STL Multiset with Class Objects sorted based on its member variable

[Digital Don]

Hi,

I was looking at the MultiSet STL structure with some "less" keyword. I was told that we can use the "MultiSet" STL structure to automatically sort the content.

Is it possible to store and Sort CLASS objects based on a class variable value in it .

i.e.

multiset <Event, less<Event> > _queue;

where Event is a class with the variables in it

"processID
Time
typeofEvent"

How do I specify that the class objects in the multiset be sorted based on the TIME value of the class object?

Thank You in Advance.

[Laharl]

You can overload operator< for your class. That is, you write a function with the signature

bool operator<(const Event& other)

that returns based on whether the caller object's time value (use the 'this' pointer if you want) is less than the passed in object's time value.

[weaknessforcats]

You can also create your multiset using a 3rd template parameter for the address of the function you want to use to order your objects.

This avoids implementing a class operator< when you don't really need it.

[Digital Don]

Can u explain or provide a link to the 3rd template of Multiset?

Thank You.

You can also create your multiset using a 3rd template parameter for the address of the function you want to use to order your objects.

This avoids implementing a class operator< when you don't really need it.

[Laharl]

The STL declaration of multiset is

multiset<class Key, class Comparator = less<Key>, class Allocator = Allocator<Key> >

Thus, it's the second parameter you're interested in here, not the third. This works because the name of a function acts as a pointer to that function.

class foo{
 private
  int bar;
 //...
}
 
bool myfunc(const foo& one, const foo& two){
 return one.bar<two.bar;
}
 
multiset<foo, myfunc> myset;