Category: containers | Component type: type |
Set and multiset are particularly well suited to the set algorithms includes, set_union, set_intersection, set_difference, and set_symmetric_difference. The reason for this is twofold. First, the set algorithms require their arguments to be sorted ranges, and, since set and multiset are Sorted Associative Containers, their elements are always sorted in ascending order. Second, the output range of these algorithms is always sorted, and inserting a sorted range into a set or multiset is a fast operation: the Unique Sorted Associative Container and Multiple Sorted Associative Container requirements guarantee that inserting a range takes only linear time if the range is already sorted.
Set has the important property that inserting a new element into a set does not invalidate iterators that point to existing elements. Erasing an element from a set also does not invalidate any iterators, except, of course, for iterators that actually point to the element that is being erased.
struct ltstr { bool operator()(const char* s1, const char* s2) const { return strcmp(s1, s2) < 0; } }; int main() { const int N = 6; const char* a[N] = {"isomer", "ephemeral", "prosaic", "nugatory", "artichoke", "serif"}; const char* b[N] = {"flat", "this", "artichoke", "frigate", "prosaic", "isomer"}; set<const char*, ltstr> A(a, a + N); set<const char*, ltstr> B(b, b + N); set<const char*, ltstr> C; cout << "Set A: "; copy(A.begin(), A.end(), ostream_iterator<const char*>(cout, " ")); cout << endl; cout << "Set B: "; copy(B.begin(), B.end(), ostream_iterator<const char*>(cout, " ")); cout << endl; cout << "Union: "; set_union(A.begin(), A.end(), B.begin(), B.end(), ostream_iterator<const char*>(cout, " "), ltstr()); cout << endl; cout << "Intersection: "; set_intersection(A.begin(), A.end(), B.begin(), B.end(), ostream_iterator<const char*>(cout, " "), ltstr()); cout << endl; set_difference(A.begin(), A.end(), B.begin(), B.end(), inserter(C, C.begin()), ltstr()); cout << "Set C (difference of A and B): "; copy(C.begin(), C.end(), ostream_iterator<const char*>(cout, " ")); cout << endl; }
Parameter | Description | Default |
---|---|---|
Key | The set's key type and value type. This is also defined as set::key_type and set::value_type | |
Compare | The key comparison function, a Strict Weak Ordering whose argument type is key_type; it returns true if its first argument is less than its second argument, and false otherwise. This is also defined as set::key_compare and set::value_compare. | less<Key> |
Alloc | The set's allocator, used for all internal memory management. | alloc |
Member | Where defined | Description |
---|---|---|
value_type | Container | The type of object, T, stored in the set. |
key_type | Associative Container | The key type associated with value_type. |
key_compare | Sorted Associative Container | Function object that compares two keys for ordering. |
value_compare | Sorted Associative Container | Function object that compares two values for ordering. |
pointer | Container | Pointer to T. |
reference | Container | Reference to T |
const_reference | Container | Const reference to T |
size_type | Container | An unsigned integral type. |
difference_type | Container | A signed integral type. |
iterator | Container | Iterator used to iterate through a set. |
const_iterator | Container | Const iterator used to iterate through a set. (Iterator and const_iterator are the same type.) |
reverse_iterator | Reversible Container | Iterator used to iterate backwards through a set. |
const_reverse_iterator | Reversible Container | Const iterator used to iterate backwards through a set. (Reverse_iterator and const_reverse_iterator are the same type.) |
iterator begin() const | Container | Returns an iterator pointing to the beginning of the set. |
iterator end() const | Container | Returns an iterator pointing to the end of the set. |
reverse_iterator rbegin() const | Reversible Container | Returns a reverse_iterator pointing to the beginning of the reversed set. |
reverse_iterator rend() const | Reversible Container | Returns a reverse_iterator pointing to the end of the reversed set. |
size_type size() const | Container | Returns the size of the set. |
size_type max_size() const | Container | Returns the largest possible size of the set. |
bool empty() const | Container | true if the set's size is 0. |
key_compare key_comp() const | Sorted Associative Container | Returns the key_compare object used by the set. |
value_compare value_comp() const | Sorted Associative Container | Returns the value_compare object used by the set. |
set() | Container | Creates an empty set. |
set(const key_compare& comp) | Sorted Associative Container | Creates an empty set, using comp as the key_compare object. |
template <class InputIterator> set(InputIterator f, InputIterator l) [1] |
Unique Sorted Associative Container | Creates a set with a copy of a range. |
template <class InputIterator> set(InputIterator f, InputIterator l, const key_compare& comp) [1] |
Unique Sorted Associative Container | Creates a set with a copy of a range, using comp as the key_compare object. |
set(const set&) | Container | The copy constructor. |
set& operator=(const set&) | Container | The assignment operator |
void swap(set&) | Container | Swaps the contents of two sets. |
pair<iterator, bool> insert(const value_type& x) |
Unique Associative Container | Inserts x into the set. |
iterator insert(iterator pos, const value_type& x) |
Unique Sorted Associative Container | Inserts x into the set, using pos as a hint to where it will be inserted. |
template <class InputIterator> void insert(InputIterator, InputIterator) [1] |
Unique Sorted Associative Container | Inserts a range into the set. |
void erase(iterator pos) | Associative Container | Erases the element pointed to by pos. |
size_type erase(const key_type& k) | Associative Container | Erases the element whose key is k. |
void erase(iterator first, iterator last) | Associative Container | Erases all elements in a range. |
iterator find(const key_type& k) const | Associative Container | Finds an element whose key is k. |
size_type count(const key_type& k) const | Unique Associative Container | Counts the number of elements whose key is k. |
iterator lower_bound(const key_type& k) const | Sorted Associative Container | Finds the first element whose key is not less than k. |
iterator upper_bound(const key_type& k) const | Sorted Associative Container | Finds the first element whose key greater than k. |
pair<iterator, iterator> equal_range(const key_type& k) const |
Sorted Associative Container | Finds a range containing all elements whose key is k. |
bool operator==(const set&, const set&) |
Forward Container | Tests two sets for equality. This is a global function, not a member function. |
bool operator<(const set&, const set&) |
Forward Container | Lexicographical comparison. This is a global function, not a member function. |
[1] This member function relies on member template functions, which at present (early 1998) are not supported by all compilers. If your compiler supports member templates, you can call this function with any type of input iterator. If your compiler does not yet support member templates, though, then the arguments must either be of type const value_type* or of type set::const_iterator.