`set` Class

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08/17/2021

The C++ Standard Library container class set is used to store and retrieve data from a collection. The values of the elements in the set are unique and serve as the key values according to which the data is automatically ordered. The value of an element in a set may not be changed directly. Instead, you must delete old values and insert elements with new values.

Syntax

template <class Key,
    class Traits=less<Key>,
    class Allocator=allocator<Key>>
class set

Parameters

Key
The element data type to be stored in the set.

Traits
The type that provides a function object that can compare two element values as sort keys to determine their relative order in the set. This argument is optional, and the binary predicate less <Key> is the default value.

In C++14, you can enable heterogeneous lookup by specifying the std::less<> or std::greater<> predicate that has no type parameters. See Heterogeneous Lookup in Associative Containers for more information.

Allocator
The type that represents the stored allocator object that encapsulates details about the set's allocation and deallocation of memory. This argument is optional, and the default value is allocator<Key>.

Remarks

A C++ Standard Library set is:

An associative container, which a variable size container that supports the efficient retrieval of element values based on an associated key value. Also, it's a simple associative container because its element values are its key values.
Reversible, because it provides a bidirectional iterator to access its elements.
Sorted, because its elements are ordered by key values within the container in accordance with a specified comparison function.
Unique in the sense that each of its elements must have a unique key. Since set is also a simple associative container, its elements are also unique.

A set is also described as a class template because the functionality it provides is generic and independent of the specific type of data contained as elements. The data type to be used is, instead, specified as a parameter in the class template along with the comparison function and allocator.

The choice of container type should be based in general on the type of searching and inserting required by the application. Associative containers are optimized for the operations of lookup, insertion, and removal. The member functions that explicitly support these operations are efficient, doing them in a time that is on average proportional to the logarithm of the number of elements in the container. Inserting elements invalidates no iterators, and removing elements invalidates only those iterators that pointed at the removed elements.

The set should be the associative container of choice when the conditions associating the values with their keys are satisfied by the application. The elements of a set are unique and serve as their own sort keys. A model for this type of structure is an ordered list of, say, words in which the words may occur only once. If multiple occurrences of the words were allowed, then a multiset would be the appropriate container structure. If values need to be attached to a list of unique key words, then a map would be an appropriate structure to contain this data. If instead the keys aren't unique, then a multimap would be the container of choice.

The set orders the sequence it controls by calling a stored function object of type key_compare. This stored object is a comparison function that may be accessed by calling the member function key_comp. In general, the elements need to be merely less than comparable to establish this order so that, given any two elements, it may be determined either that they're equivalent (in the sense that neither is less than the other) or that one is less than the other. This results in an ordering between the nonequivalent elements. On a more technical note, the comparison function is a binary predicate that induces a strict weak ordering in the standard mathematical sense. A binary predicate f(x,y) is a function object that has two argument objects x and y and a return value of true or false. An ordering imposed on a set is a strict weak ordering if the binary predicate is irreflexive, antisymmetric, and transitive and if equivalence is transitive, where two objects x and y are defined to be equivalent when both f x,y) and f(y,x) are false. If the stronger condition of equality between keys replaces that of equivalence, then the ordering becomes total (in the sense that all the elements are ordered with respect to each other) and the keys matched will be indiscernible from each other.

The iterator provided by the set class is a bidirectional iterator, but the class member functions insert and set have versions that take as template parameters a weaker input iterator, whose functionality requirements are more minimal than those guaranteed by the class of bidirectional iterators. The different iterator concepts form a family related by refinements in their functionality. Each iterator concept has its own set of requirements, and the algorithms that work with them must limit their assumptions to the requirements provided by that type of iterator. It may be assumed that an input iterator may be dereferenced to refer to some object and that it may be incremented to the next iterator in the sequence. This is a minimal set of functionality, but it's enough to be able to talk meaningfully about a range of iterators [ First, Last) in the context of the class's member functions.

Constructors

Name	Description
`set`	Constructs a set that is empty or that is a copy of all or part of some other set.

Typedefs

Name	Description
`allocator_type`	A type that represents the `allocator` class for the set object.
`const_iterator`	A type that provides a bidirectional iterator that can read a `const` element in the set.
`const_pointer`	A type that provides a pointer to a `const` element in a set.
`const_reference`	A type that provides a reference to a `const` element stored in a set for reading and doing `const` operations.
`const_reverse_iterator`	A type that provides a bidirectional iterator that can read any `const` element in the set.
`difference_type`	A signed integer type that can be used to represent the number of elements of a set in a range between elements pointed to by iterators.
`iterator`	A type that provides a bidirectional iterator that can read or modify any element in a set.
`key_compare`	A type that provides a function object that can compare two sort keys to determine the relative order of two elements in the set.
`key_type`	The type describes an object stored as an element of a set in its capacity as sort key.
`pointer`	A type that provides a pointer to an element in a set.
`reference`	A type that provides a reference to an element stored in a set.
`reverse_iterator`	A type that provides a bidirectional iterator that can read or modify an element in a reversed set.
`size_type`	An unsigned integer type that can represent the number of elements in a set.
`value_compare`	The type that provides a function object that can compare two elements to determine their relative order in the set.
`value_type`	The type describes an object stored as an element of a set in its capacity as a value.

Functions

Name	Description
`begin`	Returns an iterator that addresses the first element in the `set`.
`cbegin`	Returns a const iterator that addresses the first element in the `set`.
`cend`	Returns a const iterator that addresses the location succeeding the last element in a `set`.
`clear`	Erases all the elements of a `set`.
`contains`^C++20	Check if there's an element with the specified key in the `set`.
`count`	Returns the number of elements in a `set` whose key matches a parameter-specified key.
`crbegin`	Returns a const iterator addressing the first element in a reversed `set`.
`crend`	Returns a const iterator that addresses the location succeeding the last element in a reversed `set`.
`emplace`	Inserts an element constructed in place into a `set`.
`emplace_hint`	Inserts an element constructed in place into a `set`, with a placement hint.
`empty`	Tests if a `set` is empty.
`end`	Returns an iterator that addresses the location succeeding the last element in a `set`.
`equal_range`	Returns a pair of iterators respectively to the first element in a `set` with a key that is greater than a specified key and to the first element in the `set` with a key that is equal to or greater than the key.
`erase`	Removes an element or a range of elements in a set from specified positions or removes elements that match a specified key.
`find`	Returns an iterator addressing the location of an element in a `set` that has a key equivalent to a specified key.
`get_allocator`	Returns a copy of the `allocator` object used to construct the `set`.
`insert`	Inserts an element or a range of elements into a `set`.
`key_comp`	Retrieves a copy of the comparison object used to order keys in a `set`.
`lower_bound`	Returns an iterator to the first element in a set with a key that is equal to or greater than a specified key.
`max_size`	Returns the maximum length of the `set`.
`rbegin`	Returns an iterator addressing the first element in a reversed `set`.
`rend`	Returns an iterator that addresses the location succeeding the last element in a reversed `set`.
`size`	Returns the number of elements in the `set`.
`swap`	Exchanges the elements of two `set`s.
`upper_bound`	Returns an iterator to the first element in a `set` with a key that is greater than a specified key.
`value_comp`	Retrieves a copy of the comparison object used to order element values in a `set`.

Operators

Name	Description
`operator=`	Replaces the elements of a set with a copy of another set.

