public member function
<map>
key_compare key_comp() const;
Return key comparison object
Returns a copy of the comparison object used by the container to compare keys.
By default, this is a less object, which returns the same as operator<.
This object determines the order of the elements in the container: it is a function pointer or a function object that takes two arguments of the same type as the element keys, and returns true if the first argument is considered to go before the second in the strict weak ordering it defines, and false otherwise.
Two keys are considered equivalent if key_comp returns false reflexively (i.e., no matter the order in which the keys are passed as arguments).
Return value
The comparison object.
Member type key_compare is the type of the comparison object associated to the container, defined in multimap as an alias of its third template parameter (Compare).
Example
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// multimap::key_comp
#include <iostream>
#include <map>
int main ()
{
std::multimap<char,int> mymultimap;
std::multimap<char,int>::key_compare mycomp = mymultimap.key_comp();
mymultimap.insert (std::make_pair('a',100));
mymultimap.insert (std::make_pair('b',200));
mymultimap.insert (std::make_pair('b',211));
mymultimap.insert (std::make_pair('c',300));
std::cout << "mymultimap contains:\n";
char highest = mymultimap.rbegin()->first; // key value of last element
std::multimap<char,int>::iterator it = mymultimap.begin();
do {
std::cout << (*it).first << " => " << (*it).second << '\n';
} while ( mycomp((*it++).first, highest) );
std::cout << '\n';
return 0;
}
| |
Output:
mymultimap contains:
a => 100
b => 200
b => 211
c => 300
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Iterator validity
No changes.
Data races
The container is accessed.
No contained elements are accessed: concurrently accessing or modifying them is safe.
Exception safety
Strong guarantee: if an exception is thrown, there are no changes in the container.