c++ multimap, return submap where key is between MIN and MAX

Question

Using c++, i have a multimap. From this multimap i want to get a submap where the keys are withing a MIN and MAX value.

Somthing like :

mmap->insert(1,classInstance); 
mmap->insert(2,classInstance);
mmap->insert(3,classInstance);
mmap->insert(4,classInstance);
mmap->insert(2,classInstance2);
mmap->insert(5,classInstance);
mmap->insert(6,classInstance);

submap = mmap->submap(2,5);

result is a submap with 
2,classInstance
3,classInstance
4,classInstance
2,classInstance2
5,classInstance
as values

How would i achieved this ? Thanks !

Answer 1

You can use class member functions lower_bound and upper_bound.

Here is a demonstrative program

#include <iostream>
#include <map>

struct classInstance {};

int main() 
{
    std::multimap<int, classInstance> mmap;

    mmap.insert( { 1, classInstance() } ); 
    mmap.insert( { 2, classInstance() } );
    mmap.insert( { 3, classInstance() } );
    mmap.insert( { 4, classInstance() } );
    mmap.insert( { 2, classInstance() } );
    mmap.insert( { 5, classInstance() } );
    mmap.insert( { 6, classInstance() } );

    auto first = mmap.lower_bound( 2 );
    auto last  = mmap.upper_bound( 5 );

    while ( first != last ) std::cout << first++->first << std::endl;
}

The program output is

2
2
3
4
5

The while loop can be substituted for the for loop like

    for ( ; first != last; ++first ) std::cout << first->first << std::endl;