`allocator_type`

A type that represents the allocator class for the set object.

typedef Allocator allocator_type;

Remarks

allocator_type is a synonym for the template parameter Allocator.

Returns the function object that a multiset uses to order its elements, which is the template parameter Allocator.

For more information on Allocator, see the Remarks section of the set Class topic.

Example

See the example for get_allocator for an example that uses allocator_type.

`begin`

Returns an iterator that addresses the first element in the set.

const_iterator begin() const;

iterator begin();

Return Value

A bidirectional iterator addressing the first element in the set or the location succeeding an empty set.

Remarks

If the return value of begin is assigned to a const_iterator, the elements in the set object can't be modified. If the return value of begin is assigned to an iterator, the elements in the set object can be modified.

Example

// set_begin.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1;
   set <int>::iterator s1_Iter;
   set <int>::const_iterator s1_cIter;

   s1.insert( 1 );
   s1.insert( 2 );
   s1.insert( 3 );

   s1_Iter = s1.begin( );
   cout << "The first element of s1 is " << *s1_Iter << endl;

   s1_Iter = s1.begin( );
   s1.erase( s1_Iter );

   // The following 2 lines would err because the iterator is const
   // s1_cIter = s1.begin( );
   // s1.erase( s1_cIter );

   s1_cIter = s1.begin( );
   cout << "The first element of s1 is now " << *s1_cIter << endl;
}

The first element of s1 is 1
The first element of s1 is now 2

`cbegin`

Returns a const iterator that addresses the first element in the range.

const_iterator cbegin() const;

Return Value

A const bidirectional-access iterator that points at the first element of the range, or the location just beyond the end of an empty range (for an empty range, cbegin() == cend()).

Remarks

With the return value of cbegin, the elements in the range can't be modified.

You can use this member function in place of the begin() member function to guarantee that the return value is const_iterator. Typically, it's used in conjunction with the auto type deduction keyword, as shown in the following example. In the example, consider Container to be a modifiable (non- const) container of any kind that supports begin() and cbegin().

auto i1 = Container.begin();
// i1 is Container<T>::iterator
auto i2 = Container.cbegin();

// i2 is Container<T>::const_iterator

`cend`

Returns a const iterator that addresses the location just beyond the last element in a range.

const_iterator cend() const;

Return Value

A const bidirectional-access iterator that points just beyond the end of the range.

Remarks

cend is used to test whether an iterator has passed the end of its range.

You can use this member function in place of the end() member function to guarantee that the return value is const_iterator. Typically, it's used in conjunction with the auto type deduction keyword, as shown in the following example. In the example, consider Container to be a modifiable (non- const) container of any kind that supports end() and cend().

auto i1 = Container.end();
// i1 is Container<T>::iterator
auto i2 = Container.cend();

// i2 is Container<T>::const_iterator

The value returned by cend shouldn't be dereferenced.

`clear`

Erases all the elements of a set.

void clear();

Example

// set_clear.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1;

   s1.insert( 1 );
   s1.insert( 2 );

   cout << "The size of the set is initially " << s1.size( )
        << "." << endl;

   s1.clear( );
   cout << "The size of the set after clearing is "
        << s1.size( ) << "." << endl;
}

The size of the set is initially 2.
The size of the set after clearing is 0.

`const_iterator`

A type that provides a bidirectional iterator that can read a const element in the set.

typedef implementation-defined const_iterator;

Remarks

A type const_iterator can't be used to modify the value of an element.

Example

See the example for begin for an example that uses const_iterator.

`const_pointer`

A type that provides a pointer to a const element in a set.

typedef typename allocator_type::const_pointer const_pointer;

Remarks

A type const_pointer can't be used to modify the value of an element.

In most cases, a const_iterator should be used to access the elements in a const set object.

`const_reference`

A type that provides a reference to a const element stored in a set for reading and doing const operations.

typedef typename allocator_type::const_reference const_reference;

Example

// set_const_ref.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1;

   s1.insert( 10 );
   s1.insert( 20 );

   // Declare and initialize a const_reference &Ref1
   // to the 1st element
   const int &Ref1 = *s1.begin( );

   cout << "The first element in the set is "
        << Ref1 << "." << endl;

   // The following line would cause an error because the
   // const_reference can't be used to modify the set
   // Ref1 = Ref1 + 5;
}

The first element in the set is 10.

`const_reverse_iterator`

A type that provides a bidirectional iterator that can read any const element in the set.

typedef std::reverse_iterator<const_iterator> const_reverse_iterator;

Remarks

A type const_reverse_iterator can't modify the value of an element and is used to iterate through the set in reverse.

Example

See the example for rend for an example of how to declare and use the const_reverse_iterator.

`contains`

Check if there's an element with the specified key in the set.

bool contains(const Key& key) const;
template<class K> bool contains(const K& key) const;

Parameters

K
The type of the key.

key
The element's key value to look for.

Return Value

true if the element is found in the set; false otherwise.

Remarks

contains() is new in C++20. To use it, specify the /std:c++20 or later compiler option.

template<class K> bool contains(const K& key) const only participates in overload resolution if key_compare is transparent. See Heterogeneous lookup in associative containers for more information.

Example

// Requires /std:c++20 or /std:c++latest
#include <set>
#include <iostream>

int main()
{
    std::set<int> theSet = {1, 2};

    std::cout << std::boolalpha; // so booleans show as 'true' or 'false'
    std::cout << theSet.contains(2) << '\n';
    std::cout << theSet.contains(3) << '\n';

    return 0;
}

true
false

`count`

Returns the number of elements in a set whose key matches a parameter-specified key.

size_type count(const Key& key) const;

Parameters

key
The key of the elements to be matched from the set.

Return Value

1 if the set contains an element whose sort key matches the parameter key. 0 if the set doesn't contain an element with a matching key.

Remarks

The member function returns the number of elements in the following range:

[ lower_bound(key), upper_bound(key) ).

Example

The following example demonstrates the use of the set::count member function.

// set_count.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main()
{
    using namespace std;
    set<int> s1;
    set<int>::size_type i;

    s1.insert(1);
    s1.insert(1);

    // Keys must be unique in set, so duplicates are ignored
    i = s1.count(1);
    cout << "The number of elements in s1 with a sort key of 1 is: "
         << i << "." << endl;

    i = s1.count(2);
    cout << "The number of elements in s1 with a sort key of 2 is: "
         << i << "." << endl;
}

The number of elements in s1 with a sort key of 1 is: 1.
The number of elements in s1 with a sort key of 2 is: 0.

`crbegin`

Returns a const iterator addressing the first element in a reversed set.

const_reverse_iterator crbegin() const;

Return Value

A const reverse bidirectional iterator addressing the first element in a reversed set or addressing what had been the last element in the unreversed set.

Remarks

crbegin is used with a reversed set just as begin is used with a set.

With the return value of crbegin, the set object can't be modified.

Example

// set_crbegin.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1;
   set <int>::const_reverse_iterator s1_crIter;

   s1.insert( 10 );
   s1.insert( 20 );
   s1.insert( 30 );

   s1_crIter = s1.crbegin( );
   cout << "The first element in the reversed set is "
        << *s1_crIter << "." << endl;
}

The first element in the reversed set is 30.

`crend`

Returns a const iterator that addresses the location succeeding the last element in a reversed set.

const_reverse_iterator crend() const;

Return Value

A const reverse bidirectional iterator that addresses the location succeeding the last element in a reversed set (the location that had preceded the first element in the unreversed set).

