Standard C++ Library
Copyright 1998, 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 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 tem-
plate 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. Oth-
erwise, the default function object in the template argu-
ment is used. The template argument defaults to less (<).
Uses the allocator Allocator() for all storage manage-
ment.
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 implementa-
tion 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 ele-
ment.
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 inser-
tion 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 posi-
tion. Returns an iterator pointing to the element follow-
ing 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 inser-
tion is done right after position, then it takes amor-
tized 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 ele-
ment, 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 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);
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, Allo-
cator> 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 func-
tions, 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 func-
tions allow you to use an iterator obtained from the same
type of container as the one you are constructing (or cal-
ling 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 func-
tion 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 argu-
ments. If your compiler is one of these you always need to
supply the Compare template argument and the Allocator tem-
plate 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