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C++ multiset constructorThere are following five uses of multiset constructor:
SyntaxDefault constructor explicit multiset (const key_compare& comp = key_compare(), const allocator_type& alloc = allocator_type()); //until C++ 11 explicit multiset (const key_compare& comp = key_compare(), const allocator_type& alloc = allocator_type()); explicit multiset (const allocator_type& alloc); //until C++ 14 mutiset(); explicit multiset (const key_compare& comp, const allocator_type& alloc = allocator_type()); //since C++ 14 explicit multiset (const allocator_type& alloc); range constructor template <class InputIterator> multiset (InputIterator first, InputIterator last, const key_compare& comp = key_compare(), const allocator_type& alloc = allocator_type()); //until C++ 11 template <class InputIterator> multiset (InputIterator first, InputIterator last, const key_compare& comp = key_compare(), const allocator_type& = allocator_type()); //until C++ 14 template <class InputIterator> multiset (InputIterator first, InputIterator last, const key_compare& comp = key_compare(), const allocator_type& = allocator_type()); template <class InputIterator> multiset (InputIterator first, InputIterator last, const allocator_type& = allocator_type()); //since C++ 14 copy constructor multiset (const multiset& x); //until C++ 11 multiset (const multiset& x); multiset (const multiset& x, const allocator_type& alloc); //since C++ 11 move constructor multiset (multiset&& x); multiset (multiset&& x, const allocator_type& alloc); //since C++ 11 initializer list constructor multiset (initializer_list<value_type> il, const key_compare& comp = key_compare(), const allocator_type& alloc = allocator_type()); //until C++ 14 multiset (initializer_list<value_type> il, const key_compare& comp = key_compare(), const allocator_type& alloc = allocator_type()); multiset (initializer_list<value_type> il, const allocator_type& alloc = allocator_type()); //since C++ 14 Parametercomp: A comparison function object which takes two key arguments and returns true if first argument goes before the second argument otherwise, it returns false. By default, it uses less<key_type> predicate. alloc: An allocator object use for all memory allocations of this container. first: Input iterator to the first position in a range. last: Input iterator to the last position in a range. x: Another multiset object of the same type. il: An initializer list object from which the elements are to be copied. Return valueConstructor never returns any value. ComplexityFor empty constructors and move constructors, complexity will be constant. For all other cases, complexity will be linear in the distance between the iterators if the elements are already sorted. Iterator validityInvalidate all pointers, iterators, and references related to x if the elements of multiset container are moved in the move constructor. Data RacesAll copied elements are accessed. Exception SafetyNo effects in case an exception is thrown. Example 1Let's see the simple example for default constructor: #include <iostream> #include <set> using namespace std; int main(void) { // Default constructor multiset<char> s; int size = s.size(); cout << "Size of multiset s = " << size; return 0; } Output: Size of multiset = 0 In the above example, s is an empty multiset therefore, size is 0. Example 2Let's see a simple example for range constructor: #include <iostream> #include <set> using namespace std; int main(void) { int evens[] = {2,6,6,8,10}; // Range Constructor multiset<int> mymultiset (evens, evens+5); cout << "Size of multiset container mymultiset is : " << mymultiset.size(); return 0; } Output: Size of multiset container mymultiset is: 5 In the above example, multiset mymultiset is constructed with the elements of evens. Example 3Let's see a simple example for copy constructor: #include <iostream> #include <set> using namespace std; int main(void) { //Default Constructor multiset<int> s1; s1.insert(5); s1.insert(5); cout << "Size of multiset container s1 is : " << s1.size(); // Copy constructor multiset<int> s2(s1); cout << "\nSize of new multiset container s2 is : " << s2.size(); return 0; } Output: Size of multiset container s1 is: 2 Size of new multiset container s2 is: 2 In the above example, s2 is a copy of s1 multiset. Example 4Let's see a simple example for move constructor: #include <iostream> #include <set> using namespace std; int main(void) { // Default constructor multiset<char> s1; s1.insert('x'); s1.insert('y'); s1.insert('y'); cout << "Size of multiset container s1 is : " << s1.size(); // Move constructor multiset<char> s2(move(s1)); cout << "\nSize of new multiset container s2 is : " << s2.size(); return 0; } Output: Size of multiset container s1 is: 3 Size of new multiset container s2 is: 3 In the above example, contents of s1 are moved to s2 multiset. Example 5Let's see a simple example for initializer list constructor: #include <iostream> #include <set> #include <string> using namespace std; int main() { // Initializer list constructor multiset<string> fruit {"orange", "apple", "mango", "apple", "grape"}; cout << "Size of multiset container fruit is: " << fruit.size(); return 0; } Output: Size of multiset container fruit is: 5 The above example creates a multiset fruit with string as key and initializes it with initializer_list.
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