Remarks

crend is used with a reversed set just as end is used with a set.

With the return value of crend, the set object can't be modified. The value returned by crend shouldn't be dereferenced.

crend can be used to test to whether a reverse iterator has reached the end of its set.

Example

// set_crend.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main() {
   using namespace std;
   set <int> s1;
   set <int>::const_reverse_iterator s1_crIter;

   s1.insert( 10 );
   s1.insert( 20 );
   s1.insert( 30 );

   s1_crIter = s1.crend( );
   s1_crIter--;
   cout << "The last element in the reversed set is "
        << *s1_crIter << "." << endl;
}

`difference_type`

A signed integer type that can be used to represent the number of elements of a set in a range between elements pointed to by iterators.

typedef typename allocator_type::difference_type difference_type;

Remarks

The difference_type is the type returned when subtracting or incrementing through iterators of the container. The difference_type is typically used to represent the number of elements in the range [ first, last) between the iterators first and last, includes the element pointed to by first and the range of elements up to, but not including, the element pointed to by last.

Although difference_type is available for all iterators that satisfy the requirements of an input iterator, which includes the class of bidirectional iterators supported by reversible containers such as set, subtraction between iterators is only supported by random-access iterators provided by a random-access container such as vector.

Example

// set_diff_type.cpp
// compile with: /EHsc
#include <iostream>
#include <set>
#include <algorithm>

int main( )
{
   using namespace std;

   set <int> s1;
   set <int>::iterator s1_Iter, s1_bIter, s1_eIter;

   s1.insert( 20 );
   s1.insert( 10 );
   s1.insert( 20 );   // won't insert as set elements are unique

   s1_bIter = s1.begin( );
   s1_eIter = s1.end( );

   set <int>::difference_type   df_typ5, df_typ10, df_typ20;

   df_typ5 = count( s1_bIter, s1_eIter, 5 );
   df_typ10 = count( s1_bIter, s1_eIter, 10 );
   df_typ20 = count( s1_bIter, s1_eIter, 20 );

   // the keys, and hence the elements of a set are unique,
   // so there's at most one of a given value
   cout << "The number '5' occurs " << df_typ5
        << " times in set s1.\n";
   cout << "The number '10' occurs " << df_typ10
        << " times in set s1.\n";
   cout << "The number '20' occurs " << df_typ20
        << " times in set s1.\n";

   // count the number of elements in a set
   set <int>::difference_type  df_count = 0;
   s1_Iter = s1.begin( );
   while ( s1_Iter != s1_eIter)
   {
      df_count++;
      s1_Iter++;
   }

   cout << "The number of elements in the set s1 is: "
        << df_count << "." << endl;
}

The number '5' occurs 0 times in set s1.
The number '10' occurs 1 times in set s1.
The number '20' occurs 1 times in set s1.
The number of elements in the set s1 is: 2.

`emplace`

Inserts an element constructed in place (no copy or move operations are performed).

template <class... Args>
pair<iterator, bool>
emplace(
    Args&&... args);

Parameters

args
The arguments forwarded to construct an element to be inserted into the set unless it already contains an element whose value is equivalently ordered.

Return Value

A pair whose bool component returns true if an insertion was made, and false if the map already contained an element whose value had an equivalent value in the ordering. The iterator component of the return value pair returns the address where a new element was inserted (if the bool component is true) or where the element was already located (if the bool component is false).

Remarks

No iterators or references are invalidated by this function.

During emplacement, if an exception is thrown, the container's state isn't modified.

Example

// set_emplace.cpp
// compile with: /EHsc
#include <set>
#include <string>
#include <iostream>

using namespace std;

template <typename S> void print(const S& s) {
    cout << s.size() << " elements: ";

    for (const auto& p : s) {
        cout << "(" << p << ") ";
    }

    cout << endl;
}

int main()
{
    set<string> s1;

    auto ret = s1.emplace("ten");

    if (!ret.second){
        cout << "Emplace failed, element with value \"ten\" already exists."
            << endl << "  The existing element is (" << *ret.first << ")"
            << endl;
        cout << "set not modified" << endl;
    }
    else{
        cout << "set modified, now contains ";
        print(s1);
    }
    cout << endl;

    ret = s1.emplace("ten");

    if (!ret.second){
        cout << "Emplace failed, element with value \"ten\" already exists."
            << endl << "  The existing element is (" << *ret.first << ")"
            << endl;
    }
    else{
        cout << "set modified, now contains ";
        print(s1);
    }
    cout << endl;
}

`emplace_hint`

Inserts an element constructed in place (no copy or move operations are performed), with a placement hint.

template <class... Args>
iterator emplace_hint(
    const_iterator where,
    Args&&... args);

Parameters

args
The arguments forwarded to construct an element to be inserted into the set unless the set already contains that element or, more generally, unless it already contains an element whose value is equivalently ordered.

where
The place to start searching for the correct point of insertion. (If that point immediately precedes where, insertion can occur in amortized constant time instead of logarithmic time.)

Return Value

An iterator to the newly inserted element.

If the insertion failed because the element already exists, returns an iterator to the existing element.

Remarks

No iterators or references are invalidated by this function.

During emplacement, if an exception is thrown, the container's state isn't modified.

Example

// set_emplace.cpp
// compile with: /EHsc
#include <set>
#include <string>
#include <iostream>

using namespace std;

template <typename S> void print(const S& s) {
    cout << s.size() << " elements: " << endl;

    for (const auto& p : s) {
        cout << "(" << p <<  ") ";
    }

    cout << endl;
}

int main()
{
    set<string> s1;

    // Emplace some test data
    s1.emplace("Anna");
    s1.emplace("Bob");
    s1.emplace("Carmine");

    cout << "set starting data: ";
    print(s1);
    cout << endl;

    // Emplace with hint
    // s1.end() should be the "next" element after this emplacement
    s1.emplace_hint(s1.end(), "Doug");

    cout << "set modified, now contains ";
    print(s1);
    cout << endl;
}

`empty`

Tests if a set is empty.

bool empty() const;

Return Value

true if the set is empty; false if the set is nonempty.

Example

// set_empty.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1, s2;
   s1.insert ( 1 );

   if ( s1.empty( ) )
      cout << "The set s1 is empty." << endl;
   else
      cout << "The set s1 is not empty." << endl;

   if ( s2.empty( ) )
      cout << "The set s2 is empty." << endl;
   else
      cout << "The set s2 is not empty." << endl;
}

The set s1 is not empty.
The set s2 is empty.

`end`

Returns the past-the-end iterator.

const_iterator end() const;

iterator end();

Return Value

The past-the-end iterator. If the set is empty, then set::end() == set::begin().

Remarks

end is used to test whether an iterator has passed the end of its set.

The value returned by end shouldn't be dereferenced.

For a code example, see set::find.

`equal_range`

Returns a pair of iterators respectively to the first element in a set with a key that is greater than or equal to a specified key and to the first element in the set with a key that is greater than the key.

pair <const_iterator, const_iterator> equal_range (const Key& key) const;

pair <iterator, iterator> equal_range (const Key& key);

Parameters

key
The argument key to be compared with the sort key of an element from the set being searched.

Return Value

A pair of iterators where the first is the lower_bound of the key and the second is the upper_bound of the key.

To access the first iterator of a pair pr returned by the member function, use pr. first, and to dereference the lower bound iterator, use *( pr. first). To access the second iterator of a pair pr returned by the member function, use pr. second, and to dereference the upper bound iterator, use *( pr. second).

