(x))`. The `equal_range` function indicates the valid range for insertion of `x` into the set.

    size_type
    erase(const key_type& x);

Deletes all the elements matching `x`. Returns the number of elements erased. Since a set supports unique keys, `erase` always returns `1` or `0`.

    void
    erase(iterator position);

Deletes the map element pointed to by the iterator `position`. Returns an `iterator` pointing to the element following the deleted element, or `end()` if the deleted item was the last one in this list.

    void
    erase(iterator first, iterator last);

Deletes the elements in the range (`first, last`). Returns an `iterator` pointing to the element following the last deleted element, or `end()` if there were no elements after the deleted range.

    iterator
    find(const key_value& x) const;

Returns an `iterator` that points to the element equal to `x`. If there is no such element, the iterator points to the past-the-end value.

    pair<iterator, bool>
    insert(const value_type& x);

Inserts `x` into self according to the comparison function object. The template's default comparison function object is `less (<)`. If the insertion succeeds, it returns a pair composed of the iterator position where the insertion took place and `true`. Otherwise, the pair contains the end value and `false`.

    iterator
    insert(iterator position, const value_type& x);

`x` is inserted into the set. A position may be supplied as a hint regarding where to do the insertion. If the insertion is done right after `position`, then it takes amortized constant time. Otherwise it takes `0 (log N)` time. The return value points to the inserted `x`.

    template <class InputIterator>
    void
    insert(InputIterator first, InputIterator last);

Inserts copies of the elements in the range `[first, last]`.

    key_compare
    key_comp() const;

Returns the comparison function object for the set.

    iterator
    lower_bound(const key_type& x) const;

Returns an `iterator` that points to the first element that is greater than or equal to `x`. If there is no such element, the iterator points to the past-the-end value.

    size_type
    max_size() const;

Returns the size of the largest possible set.

    size_type
    size() const;

Returns the number of elements.

    void
    swap(set<Key, Compare, Allocator>& x);

Exchanges self with `x`.

    iterator
    upper_bound(const key_type& x) const

Returns an iterator that points to the first element that is greater than or equal to `x`. If there is no such element, the iterator points to the past-the-end value.

    value_compare
    value_comp() const;

Returns the set's comparison object. This is identical to the function `key_comp()`.

### Non-member Operators

    template <class Key, class Compare, class Allocator>
    bool operator==(const set<Key, Compare, Allocator>& x,
    const set<Key, Compare, Allocator>& y);

Returns `true` if `x` is the same as `y`.

    template <class Key, class Compare, class Allocator>
    bool operator!=(const set<Key, Compare, Allocator>& x,
    const set<Key, Compare, Allocator>& y);

Returns `!(x==y)`.

    template <class Key, class Compare, class Allocator>
    bool operator<(const set <Key, Compare, Allocator>& x,
    const set <Key, Compare, Allocator>& y);

Returns `true` if the elements contained in `x` are lexicographically less than the elements contained in `y`.

    template <class Key, class Compare, class Allocator>
    bool operator>(const set <Key, Compare, Allocator>& x,
    const set <Key, Compare, Allocator>& y);

Returns `y < x`.

    template <class Key, class Compare, class Allocator>
    bool operator<=(const set <Key, Compare, Allocator>& x,
    const set <Key, Compare, Allocator>& y);

Returns `!(y < x)`.

    template <class Key, class Compare, class Allocator>
    bool operator>=(const set <Key, Compare, Allocator>& x,
    const set <Key, Compare, Allocator>& y);

Returns `!(x < y)`.

### Specialized Algorithms

    template <class Key, class Compare, class Allocator>
    void swap(set <Key, Compare, Allocator>& a,
    set <Key, Compare, Allocator>& b);

Swaps the contents of `a` and `b`.

### Example

    //
    // setex.cpp
    //
    #include <set>
    #include <iostream>
     using namespace std;

    typedef set<double, less<double>, allocator<double> >
            set_type;
    ostream& operator<<(ostream& out, const set_type& s)
     {
    copy(s.begin(), s.end(),
         ostream_iterator<set_type::value_type,char>(cout," "));
    return out;
     }

    int main(void)
     {
    // create a set of doubles
       set_type   sd;
       int         i;

    for(i = 0; i < 10; ++i) {
    // insert values
    sd.insert(i);
       }

    // print out the set
    cout << sd << endl << endl;

    // now let's erase half of the elements in the set
    int half = sd.size() >> 1;
    set_type::iterator sdi = sd.begin();
    advance(sdi,half);
    sd.erase(sd.begin(),sdi);
    // print it out again
    cout << sd << endl << endl;

    // Make another set and an empty result set
    set_type sd2, sdResult;
    for (i = 1; i < 9; i++)
      sd2.insert(i+5);
    cout << sd2 << endl;
    // Try a couple of set algorithms
    set_union(sd.begin(),sd.end(),sd2.begin(),sd2.end(),
              inserter(sdResult,sdResult.begin()));
    cout << "Union:" << endl << sdResult << endl;
    sdResult.erase(sdResult.begin(),sdResult.end());
    set_intersection(sd.begin(),sd.end(),
                     sd2.begin(),sd2.end(),
                     inserter(sdResult,sdResult.begin()));
    cout << "Intersection:" << endl << sdResult << endl;
    return 0;
     }

Program Output

    0 1 2 3 4 5 6 7 8 9

    5 6 7 8 9

    6 7 8 9 10 11 12 13
    Union:
    5 6 7 8 9 10 11 12 13
    Intersection:
    6 7 8 9

### Warnings

Member function templates are used in all containers included in the Standard Template Library. An example of this feature is the constructor for set `<Key, Compare, Allocator>` that takes two templatized iterators:

    template <class InputIterator>
    set (InputIterator, InputIterator,
    const Compare& = Compare(),
    const Allocator& = Allocator());

set also has an insert function of this type. These functions, when not restricted by compiler limitations, allow you to use any type of input iterator as arguments. For compilers that do not support this feature, substitute functions allow you to use an iterator obtained from the same type of container as the one you are constructing (or calling a member function on), or you can use a pointer to the type of element you have in the container.

For example, if your compiler does not support member function templates, you can construct a set in the following two ways:

    int intarray[10];
    set<int> first_set(intarray, intarray + 10);
    set<int> second_set(first_set.begin(),
    first_set.end());

but not this way:

    set<long> long_set(first_set.begin(),
    first_set.end());

since the `long_set` and `first_set` are not the same type.

Also, many compilers do not support default template arguments. If your compiler is one of these you always need to supply the `Compare` template argument and the `Allocator` template argument. For instance, you need to write:

`set<int, less<int>, allocator<int> >`

instead of:

`set<int>`

If your compiler does not support namespaces, then you do not need the using declaration for `std`.

### See Also

allocator, Bidirectional Iterators, Containers, lexicographical_compare

Copyright (c) 1998, Rogue Wave Software, Inc.
Send mail to report errors or comment on the documentation.
OEM Release, June 1998