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Standard C++ Library
Copyright 1996, Rogue Wave Software, Inc.
NAME
set - An associative container that supports unique keys. A set
supports bidirectional iterators.
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 provides 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 provide 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;
typename reference;
typename const_reference;
typename iterator;
typename const_iterator;
typename size_type;
typename difference_type;
typename reverse_iterator;
typename 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);
iterator erase (iterator);
size_type erase (const key_type&);
iterator 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 AND DESTRUCTORS
explicit
set(const Compare& comp = Compare(),
const Allocator& alloc = Allocator());
The default constructor. 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 alloc
for all storage management.
set(const set<Key, Compare, Allocator>& x);
Copy constructor. Creates a copy of x.
~set();
The destructor. Releases any allocated memory for self.
ASSIGNMENT OPERATOR
set<Key, Compare, Allocator>&
operator=(const set<Key, Compare, Allocator>& x);
Assignment operator. Self will share an implementation with x.
Returns a reference to self.
ALLOCATOR
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 will always return 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
will always return 1 or 0.
iterator
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.
iterator
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 may be done
right after position then it takes amortized constant time.
Otherwise it will take 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 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);
Equality operator. 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);
Inequality operator. 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 lexico-
graphically 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);
Efficiently swaps the contents of a and b.
EXAMPLE
//
// set.cpp
//
#include <set>
#include <iostream.h>
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;
}
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 provided by the
Standard C++ Library. An example of this feature is the
constructor for set <Key, Compare, Allocator> that takes two
templated 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, we provide substitute functions that 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 need to always 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>
SEE ALSO
allocator, bidirectional_iterator, Cont ainer,
lexicographical_compare
STANDARDS CONFORMANCE
ANSI X3J16/ISO WG21 Joint C++ Committee
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