Example

// set_equal_range.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   typedef set<int, less< int > > IntSet;
   IntSet s1;
   set <int, less< int > > :: const_iterator s1_RcIter;

   s1.insert( 10 );
   s1.insert( 20 );
   s1.insert( 30 );

   pair <IntSet::const_iterator, IntSet::const_iterator> p1, p2;
   p1 = s1.equal_range( 20 );

   cout << "The upper bound of the element with "
        << "a key of 20 in the set s1 is: "
        << *(p1.second) << "." << endl;

   cout << "The lower bound of the element with "
        << "a key of 20 in the set s1 is: "
        << *(p1.first) << "." << endl;

   // Compare the upper_bound called directly
   s1_RcIter = s1.upper_bound( 20 );
   cout << "A direct call of upper_bound( 20 ) gives "
        << *s1_RcIter << "," << endl
        << "matching the 2nd element of the pair"
        << " returned by equal_range( 20 )." << endl;

   p2 = s1.equal_range( 40 );

   // If no match is found for the key,
   // both elements of the pair return end( )
   if ( ( p2.first == s1.end( ) ) && ( p2.second == s1.end( ) ) )
      cout << "The set s1 doesn't have an element "
           << "with a key less than 40." << endl;
   else
      cout << "The element of set s1 with a key >= 40 is: "
           << *(p1.first) << "." << endl;
}

The upper bound of the element with a key of 20 in the set s1 is: 30.
The lower bound of the element with a key of 20 in the set s1 is: 20.
A direct call of upper_bound( 20 ) gives 30,
matching the 2nd element of the pair returned by equal_range( 20 ).
The set s1 doesn't have an element with a key less than 40.

`erase`

Removes an element or a range of elements in a set from specified positions or removes elements that match a specified key.

iterator erase(
    const_iterator Where);

iterator erase(
    const_iterator First,
    const_iterator Last);

size_type erase(
    const key_type& Key);

Parameters

Where
Position of the element to be removed.

First
Position of the first element to be removed.

Last
Position just beyond the last element to be removed.

Key
The key value of the elements to be removed.

Return Value

For the first two member functions, a bidirectional iterator that designates the first element remaining beyond any elements removed, or an element that is the end of the set if no such element exists.

For the third member function, returns the number of elements that have been removed from the set.

Example

// set_erase.cpp
// compile with: /EHsc
#include <set>
#include <string>
#include <iostream>
#include <iterator> // next() and prev() helper functions

using namespace std;

using myset = set<string>;

void printset(const myset& s) {
    for (const auto& iter : s) {
        cout << " [" << iter << "]";
    }
    cout << endl << "size() == " << s.size() << endl << endl;
}

int main()
{
    myset s1;

    // Fill in some data to test with, one at a time
    s1.insert("Bob");
    s1.insert("Robert");
    s1.insert("Bert");
    s1.insert("Rob");
    s1.insert("Bobby");

    cout << "Starting data of set s1 is:" << endl;
    printset(s1);
    // The 1st member function removes an element at a given position
    s1.erase(next(s1.begin()));
    cout << "After the 2nd element is deleted, the set s1 is:" << endl;
    printset(s1);

    // Fill in some data to test with, one at a time, using an initializer list
    myset s2{ "meow", "hiss", "purr", "growl", "yowl" };

    cout << "Starting data of set s2 is:" << endl;
    printset(s2);
    // The 2nd member function removes elements
    // in the range [First, Last)
    s2.erase(next(s2.begin()), prev(s2.end()));
    cout << "After the middle elements are deleted, the set s2 is:" << endl;
    printset(s2);

    myset s3;

    // Fill in some data to test with, one at a time, using emplace
    s3.emplace("C");
    s3.emplace("C#");
    s3.emplace("D");
    s3.emplace("D#");
    s3.emplace("E");
    s3.emplace("E#");
    s3.emplace("F");
    s3.emplace("F#");
    s3.emplace("G");
    s3.emplace("G#");
    s3.emplace("A");
    s3.emplace("A#");
    s3.emplace("B");

    cout << "Starting data of set s3 is:" << endl;
    printset(s3);
    // The 3rd member function removes elements with a given Key
    myset::size_type count = s3.erase("E#");
    // The 3rd member function also returns the number of elements removed
    cout << "The number of elements removed from s3 is: " << count << "." << endl;
    cout << "After the element with a key of \"E#\" is deleted, the set s3 is:" << endl;
    printset(s3);
}

`find`

Returns an iterator that refers to the location of an element in a set that has a key equivalent to a specified key.

iterator find(const Key& key);

const_iterator find(const Key& key) const;

Parameters

key
The key value to be matched by the sort key of an element from the set being searched.

Return Value

An iterator that refers to the location of an element with a specified key, or the location succeeding the last element in the set (set::end()) if no match is found for the key.

Remarks

The member function returns an iterator that refers to an element in the set whose key is equivalent to the argument key under a binary predicate that induces an ordering based on a less than comparability relation.

If the return value of find is assigned to a const_iterator, the set object can't be modified. If the return value of find is assigned to an iterator, the set object can be modified

Example

// compile with: /EHsc /W4 /MTd
#include <set>
#include <iostream>
#include <vector>
#include <string>

using namespace std;

template <typename T> void print_elem(const T& t) {
    cout << "(" << t << ") ";
}

template <typename T> void print_collection(const T& t) {
    cout << t.size() << " elements: ";

    for (const auto& p : t) {
        print_elem(p);
    }
    cout << endl;
}

template <typename C, class T> void findit(const C& c, T val) {
    cout << "Trying find() on value " << val << endl;
    auto result = c.find(val);
    if (result != c.end()) {
        cout << "Element found: "; print_elem(*result); cout << endl;
    } else {
        cout << "Element not found." << endl;
    }
}

int main()
{
    set<int> s1({ 40, 45 });
    cout << "The starting set s1 is: " << endl;
    print_collection(s1);

    vector<int> v;
    v.push_back(43);
    v.push_back(41);
    v.push_back(46);
    v.push_back(42);
    v.push_back(44);
    v.push_back(44); // attempt a duplicate

    cout << "Inserting the following vector data into s1: " << endl;
    print_collection(v);

    s1.insert(v.begin(), v.end());

    cout << "The modified set s1 is: " << endl;
    print_collection(s1);
    cout << endl;
    findit(s1, 45);
    findit(s1, 6);
}

`get_allocator`

Returns a copy of the allocator object used to construct the set.

allocator_type get_allocator() const;

Return Value

The allocator used by the set to manage memory, which is the template parameter Allocator.

For more information on Allocator, see the Remarks section of the set Class topic.

Remarks

Allocators for the set class specify how the class manages storage. The default allocators supplied with C++ Standard Library container classes is sufficient for most programming needs. Writing and using your own allocator class is an advanced C++ topic.

