C++ std::multiset

std::multiset

template < class T,                        // multiset::key_type/value_type
           class Compare = less<T>,        // multiset::key_compare/value_compare
           class Alloc = allocator<T> >    // multiset::allocator_type
           > class multiset;

Multiple-key set

Multisets are containers that store elements following a specific order, and where multiple elements can have equivalent values.

In a multiset, the value of an element also identifies it (the value is itself the key, of type T). The value of the elements in a multiset cannot be modified once in the container (the elements are always const), but they can be inserted or removed from the container.

Internally, the elements in a multiset are always sorted following a specific strict weak ordering criterion indicated by its internal comparison object (of type Compare).

multiset containers are generally slower than unordered_multiset containers to access individual elements by their key, but they allow the direct iteration on subsets based on their order.

Multisets are typically implemented as binary search trees.

Container properties

• Associative Elements in associative containers are referenced by their key and not by their absolute position in the container.
• Ordered The elements in the container follow a strict order at all times. All inserted elements are given a position in this order.
• Set The value of an element is also the key used to identify it.
• Multiple equivalent keys Multiple elements in the container can have equivalent keys.
• Allocator-aware The container uses an allocator object to dynamically handle its storage needs.

** Other Function please see the std::set container **

Code Example

#include <iostream>
#include <set>
using namespace std;
bool fncomp(int lhs, int rhs)
{ return lhs < rhs; }
struct classcomp
{
    bool operator() (const int& lhs, const int& rhs) const
    { return lhs<rhs; }
};
int main(int argc, char **argv)
{
    multiset<int> first;
    int myints[] = {10,20,30,20,20};
    multiset<int> first1(myints, myints+5);
    multiset<int> first2(first1);
    multiset<int> first3(first2.begin(),first2.end());
    multiset<int, classcomp> first4;
    bool (*fn_pt)(int,int) = fncomp;
    multiset<int, bool(*)(int,int)> first5(fn_pt);
    /** other function please to reference other container */
    return 0;
}

Reference

cplusplus