Example

// set_get_allocator.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int>::allocator_type s1_Alloc;
   set <int>::allocator_type s2_Alloc;
   set <double>::allocator_type s3_Alloc;
   set <int>::allocator_type s4_Alloc;

   // The following lines declare objects
   // that use the default allocator.
   set <int> s1;
   set <int, allocator<int> > s2;
   set <double, allocator<double> > s3;

   s1_Alloc = s1.get_allocator( );
   s2_Alloc = s2.get_allocator( );
   s3_Alloc = s3.get_allocator( );

   cout << "The number of integers that can be allocated"
        << endl << "before free memory is exhausted: "
        << s2.max_size( ) << "." << endl;

   cout << "\nThe number of doubles that can be allocated"
        << endl << "before free memory is exhausted: "
        << s3.max_size( ) <<  "." << endl;

   // The following line creates a set s4
   // with the allocator of multiset s1.
   set <int> s4( less<int>( ), s1_Alloc );

   s4_Alloc = s4.get_allocator( );

   // Two allocators are interchangeable if
   // storage allocated from each can be
   // deallocated by the other
   if( s1_Alloc == s4_Alloc )
   {
      cout << "\nThe allocators are interchangeable."
           << endl;
   }
   else
   {
      cout << "\nThe allocators are not interchangeable."
           << endl;
   }
}

insert

Inserts an element or a range of elements into a set.

// (1) single element
pair<iterator, bool> insert(
    const value_type& Val);

// (2) single element, perfect forwarded
template <class ValTy>
pair<iterator, bool>
insert(
    ValTy&& Val);

// (3) single element with hint
iterator insert(
    const_iterator Where,
    const value_type& Val);

// (4) single element, perfect forwarded, with hint
template <class ValTy>
iterator insert(
    const_iterator Where,
    ValTy&& Val);

// (5) range
template <class InputIterator>
void insert(
    InputIterator First,
    InputIterator Last);

// (6) initializer list
void insert(
    initializer_list<value_type>
IList);

Parameters

Val
The value of an element to be inserted into the set unless it already contains an element whose value is equivalently ordered.

Where
The place to start searching for the correct point of insertion. (If that point immediately precedes Where, insertion can occur in amortized constant time instead of logarithmic time.)

ValTy
Template parameter that specifies the argument type that the set can use to construct an element of value_type, and perfect-forwards Val as an argument.

First
The position of the first element to be copied.

Last
The position just beyond the last element to be copied.

InputIterator
Template function argument that meets the requirements of an input iterator that points to elements of a type that can be used to construct value_type objects.

IList
The initializer_list from which to copy the elements.

Return Value

The single-element member functions, (1) and (2), return a pair whose bool component is true if an insertion was made, and false if the set already contained an element of equivalent value in the ordering. The iterator component of the return-value pair points to the newly inserted element if the bool component is true, or to the existing element if the bool component is false.

The single-element-with-hint member functions, (3) and (4), return an iterator that points to the position where the new element was inserted into the set or, if an element with an equivalent key already exists, to the existing element.

Remarks

No iterators, pointers, or references are invalidated by this function.

During the insertion of just one element, if an exception is thrown, the container's state isn't modified. During the insertion of multiple elements, if an exception is thrown, the container is left in an unspecified but valid state.

To access the iterator component of a pair pr that's returned by the single-element member functions, use pr.first; to dereference the iterator within the returned pair, use *pr.first, giving you an element. To access the bool component, use pr.second. For an example, see the sample code later in this article.

The value_type of a container is a typedef that belongs to the container, and, for set, set<V>::value_type is type const V.

The range member function (5) inserts the sequence of element values into a set that corresponds to each element addressed by an iterator in the range [First, Last); therefore, Last doesn't get inserted. The container member function end() refers to the position just after the last element in the container—for example, the statement s.insert(v.begin(), v.end()); attempts to insert all elements of v into s. Only elements that have unique values in the range are inserted; duplicates are ignored. To observe which elements are rejected, use the single-element versions of insert.

The initializer list member function (6) uses an initializer_list to copy elements into the set.

For insertion of an element constructed in place—that is, no copy or move operations are performed—see set::emplace and set::emplace_hint.

Example

// set_insert.cpp
// compile with: /EHsc
#include <set>
#include <iostream>
#include <string>
#include <vector>

using namespace std;

template <typename S> void print(const S& s) {
    cout << s.size() << " elements: ";

    for (const auto& p : s) {
        cout << "(" << p << ") ";
    }

    cout << endl;
}

int main()
{
    // insert single values
    set<int> s1;
    // call insert(const value_type&) version
    s1.insert({ 1, 10 });
    // call insert(ValTy&&) version
    s1.insert(20);

    cout << "The original set values of s1 are:" << endl;
    print(s1);

    // intentionally attempt a duplicate, single element
    auto ret = s1.insert(1);
    if (!ret.second){
        auto elem = *ret.first;
        cout << "Insert failed, element with value 1 already exists."
            << endl << "  The existing element is (" << elem << ")"
            << endl;
    }
    else{
        cout << "The modified set values of s1 are:" << endl;
        print(s1);
    }
    cout << endl;

    // single element, with hint
    s1.insert(s1.end(), 30);
    cout << "The modified set values of s1 are:" << endl;
    print(s1);
    cout << endl;

    // The templatized version inserting a jumbled range
    set<int> s2;
    vector<int> v;
    v.push_back(43);
    v.push_back(294);
    v.push_back(41);
    v.push_back(330);
    v.push_back(42);
    v.push_back(45);

    cout << "Inserting the following vector data into s2:" << endl;
    print(v);

    s2.insert(v.begin(), v.end());

    cout << "The modified set values of s2 are:" << endl;
    print(s2);
    cout << endl;

    // The templatized versions move-constructing elements
    set<string>  s3;
    string str1("blue"), str2("green");

    // single element
    s3.insert(move(str1));
    cout << "After the first move insertion, s3 contains:" << endl;
    print(s3);

    // single element with hint
    s3.insert(s3.end(), move(str2));
    cout << "After the second move insertion, s3 contains:" << endl;
    print(s3);
    cout << endl;

    set<int> s4;
    // Insert the elements from an initializer_list
    s4.insert({ 4, 44, 2, 22, 3, 33, 1, 11, 5, 55 });
    cout << "After initializer_list insertion, s4 contains:" << endl;
    print(s4);
    cout << endl;
}

`iterator`

A type that provides a constant bidirectional iterator that can read any element in a set.

typedef implementation-defined iterator;

Example

See the example for begin for an example of how to declare and use an iterator.

`key_comp`

Retrieves a copy of the comparison object used to order keys in a set.

key_compare key_comp() const;

Return Value

Returns the function object that a set uses to order its elements, which is the template parameter Traits.

For more information on Traits, see the set Class topic.

Remarks

The stored object defines the member function:

bool operator()(const Key&_xVal, const Key&_yVal);

which returns true if _xVal precedes and isn't equal to _yVal in the sort order.

Both key_compare and value_compare are synonyms for the template parameter Traits. Both types are provided for the set and multiset classes, where they're identical, for compatibility with the map and multimap classes, where they're distinct.

Example

// set_key_comp.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;

   set <int, less<int> > s1;
   set<int, less<int> >::key_compare kc1 = s1.key_comp( ) ;
   bool result1 = kc1( 2, 3 ) ;
   if( result1 == true )
   {
      cout << "kc1( 2,3 ) returns value of true, "
           << "where kc1 is the function object of s1."
           << endl;
   }
   else
   {
      cout << "kc1( 2,3 ) returns value of false "
           << "where kc1 is the function object of s1."
           << endl;
   }

   set <int, greater<int> > s2;
   set<int, greater<int> >::key_compare kc2 = s2.key_comp( ) ;
   bool result2 = kc2( 2, 3 ) ;
   if(result2 == true)
   {
      cout << "kc2( 2,3 ) returns value of true, "
           << "where kc2 is the function object of s2."
           << endl;
   }
   else
   {
      cout << "kc2( 2,3 ) returns value of false, "
           << "where kc2 is the function object of s2."
           << endl;
   }
}

kc1( 2,3 ) returns value of true, where kc1 is the function object of s1.
kc2( 2,3 ) returns value of false, where kc2 is the function object of s2.

`key_compare`

A type that provides a function object that can compare two sort keys to determine the relative order of two elements in the set.

typedef Traits key_compare;

Remarks

key_compare is a synonym for the template parameter Traits.

For more information on Traits, see the set Class topic.

Example

See the example for key_comp for an example of how to declare and use key_compare.

`key_type`

A type that describes an object stored as an element of a set in its capacity as sort key.

typedef Key key_type;

Remarks

key_type is a synonym for the template parameter Key.

For more information on Key, see the Remarks section of the set Class topic.

Both key_type and value_type are synonyms for the template parameter Key. Both types are provided for the set and multiset classes, where they're identical, for compatibility with the map and multimap classes, where they're distinct.

Example

See the example for value_type for an example of how to declare and use key_type.

`lower_bound`

Returns an iterator to the first element in a set with a key that is equal to or greater than a specified key.

const_iterator lower_bound(const Key& key) const;

iterator lower_bound(const Key& key);

Parameters

key
The argument key to be compared with the sort key of an element from the set being searched.

Return Value

An iterator or const_iterator that addresses the location of an element in a set that with a key that is equal to or greater than the argument key or that addresses the location succeeding the last element in the set if no match is found for the key.

Example

// set_lower_bound.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1;
   set <int> :: const_iterator s1_AcIter, s1_RcIter;

   s1.insert( 10 );
   s1.insert( 20 );
   s1.insert( 30 );

   s1_RcIter = s1.lower_bound( 20 );
   cout << "The element of set s1 with a key of 20 is: "
        << *s1_RcIter << "." << endl;

   s1_RcIter = s1.lower_bound( 40 );

   // If no match is found for the key, end( ) is returned
   if ( s1_RcIter == s1.end( ) )
      cout << "The set s1 doesn't have an element "
           << "with a key of 40." << endl;
   else
      cout << "The element of set s1 with a key of 40 is: "
           << *s1_RcIter << "." << endl;

   // The element at a specific location in the set can be found
   // by using a dereferenced iterator that addresses the location
   s1_AcIter = s1.end( );
   s1_AcIter--;
   s1_RcIter = s1.lower_bound( *s1_AcIter );
   cout << "The element of s1 with a key matching "
        << "that of the last element is: "
        << *s1_RcIter << "." << endl;
}

The element of set s1 with a key of 20 is: 20.
The set s1 doesn't have an element with a key of 40.
The element of s1 with a key matching that of the last element is: 30.

`max_size`

Returns the maximum length of the set.

size_type max_size() const;

Return Value

The maximum possible length of the set.

Example

// set_max_size.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1;
   set <int>::size_type i;

   i = s1.max_size( );
   cout << "The maximum possible length "
        << "of the set is " << i << "." << endl;
}

`operator=`

Replaces the elements of this set using elements from another set.

set& operator=(const set& right);

set& operator=(set&& right);

Parameters

right
The set providing new elements to be assigned to this set.

Remarks

The first version of operator= uses an lvalue reference for right, to copy elements from right to this set.

The second version uses an rvalue reference for right. It moves elements from right to this set.

Any elements in this set before the operator function executes are discarded.

Example

// set_operator_as.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
   {
   using namespace std;
   set<int> v1, v2, v3;
   set<int>::iterator iter;

   v1.insert(10);

   cout << "v1 = " ;
   for (iter = v1.begin(); iter != v1.end(); iter++)
      cout << *iter << " ";
   cout << endl;

   v2 = v1;
   cout << "v2 = ";
   for (iter = v2.begin(); iter != v2.end(); iter++)
      cout << *iter << " ";
   cout << endl;

// move v1 into v2
   v2.clear();
   v2 = move(v1);
   cout << "v2 = ";
   for (iter = v2.begin(); iter != v2.end(); iter++)
      cout << *iter << " ";
   cout << endl;
   }

`pointer`

A type that provides a pointer to an element in a set.

typedef typename allocator_type::pointer pointer;

Remarks

A type pointer can be used to modify the value of an element.

In most cases, an iterator should be used to access the elements in a set object.

`rbegin`

Returns an iterator addressing the first element in a reversed set.

const_reverse_iterator rbegin() const;

reverse_iterator rbegin();

Return Value

A reverse bidirectional iterator addressing the first element in a reversed set or addressing what had been the last element in the unreversed set.

Remarks

rbegin is used with a reversed set just as begin is used with a set.

If the return value of rbegin is assigned to a const_reverse_iterator, then the set object can't be modified. If the return value of rbegin is assigned to a reverse_iterator, then the set object can be modified.

rbegin can be used to iterate through a set backwards.

Example

// set_rbegin.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1;
   set <int>::iterator s1_Iter;
   set <int>::reverse_iterator s1_rIter;

   s1.insert( 10 );
   s1.insert( 20 );
   s1.insert( 30 );

   s1_rIter = s1.rbegin( );
   cout << "The first element in the reversed set is "
        << *s1_rIter << "." << endl;

   // begin can be used to start an iteration
   // through a set in a forward order
   cout << "The set is:";
   for ( s1_Iter = s1.begin( ) ; s1_Iter != s1.end( ); s1_Iter++ )
      cout << " " << *s1_Iter;
   cout << endl;

   // rbegin can be used to start an iteration
   // through a set in a reverse order
   cout << "The reversed set is:";
   for ( s1_rIter = s1.rbegin( ) ; s1_rIter != s1.rend( ); s1_rIter++ )
      cout << " " << *s1_rIter;
   cout << endl;

   // A set element can be erased by dereferencing to its key
   s1_rIter = s1.rbegin( );
   s1.erase ( *s1_rIter );

   s1_rIter = s1.rbegin( );
   cout << "After the erasure, the first element "
        << "in the reversed set is "<< *s1_rIter << "." << endl;
}

The first element in the reversed set is 30.
The set is: 10 20 30
The reversed set is: 30 20 10
After the erasure, the first element in the reversed set is 20.

`reference`

A type that provides a reference to an element stored in a set.

typedef typename allocator_type::reference reference;

Example

// set_reference.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1;

   s1.insert( 10 );
   s1.insert( 20 );

   // Declare and initialize a reference &Ref1 to the 1st element
   const int &Ref1 = *s1.begin( );

   cout << "The first element in the set is "
        << Ref1 << "." << endl;
}

The first element in the set is 10.

`rend`

Returns an iterator that addresses the location succeeding the last element in a reversed set.

const_reverse_iterator rend() const;

reverse_iterator rend();

Return Value

A reverse bidirectional iterator that addresses the location succeeding the last element in a reversed set (the location that had preceded the first element in the unreversed set).

Remarks

rend is used with a reversed set just as end is used with a set.

If the return value of rend is assigned to a const_reverse_iterator, then the set object can't be modified. If the return value of rend is assigned to a reverse_iterator, then the set object can be modified. The value returned by rend shouldn't be dereferenced.

rend can be used to test to whether a reverse iterator has reached the end of its set.

Example

// set_rend.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main() {
   using namespace std;
   set <int> s1;
   set <int>::iterator s1_Iter;
   set <int>::reverse_iterator s1_rIter;
   set <int>::const_reverse_iterator s1_crIter;

   s1.insert( 10 );
   s1.insert( 20 );
   s1.insert( 30 );

   s1_rIter = s1.rend( );
   s1_rIter--;
   cout << "The last element in the reversed set is "
        << *s1_rIter << "." << endl;

   // end can be used to terminate an iteration
   // through a set in a forward order
   cout << "The set is: ";
   for ( s1_Iter = s1.begin( ) ; s1_Iter != s1.end( ); s1_Iter++ )
      cout << *s1_Iter << " ";
   cout << "." << endl;

   // rend can be used to terminate an iteration
   // through a set in a reverse order
   cout << "The reversed set is: ";
   for ( s1_rIter = s1.rbegin( ) ; s1_rIter != s1.rend( ); s1_rIter++ )
      cout << *s1_rIter << " ";
   cout << "." << endl;

   s1_rIter = s1.rend( );
   s1_rIter--;
   s1.erase ( *s1_rIter );

   s1_rIter = s1.rend( );
   --s1_rIter;
   cout << "After the erasure, the last element in the "
        << "reversed set is " << *s1_rIter << "." << endl;
}

`reverse_iterator`

A type that provides a bidirectional iterator that can read or modify an element in a reversed set.

typedef std::reverse_iterator<iterator> reverse_iterator;

Remarks

A type reverse_iterator is used to iterate through the set in reverse.

Example

See the example for rbegin for an example of how to declare and use reverse_iterator.

`set`

Constructs a set that is empty or that is a copy of all or part of some other set.

set();

explicit set(
    const Traits& Comp);

set(
    const Traits& Comp,
    const Allocator& Al);

set(
    const set& Right);

set(
    set&& Right);

set(
    initializer_list<Type> IList);

set(
    initializer_list<Type> IList,
    const Compare& Comp);

set(
    initializer_list<Type> IList,
    const Compare& Comp,
    const Allocator& Al);

template <class InputIterator>
set(
    InputIterator First,
    InputIterator Last);

template <class InputIterator>
set(
    InputIterator First,
    InputIterator Last,
    const Traits& Comp);

template <class InputIterator>
set(
    InputIterator First,
    InputIterator Last,
    const Traits& Comp,
    const Allocator& Al);

Parameters

Al
The storage allocator class to be used for this set object, which defaults to Allocator.

Comp
The comparison function of type const Traits used to order the elements in the set, which defaults to Compare.

Rght
The set of which the constructed set is to be a copy.

First
The position of the first element in the range of elements to be copied.

Last
The position of the first element beyond the range of elements to be copied.

IList
The initializer_list from which to copy the elements.

Remarks

All constructors store a type of allocator object that manages memory storage for the set and that can later be returned by calling get_allocator. The allocator parameter is often omitted in the class declarations and preprocessing macros used to substitute alternative allocators.

All constructors initialize their sets.

All constructors store a function object of type Traits that is used to establish an order among the keys of the set and that can later be returned by calling key_comp.

The first three constructors specify an empty initial set, the second specifying the type of comparison function (comp) to be used in establishing the order of the elements and the third explicitly specifying the allocator type (al) to be used. The keyword explicit suppresses certain kinds of automatic type conversion.

The fourth constructor specifies a copy of the set right.

The next three constructors use an initializer_list to specify the elements.

The next three constructors copy the range [ first, last) of a set with increasing explicitness in specifying the type of comparison function of class Traits and Allocator.

The eighth constructor specifies a copy of the set by moving right.

Example

// set_set.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main()
{
    using namespace std;

    // Create an empty set s0 of key type integer
    set <int> s0;

    // Create an empty set s1 with the key comparison
    // function of less than, then insert 4 elements
    set <int, less<int> > s1;
    s1.insert(10);
    s1.insert(20);
    s1.insert(30);
    s1.insert(40);

    // Create an empty set s2 with the key comparison
    // function of less than, then insert 2 elements
    set <int, less<int> > s2;
    s2.insert(10);
    s2.insert(20);

    // Create a set s3 with the
    // allocator of set s1
    set <int>::allocator_type s1_Alloc;
    s1_Alloc = s1.get_allocator();
    set <int> s3(less<int>(), s1_Alloc);
    s3.insert(30);

    // Create a copy, set s4, of set s1
    set <int> s4(s1);

    // Create a set s5 by copying the range s1[ first,  last)
    set <int>::const_iterator s1_bcIter, s1_ecIter;
    s1_bcIter = s1.begin();
    s1_ecIter = s1.begin();
    s1_ecIter++;
    s1_ecIter++;
    set <int> s5(s1_bcIter, s1_ecIter);

    // Create a set s6 by copying the range s4[ first,  last)
    // and with the allocator of set s2
    set <int>::allocator_type s2_Alloc;
    s2_Alloc = s2.get_allocator();
    set <int> s6(s4.begin(), ++s4.begin(), less<int>(), s2_Alloc);

    cout << "s1 =";
    for (auto i : s1)
        cout << " " << i;
    cout << endl;

    cout << "s2 = " << *s2.begin() << " " << *++s2.begin() << endl;

    cout << "s3 =";
    for (auto i : s3)
        cout << " " << i;
    cout << endl;

    cout << "s4 =";
    for (auto i : s4)
        cout << " " << i;
    cout << endl;

    cout << "s5 =";
    for (auto i : s5)
        cout << " " << i;
    cout << endl;

    cout << "s6 =";
    for (auto i : s6)
        cout << " " << i;
    cout << endl;

    // Create a set by moving s5
    set<int> s7(move(s5));
    cout << "s7 =";
    for (auto i : s7)
        cout << " " << i;
    cout << endl;

    // Create a set with an initializer_list
    cout << "s8 =";
    set<int> s8{ { 1, 2, 3, 4 } };
    for (auto i : s8)
        cout << " " << i;
    cout << endl;

    cout << "s9 =";
    set<int> s9{ { 5, 6, 7, 8 }, less<int>() };
    for (auto i : s9)
        cout << " " << i;
    cout << endl;

    cout << "s10 =";
    set<int> s10{ { 10, 20, 30, 40 }, less<int>(), s9.get_allocator() };
    for (auto i : s10)
        cout << " " << i;
    cout << endl;
}

s1 = 10 20 30 40s2 = 10 20s3 = 30s4 = 10 20 30 40s5 = 10 20s6 = 10s7 = 10 20s8 = 1 2 3 4s9 = 5 6 7 8s10 = 10 20 30 40

`size`

Returns the number of elements in the set.

size_type size() const;

Return Value

The current length of the set.

Example

// set_size.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1;
   set <int> :: size_type i;

   s1.insert( 1 );
   i = s1.size( );
   cout << "The set length is " << i << "." << endl;

   s1.insert( 2 );
   i = s1.size( );
   cout << "The set length is now " << i << "." << endl;
}

The set length is 1.
The set length is now 2.

`size_type`

An unsigned integer type that can represent the number of elements in a set.

typedef typename allocator_type::size_type size_type;

Example

See the example for size for an example of how to declare and use size_type

`swap`

Exchanges the elements of two sets.

void swap(
    set<Key, Traits, Allocator>& right);

Parameters

right
The argument set providing the elements to be swapped with the target set.

Remarks

The member function invalidates no references, pointers, or iterators that designate elements in the two sets whose elements are being exchanged.

Example

// set_swap.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1, s2, s3;
   set <int>::iterator s1_Iter;

   s1.insert( 10 );
   s1.insert( 20 );
   s1.insert( 30 );
   s2.insert( 100 );
   s2.insert( 200 );
   s3.insert( 300 );

   cout << "The original set s1 is:";
   for ( s1_Iter = s1.begin( ); s1_Iter != s1.end( ); s1_Iter++ )
      cout << " " << *s1_Iter;
   cout   << "." << endl;

   // This is the member function version of swap
   s1.swap( s2 );

   cout << "After swapping with s2, list s1 is:";
   for ( s1_Iter = s1.begin( ); s1_Iter != s1.end( ); s1_Iter++ )
      cout << " " << *s1_Iter;
   cout  << "." << endl;

   // This is the specialized template version of swap
   swap( s1, s3 );

   cout << "After swapping with s3, list s1 is:";
   for ( s1_Iter = s1.begin( ); s1_Iter != s1.end( ); s1_Iter++ )
      cout << " " << *s1_Iter;
   cout   << "." << endl;
}

The original set s1 is: 10 20 30.
After swapping with s2, list s1 is: 100 200.
After swapping with s3, list s1 is: 300.

`upper_bound`

Returns an iterator to the first element in a set that with a key that is greater than a specified key.

const_iterator upper_bound(const Key& key) const;

iterator upper_bound(const Key& key);

Parameters

key
The argument key to be compared with the sort key of an element from the set being searched.

Return Value

An iterator or const_iterator that addresses the location of an element in a set that with a key that is greater than the argument key, or that addresses the location succeeding the last element in the set if no match is found for the key.

Example

// set_upper_bound.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1;
   set <int> :: const_iterator s1_AcIter, s1_RcIter;

   s1.insert( 10 );
   s1.insert( 20 );
   s1.insert( 30 );

   s1_RcIter = s1.upper_bound( 20 );
   cout << "The first element of set s1 with a key greater "
        << "than 20 is: " << *s1_RcIter << "." << endl;

   s1_RcIter = s1.upper_bound( 30 );

   // If no match is found for the key, end( ) is returned
   if ( s1_RcIter == s1.end( ) )
      cout << "The set s1 doesn't have an element "
           << "with a key greater than 30." << endl;
   else
      cout << "The element of set s1 with a key > 40 is: "
           << *s1_RcIter << "." << endl;

   // The element at a specific location in the set can be found
   // by using a dereferenced iterator addressing the location
   s1_AcIter = s1.begin( );
   s1_RcIter = s1.upper_bound( *s1_AcIter );
   cout << "The first element of s1 with a key greater than"
        << endl << "that of the initial element of s1 is: "
        << *s1_RcIter << "." << endl;
}

The first element of set s1 with a key greater than 20 is: 30.
The set s1 doesn't have an element with a key greater than 30.
The first element of s1 with a key greater than
that of the initial element of s1 is: 20.

`value_comp`

Retrieves a copy of the comparison object used to order element values in a set.

value_compare value_comp() const;

Return Value

Returns the function object that a set uses to order its elements, which is the template parameter Traits.

For more information on Traits, see the set Class topic.

Remarks

The stored object defines the member function:

bool operator(const Key&_xVal, const Key&_yVal);

which returns true if _xVal precedes and isn't equal to _yVal in the sort order.

Both value_compare and key_compare are synonyms for the template parameter Traits. Both types are provided for the set and multiset classes, where they're identical, for compatibility with the map and multimap classes, where they're distinct.

Example

// set_value_comp.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;

   set <int, less<int> > s1;
   set <int, less<int> >::value_compare vc1 = s1.value_comp( );
   bool result1 = vc1( 2, 3 );
   if( result1 == true )
   {
      cout << "vc1( 2,3 ) returns value of true, "
           << "where vc1 is the function object of s1."
           << endl;
   }
   else
   {
      cout << "vc1( 2,3 ) returns value of false, "
           << "where vc1 is the function object of s1."
           << endl;
   }

   set <int, greater<int> > s2;
   set<int, greater<int> >::value_compare vc2 = s2.value_comp( );
   bool result2 = vc2( 2, 3 );
   if( result2 == true )
   {
      cout << "vc2( 2,3 ) returns value of true, "
           << "where vc2 is the function object of s2."
           << endl;
   }
   else
   {
      cout << "vc2( 2,3 ) returns value of false, "
           << "where vc2 is the function object of s2."
           << endl;
   }
}

vc1( 2,3 ) returns value of true, where vc1 is the function object of s1.
vc2( 2,3 ) returns value of false, where vc2 is the function object of s2.

`value_compare`

A type that provides a function object that can compare two element values to determine their relative order in the set.

typedef key_compare value_compare;

Remarks

value_compare is a synonym for the template parameter Traits.

For more information on Traits, see the set Class topic.

Example

See the example for value_comp for an example of how to declare and use value_compare.

`value_type`

A type that describes an object stored as an element of a set in its capacity as a value.

typedef Key value_type;

Remarks

value_type is a synonym for the template parameter Key.

For more information on Key, see the Remarks section of the set Class topic.

Example

// set_value_type.cpp
// compile with: /EHsc
#include <set>
#include <iostream>

int main( )
{
   using namespace std;
   set <int> s1;
   set <int>::iterator s1_Iter;

   set <int>::value_type svt_Int;   // Declare value_type
   svt_Int = 10;            // Initialize value_type

   set <int> :: key_type skt_Int;   // Declare key_type
   skt_Int = 20;             // Initialize key_type

   s1.insert( svt_Int );         // Insert value into s1
   s1.insert( skt_Int );         // Insert key into s1

   // A set accepts key_types or value_types as elements
   cout << "The set has elements:";
   for ( s1_Iter = s1.begin( ) ; s1_Iter != s1.end( ); s1_Iter++)
      cout << " " << *s1_Iter;
   cout << "." << endl;
}

The set has elements: 10 20.

แชร์ผ่าน

set Class

Syntax

Parameters

Remarks

Constructors

Typedefs

Functions

Operators

allocator_type

Remarks

Example

begin

Return Value

Remarks

Example

cbegin

Return Value

Remarks

cend

Return Value

Remarks

clear

Example

const_iterator

Remarks

Example

const_pointer

Remarks

const_reference

Example

const_reverse_iterator

Remarks

Example

contains

Parameters

Return Value

Remarks

Example

count

Parameters

Return Value

Remarks

Example

crbegin

Return Value

Remarks

Example

crend

Return Value

Remarks

Example

difference_type

Remarks

Example

emplace

Parameters

Return Value

Remarks

Example

emplace_hint

Parameters

Return Value

Remarks

Example

empty

Return Value

Example

end

Return Value

Remarks

equal_range

Parameters

Return Value

Example

erase

Parameters

Return Value

Example

find

`set` Class

`allocator_type`

`begin`

`cbegin`

`cend`

`clear`

`const_iterator`

`const_pointer`

`const_reference`

`const_reverse_iterator`

`contains`

`count`

`crbegin`

`crend`

`difference_type`

`emplace`

`emplace_hint`

`empty`

`end`

`equal_range`

`erase`

`find`

`get_allocator`

`iterator`

`key_comp`

`key_compare`

`key_type`

`lower_bound`

`max_size`

`operator=`

`pointer`

`rbegin`

`reference`

`rend`

`reverse_iterator`

`set`

`size`

`size_type`

`swap`

`upper_bound`

`value_comp`